diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index e3dbb018c..c136ca4b1 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -527,7 +527,7 @@ jobs:
           report_name: Coverage Backend
           type: lcov
           result_path: ./backend/coverage/lcov.info
-          min_coverage: 74
+          min_coverage: 76
           token: ${{ github.token }}
 
   ##########################################################################
diff --git a/backend/.env.dist b/backend/.env.dist
index 861e5ebb3..b238388f6 100644
--- a/backend/.env.dist
+++ b/backend/.env.dist
@@ -1,4 +1,4 @@
-CONFIG_VERSION=v13.2022-12-20
+CONFIG_VERSION=v14.2022-12-22
 
 # Server
 PORT=4000
@@ -67,3 +67,4 @@ EVENT_PROTOCOL_DISABLED=false
 # on an hash created from this topic
 # FEDERATION_DHT_TOPIC=GRADIDO_HUB
 # FEDERATION_DHT_SEED=64ebcb0e3ad547848fef4197c6e2332f 
+# FEDERATION_COMMUNITY_URL=http://localhost:4000/api
diff --git a/backend/.env.template b/backend/.env.template
index 9d8696c6a..f73b87353 100644
--- a/backend/.env.template
+++ b/backend/.env.template
@@ -60,3 +60,4 @@ EVENT_PROTOCOL_DISABLED=$EVENT_PROTOCOL_DISABLED
 # Federation
 FEDERATION_DHT_TOPIC=$FEDERATION_DHT_TOPIC
 FEDERATION_DHT_SEED=$FEDERATION_DHT_SEED
+FEDERATION_COMMUNITY_URL=$FEDERATION_COMMUNITY_URL
diff --git a/backend/package.json b/backend/package.json
index 4e34ca566..69a436563 100644
--- a/backend/package.json
+++ b/backend/package.json
@@ -20,6 +20,7 @@
   "dependencies": {
     "@hyperswarm/dht": "^6.2.0",
     "apollo-server-express": "^2.25.2",
+    "await-semaphore": "^0.1.3",
     "axios": "^0.21.1",
     "class-validator": "^0.13.1",
     "cors": "^2.8.5",
diff --git a/backend/src/config/index.ts b/backend/src/config/index.ts
index 4d605857f..698b17e67 100644
--- a/backend/src/config/index.ts
+++ b/backend/src/config/index.ts
@@ -10,14 +10,14 @@ Decimal.set({
 })
 
 const constants = {
-  DB_VERSION: '0057-clear_old_password_junk',
+  DB_VERSION: '0058-add_communities_table',
   DECAY_START_TIME: new Date('2021-05-13 17:46:31-0000'), // GMT+0
   LOG4JS_CONFIG: 'log4js-config.json',
   // default log level on production should be info
   LOG_LEVEL: process.env.LOG_LEVEL || 'info',
   CONFIG_VERSION: {
     DEFAULT: 'DEFAULT',
-    EXPECTED: 'v13.2022-12-20',
+    EXPECTED: 'v14.2022-11-22',
     CURRENT: '',
   },
 }
@@ -120,6 +120,12 @@ if (
 const federation = {
   FEDERATION_DHT_TOPIC: process.env.FEDERATION_DHT_TOPIC || null,
   FEDERATION_DHT_SEED: process.env.FEDERATION_DHT_SEED || null,
+  FEDERATION_COMMUNITY_URL:
+    process.env.FEDERATION_COMMUNITY_URL === undefined
+      ? null
+      : process.env.FEDERATION_COMMUNITY_URL.endsWith('/')
+      ? process.env.FEDERATION_COMMUNITY_URL
+      : process.env.FEDERATION_COMMUNITY_URL + '/',
 }
 
 const CONFIG = {
diff --git a/backend/src/federation/index.test.ts b/backend/src/federation/index.test.ts
new file mode 100644
index 000000000..235206cf8
--- /dev/null
+++ b/backend/src/federation/index.test.ts
@@ -0,0 +1,798 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+
+import { startDHT } from './index'
+import DHT from '@hyperswarm/dht'
+import CONFIG from '@/config'
+import { logger } from '@test/testSetup'
+import { Community as DbCommunity } from '@entity/Community'
+import { testEnvironment, cleanDB } from '@test/helpers'
+
+CONFIG.FEDERATION_DHT_SEED = '64ebcb0e3ad547848fef4197c6e2332f'
+
+jest.mock('@hyperswarm/dht')
+
+const TEST_TOPIC = 'gradido_test_topic'
+
+const keyPairMock = {
+  publicKey: Buffer.from('publicKey'),
+  secretKey: Buffer.from('secretKey'),
+}
+
+const serverListenSpy = jest.fn()
+
+const serverEventMocks: { [key: string]: any } = {}
+
+const serverOnMock = jest.fn().mockImplementation((key: string, callback) => {
+  serverEventMocks[key] = callback
+})
+
+const nodeCreateServerMock = jest.fn().mockImplementation(() => {
+  return {
+    on: serverOnMock,
+    listen: serverListenSpy,
+  }
+})
+
+const nodeAnnounceMock = jest.fn().mockImplementation(() => {
+  return {
+    finished: jest.fn(),
+  }
+})
+
+const lookupResultMock = {
+  token: Buffer.from(TEST_TOPIC),
+  from: {
+    id: Buffer.from('somone'),
+    host: '188.95.53.5',
+    port: 63561,
+  },
+  to: { id: null, host: '83.53.31.27', port: 55723 },
+  peers: [
+    {
+      publicKey: Buffer.from('some-public-key'),
+      relayAddresses: [],
+    },
+  ],
+}
+
+const nodeLookupMock = jest.fn().mockResolvedValue([lookupResultMock])
+
+const socketEventMocks: { [key: string]: any } = {}
+
+const socketOnMock = jest.fn().mockImplementation((key: string, callback) => {
+  socketEventMocks[key] = callback
+})
+
+const socketWriteMock = jest.fn()
+
+const nodeConnectMock = jest.fn().mockImplementation(() => {
+  return {
+    on: socketOnMock,
+    once: socketOnMock,
+    write: socketWriteMock,
+  }
+})
+
+DHT.hash.mockImplementation(() => {
+  return Buffer.from(TEST_TOPIC)
+})
+
+DHT.keyPair.mockImplementation(() => {
+  return keyPairMock
+})
+
+DHT.mockImplementation(() => {
+  return {
+    createServer: nodeCreateServerMock,
+    announce: nodeAnnounceMock,
+    lookup: nodeLookupMock,
+    connect: nodeConnectMock,
+  }
+})
+
+let con: any
+let testEnv: any
+
+beforeAll(async () => {
+  testEnv = await testEnvironment(logger)
+  con = testEnv.con
+  await cleanDB()
+})
+
+afterAll(async () => {
+  await cleanDB()
+  await con.close()
+})
+
+describe('federation', () => {
+  beforeAll(() => {
+    jest.useFakeTimers()
+  })
+
+  describe('call startDHT', () => {
+    const hashSpy = jest.spyOn(DHT, 'hash')
+    const keyPairSpy = jest.spyOn(DHT, 'keyPair')
+    beforeEach(async () => {
+      DHT.mockClear()
+      jest.clearAllMocks()
+      await startDHT(TEST_TOPIC)
+    })
+
+    it('calls DHT.hash', () => {
+      expect(hashSpy).toBeCalledWith(Buffer.from(TEST_TOPIC))
+    })
+
+    it('creates a key pair', () => {
+      expect(keyPairSpy).toBeCalledWith(expect.any(Buffer))
+    })
+
+    it('initializes a new DHT object', () => {
+      expect(DHT).toBeCalledWith({ keyPair: keyPairMock })
+    })
+
+    describe('DHT node', () => {
+      it('creates a server', () => {
+        expect(nodeCreateServerMock).toBeCalled()
+      })
+
+      it('listens on the server', () => {
+        expect(serverListenSpy).toBeCalled()
+      })
+
+      describe('timers', () => {
+        beforeEach(() => {
+          jest.runOnlyPendingTimers()
+        })
+
+        it('announces on topic', () => {
+          expect(nodeAnnounceMock).toBeCalledWith(Buffer.from(TEST_TOPIC), keyPairMock)
+        })
+
+        it('looks up on topic', () => {
+          expect(nodeLookupMock).toBeCalledWith(Buffer.from(TEST_TOPIC))
+        })
+      })
+
+      describe('server connection event', () => {
+        beforeEach(() => {
+          serverEventMocks.connection({
+            remotePublicKey: Buffer.from('another-public-key'),
+            on: socketOnMock,
+          })
+        })
+
+        it('can be triggered', () => {
+          expect(socketOnMock).toBeCalled()
+        })
+
+        describe('socket events', () => {
+          describe('on data', () => {
+            describe('with receiving simply a string', () => {
+              beforeEach(() => {
+                jest.clearAllMocks()
+                socketEventMocks.data(Buffer.from('no-json string'))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith('data: no-json string')
+              })
+
+              it('logs an error of unexpected data format and structure', () => {
+                expect(logger.error).toBeCalledWith(
+                  'Error on receiving data from socket:',
+                  new SyntaxError('Unexpected token o in JSON at position 1'),
+                )
+              })
+            })
+
+            describe('with receiving array of strings', () => {
+              beforeEach(() => {
+                jest.clearAllMocks()
+                const strArray: string[] = ['invalid type test', 'api', 'url']
+                socketEventMocks.data(Buffer.from(strArray.toString()))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith('data: invalid type test,api,url')
+              })
+
+              it('logs an error of unexpected data format and structure', () => {
+                expect(logger.error).toBeCalledWith(
+                  'Error on receiving data from socket:',
+                  new SyntaxError('Unexpected token i in JSON at position 0'),
+                )
+              })
+            })
+
+            describe('with receiving array of string-arrays', () => {
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                const strArray: string[][] = [
+                  [`api`, `url`, `invalid type in array test`],
+                  [`wrong`, `api`, `url`],
+                ]
+                await socketEventMocks.data(Buffer.from(strArray.toString()))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(
+                  'data: api,url,invalid type in array test,wrong,api,url',
+                )
+              })
+
+              it('logs an error of unexpected data format and structure', () => {
+                expect(logger.error).toBeCalledWith(
+                  'Error on receiving data from socket:',
+                  new SyntaxError('Unexpected token a in JSON at position 0'),
+                )
+              })
+            })
+
+            describe('with receiving JSON-Array with too much entries', () => {
+              let jsonArray: { api: string; url: string }[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 'v1_0', url: 'too much versions at the same time test' },
+                  { api: 'v1_0', url: 'url2' },
+                  { api: 'v1_0', url: 'url3' },
+                  { api: 'v1_0', url: 'url4' },
+                  { api: 'v1_0', url: 'url5' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(
+                  'data: [{"api":"v1_0","url":"too much versions at the same time test"},{"api":"v1_0","url":"url2"},{"api":"v1_0","url":"url3"},{"api":"v1_0","url":"url4"},{"api":"v1_0","url":"url5"}]',
+                )
+              })
+
+              it('logs a warning of too much apiVersion-Definitions', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received totaly wrong or too much apiVersions-Definition JSON-String: ${JSON.stringify(
+                    jsonArray,
+                  )}`,
+                )
+              })
+            })
+
+            describe('with receiving wrong but tolerated property data', () => {
+              let jsonArray: any[]
+              let result: DbCommunity[] = []
+              beforeAll(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    wrong: 'wrong but tolerated property test',
+                    api: 'v1_0',
+                    url: 'url1',
+                  },
+                  {
+                    api: 'v2_0',
+                    url: 'url2',
+                    wrong: 'wrong but tolerated property test',
+                  },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+                result = await DbCommunity.find()
+              })
+
+              afterAll(async () => {
+                await cleanDB()
+              })
+
+              it('has two Communty entries in database', () => {
+                expect(result).toHaveLength(2)
+              })
+
+              it('has an entry for api version v1_0', () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'v1_0',
+                      endPoint: 'url1',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+
+              it('has an entry for api version v2_0', () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'v2_0',
+                      endPoint: 'url2',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+            })
+
+            describe('with receiving data but missing api property', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { test1: 'missing api proterty test', url: 'any url definition as string' },
+                  { api: 'some api', test2: 'missing url property test' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(jsonArray[0])}`,
+                )
+              })
+            })
+
+            describe('with receiving data but missing url property', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 'some api', test2: 'missing url property test' },
+                  { test1: 'missing api proterty test', url: 'any url definition as string' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(jsonArray[0])}`,
+                )
+              })
+            })
+
+            describe('with receiving data but wrong type of api property', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 1, url: 'wrong property type tests' },
+                  { api: 'urltyptest', url: 2 },
+                  { api: 1, url: 2 },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(jsonArray[0])}`,
+                )
+              })
+            })
+
+            describe('with receiving data but wrong type of url property', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 'urltyptest', url: 2 },
+                  { api: 1, url: 'wrong property type tests' },
+                  { api: 1, url: 2 },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(jsonArray[0])}`,
+                )
+              })
+            })
+
+            describe('with receiving data but wrong type of both properties', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 1, url: 2 },
+                  { api: 'urltyptest', url: 2 },
+                  { api: 1, url: 'wrong property type tests' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(jsonArray[0])}`,
+                )
+              })
+            })
+
+            describe('with receiving data but too long api string', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  { api: 'toolong api', url: 'some valid url' },
+                  {
+                    api: 'valid  api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                  {
+                    api: 'toolong api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received apiVersion with content longer than max length: ${JSON.stringify(
+                    jsonArray[0],
+                  )}`,
+                )
+              })
+            })
+
+            describe('with receiving data but too long url string', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    api: 'api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                  { api: 'toolong api', url: 'some valid url' },
+                  {
+                    api: 'toolong api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+
+              it('logs a warning of invalid apiVersion-Definition', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received apiVersion with content longer than max length: ${JSON.stringify(
+                    jsonArray[0],
+                  )}`,
+                )
+              })
+            })
+
+            describe('with receiving data but both properties with too long strings', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    api: 'toolong api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                  {
+                    api: 'api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                  { api: 'toolong api', url: 'some valid url' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.info).toBeCalledWith(`data: ${JSON.stringify(jsonArray)}`)
+              })
+            })
+
+            describe('with receiving data of exact max allowed properties length', () => {
+              let jsonArray: any[]
+              let result: DbCommunity[] = []
+              beforeAll(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    api: 'valid  api',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'api',
+                    url: 'this is a too long url definition with exact one character more than the allowed two hundert and fiftyfive characters. and here begins the fill characters with no sense of content menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmic',
+                  },
+                  { api: 'toolong api', url: 'some valid url' },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+                result = await DbCommunity.find()
+              })
+
+              afterAll(async () => {
+                await cleanDB()
+              })
+
+              it('has one Communty entry in database', () => {
+                expect(result).toHaveLength(1)
+              })
+
+              it(`has an entry with max content length for api and url`, () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'valid  api',
+                      endPoint:
+                        'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+            })
+
+            describe('with receiving data of exact max allowed buffer length', () => {
+              let jsonArray: any[]
+              let result: DbCommunity[] = []
+              beforeAll(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    api: 'valid api1',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api2',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api3',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api4',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+                result = await DbCommunity.find()
+              })
+
+              afterAll(async () => {
+                await cleanDB()
+              })
+
+              it('has five Communty entries in database', () => {
+                expect(result).toHaveLength(4)
+              })
+
+              it(`has an entry 'valid api1' with max content length for api and url`, () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'valid api1',
+                      endPoint:
+                        'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+
+              it(`has an entry 'valid api2' with max content length for api and url`, () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'valid api2',
+                      endPoint:
+                        'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+
+              it(`has an entry 'valid api3' with max content length for api and url`, () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'valid api3',
+                      endPoint:
+                        'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+
+              it(`has an entry 'valid api4' with max content length for api and url`, () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'valid api4',
+                      endPoint:
+                        'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+            })
+
+            describe('with receiving data longer than max allowed buffer length', () => {
+              let jsonArray: any[]
+              beforeEach(async () => {
+                jest.clearAllMocks()
+                jsonArray = [
+                  {
+                    api: 'Xvalid api1',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api2',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api3',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                  {
+                    api: 'valid api4',
+                    url: 'this is a valid url definition with exact the max allowed length of two hundert and fiftyfive characters. and here begins the fill characters with no sense of content kuhwarmiga menschhabicheinhungerdassichnichtweiswoichheutnachtschlafensollsofriertesmich',
+                  },
+                ]
+                await socketEventMocks.data(Buffer.from(JSON.stringify(jsonArray)))
+              })
+
+              it('logs the received data', () => {
+                expect(logger.warn).toBeCalledWith(
+                  `received more than max allowed length of data buffer: ${
+                    JSON.stringify(jsonArray).length
+                  } against 1141 max allowed`,
+                )
+              })
+            })
+
+            describe('with proper data', () => {
+              let result: DbCommunity[] = []
+              beforeAll(async () => {
+                jest.clearAllMocks()
+                await socketEventMocks.data(
+                  Buffer.from(
+                    JSON.stringify([
+                      {
+                        api: 'v1_0',
+                        url: 'http://localhost:4000/api/v1_0',
+                      },
+                      {
+                        api: 'v2_0',
+                        url: 'http://localhost:4000/api/v2_0',
+                      },
+                    ]),
+                  ),
+                )
+                result = await DbCommunity.find()
+              })
+
+              afterAll(async () => {
+                await cleanDB()
+              })
+
+              it('has two Communty entries in database', () => {
+                expect(result).toHaveLength(2)
+              })
+
+              it('has an entry for api version v1_0', () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'v1_0',
+                      endPoint: 'http://localhost:4000/api/v1_0',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+
+              it('has an entry for api version v2_0', () => {
+                expect(result).toEqual(
+                  expect.arrayContaining([
+                    expect.objectContaining({
+                      id: expect.any(Number),
+                      publicKey: expect.any(Buffer),
+                      apiVersion: 'v2_0',
+                      endPoint: 'http://localhost:4000/api/v2_0',
+                      lastAnnouncedAt: expect.any(Date),
+                      createdAt: expect.any(Date),
+                      updatedAt: null,
+                    }),
+                  ]),
+                )
+              })
+            })
+          })
+
+          describe('on open', () => {
+            beforeEach(() => {
+              socketEventMocks.open()
+            })
+
+            it.skip('calls socket write with own api versions', () => {
+              expect(socketWriteMock).toBeCalledWith(
+                Buffer.from(
+                  JSON.stringify([
+                    {
+                      api: 'v1_0',
+                      url: 'http://localhost:4000/api/v1_0',
+                    },
+                    {
+                      api: 'v1_1',
+                      url: 'http://localhost:4000/api/v1_1',
+                    },
+                    {
+                      api: 'v2_0',
+                      url: 'http://localhost:4000/api/v2_0',
+                    },
+                  ]),
+                ),
+              )
+            })
+          })
+        })
+      })
+    })
+  })
+})
diff --git a/backend/src/federation/index.ts b/backend/src/federation/index.ts
index 82b961c63..ebaaed5e2 100644
--- a/backend/src/federation/index.ts
+++ b/backend/src/federation/index.ts
@@ -1,14 +1,9 @@
 /* eslint-disable @typescript-eslint/no-explicit-any */
 /* eslint-disable @typescript-eslint/explicit-module-boundary-types */
-
 import DHT from '@hyperswarm/dht'
-// import { Connection } from '@dbTools/typeorm'
 import { backendLogger as logger } from '@/server/logger'
 import CONFIG from '@/config'
-
-function between(min: number, max: number) {
-  return Math.floor(Math.random() * (max - min + 1) + min)
-}
+import { Community as DbCommunity } from '@entity/Community'
 
 const KEY_SECRET_SEEDBYTES = 32
 const getSeed = (): Buffer | null =>
@@ -18,37 +13,107 @@ const POLLTIME = 20000
 const SUCCESSTIME = 120000
 const ERRORTIME = 240000
 const ANNOUNCETIME = 30000
-const nodeRand = between(1, 99)
-const nodeURL = `https://test${nodeRand}.org`
-const nodeAPI = {
-  API_1_00: `${nodeURL}/api/1_00/`,
-  API_1_01: `${nodeURL}/api/1_01/`,
-  API_2_00: `${nodeURL}/graphql/2_00/`,
+
+enum ApiVersionType {
+  V1_0 = 'v1_0',
+  V1_1 = 'v1_1',
+  V2_0 = 'v2_0',
+}
+type CommunityApi = {
+  api: string
+  url: string
 }
 
-export const startDHT = async (
-  // connection: Connection,
-  topic: string,
-): Promise<void> => {
+export const startDHT = async (topic: string): Promise<void> => {
   try {
     const TOPIC = DHT.hash(Buffer.from(topic))
     const keyPair = DHT.keyPair(getSeed())
     logger.info(`keyPairDHT: publicKey=${keyPair.publicKey.toString('hex')}`)
     logger.debug(`keyPairDHT: secretKey=${keyPair.secretKey.toString('hex')}`)
 
+    const ownApiVersions = Object.values(ApiVersionType).map(function (apiEnum) {
+      const comApi: CommunityApi = {
+        api: apiEnum,
+        url: CONFIG.FEDERATION_COMMUNITY_URL + apiEnum,
+      }
+      return comApi
+    })
+    logger.debug(`ApiList: ${JSON.stringify(ownApiVersions)}`)
+
     const node = new DHT({ keyPair })
 
     const server = node.createServer()
 
     server.on('connection', function (socket: any) {
-      // noiseSocket is E2E between you and the other peer
-      // pipe it somewhere like any duplex stream
-      logger.info(`Remote public key: ${socket.remotePublicKey.toString('hex')}`)
-      // console.log("Local public key", noiseSocket.publicKey.toString("hex")); // same as keyPair.publicKey
+      logger.info(`server on... with Remote public key: ${socket.remotePublicKey.toString('hex')}`)
 
-      socket.on('data', (data: Buffer) => logger.info(`data: ${data.toString('ascii')}`))
+      socket.on('data', async (data: Buffer) => {
+        try {
+          if (data.length > 1141) {
+            logger.warn(
+              `received more than max allowed length of data buffer: ${data.length} against 1141 max allowed`,
+            )
+            return
+          }
+          logger.info(`data: ${data.toString('ascii')}`)
+          const recApiVersions: CommunityApi[] = JSON.parse(data.toString('ascii'))
 
-      // process.stdin.pipe(noiseSocket).pipe(process.stdout);
+          // TODO better to introduce the validation by https://github.com/typestack/class-validato
+          if (recApiVersions && Array.isArray(recApiVersions) && recApiVersions.length < 5) {
+            for (const recApiVersion of recApiVersions) {
+              if (
+                !recApiVersion.api ||
+                typeof recApiVersion.api !== 'string' ||
+                !recApiVersion.url ||
+                typeof recApiVersion.url !== 'string'
+              ) {
+                logger.warn(
+                  `received invalid apiVersion-Definition: ${JSON.stringify(recApiVersion)}`,
+                )
+                // in a forEach-loop use return instead of continue
+                return
+              }
+              // TODO better to introduce the validation on entity-Level by https://github.com/typestack/class-validator
+              if (recApiVersion.api.length > 10 || recApiVersion.url.length > 255) {
+                logger.warn(
+                  `received apiVersion with content longer than max length: ${JSON.stringify(
+                    recApiVersion,
+                  )}`,
+                )
+                // in a forEach-loop use return instead of continue
+                return
+              }
+
+              const variables = {
+                apiVersion: recApiVersion.api,
+                endPoint: recApiVersion.url,
+                publicKey: socket.remotePublicKey.toString('hex'),
+                lastAnnouncedAt: new Date(),
+              }
+              logger.debug(`upsert with variables=${JSON.stringify(variables)}`)
+              // this will NOT update the updatedAt column, to distingue between a normal update and the last announcement
+              await DbCommunity.createQueryBuilder()
+                .insert()
+                .into(DbCommunity)
+                .values(variables)
+                .orUpdate({
+                  conflict_target: ['id', 'publicKey', 'apiVersion'],
+                  overwrite: ['end_point', 'last_announced_at'],
+                })
+                .execute()
+              logger.info(`federation community upserted successfully...`)
+            }
+          } else {
+            logger.warn(
+              `received totaly wrong or too much apiVersions-Definition JSON-String: ${JSON.stringify(
+                recApiVersions,
+              )}`,
+            )
+          }
+        } catch (e) {
+          logger.error('Error on receiving data from socket:', e)
+        }
+      })
     })
 
     await server.listen()
@@ -93,7 +158,6 @@ export const startDHT = async (
       logger.info(`Found new peers: ${collectedPubKeys}`)
 
       collectedPubKeys.forEach((remotePubKey) => {
-        // publicKey here is keyPair.publicKey from above
         const socket = node.connect(Buffer.from(remotePubKey, 'hex'))
 
         // socket.once("connect", function () {
@@ -110,17 +174,12 @@ export const startDHT = async (
         })
 
         socket.on('open', function () {
-          // noiseSocket fully open with the other peer
-          // console.log("writing to socket");
-          socket.write(Buffer.from(`${nodeRand}`))
-          socket.write(Buffer.from(JSON.stringify(nodeAPI)))
+          socket.write(Buffer.from(JSON.stringify(ownApiVersions)))
           successfulRequests.push(remotePubKey)
         })
-        // pipe it somewhere like any duplex stream
-        // process.stdin.pipe(noiseSocket).pipe(process.stdout)
       })
     }, POLLTIME)
   } catch (err) {
-    logger.error(err)
+    logger.error('DHT unexpected error:', err)
   }
 }
diff --git a/backend/src/graphql/resolver/ContributionResolver.test.ts b/backend/src/graphql/resolver/ContributionResolver.test.ts
index 387018624..cf2d55d94 100644
--- a/backend/src/graphql/resolver/ContributionResolver.test.ts
+++ b/backend/src/graphql/resolver/ContributionResolver.test.ts
@@ -1961,8 +1961,7 @@ describe('ContributionResolver', () => {
               })
             })
 
-            // In the futrue this should not throw anymore
-            it('throws an error for the second confirmation', async () => {
+            it('throws no error for the second confirmation', async () => {
               const r1 = mutate({
                 mutation: confirmContribution,
                 variables: {
@@ -1982,8 +1981,7 @@ describe('ContributionResolver', () => {
               )
               await expect(r2).resolves.toEqual(
                 expect.objectContaining({
-                  // data: { confirmContribution: true },
-                  errors: [new GraphQLError('Creation was not successful.')],
+                  data: { confirmContribution: true },
                 }),
               )
             })
diff --git a/backend/src/graphql/resolver/ContributionResolver.ts b/backend/src/graphql/resolver/ContributionResolver.ts
index 32c72b9b1..2587aab61 100644
--- a/backend/src/graphql/resolver/ContributionResolver.ts
+++ b/backend/src/graphql/resolver/ContributionResolver.ts
@@ -50,6 +50,7 @@ import {
   sendContributionConfirmedEmail,
   sendContributionRejectedEmail,
 } from '@/emails/sendEmailVariants'
+import { TRANSACTIONS_LOCK } from '@/util/TRANSACTIONS_LOCK'
 
 @Resolver()
 export class ContributionResolver {
@@ -579,8 +580,10 @@ export class ContributionResolver {
       clientTimezoneOffset,
     )
 
-    const receivedCallDate = new Date()
+    // acquire lock
+    const releaseLock = await TRANSACTIONS_LOCK.acquire()
 
+    const receivedCallDate = new Date()
     const queryRunner = getConnection().createQueryRunner()
     await queryRunner.connect()
     await queryRunner.startTransaction('REPEATABLE READ') // 'READ COMMITTED')
@@ -590,7 +593,7 @@ export class ContributionResolver {
         .select('transaction')
         .from(DbTransaction, 'transaction')
         .where('transaction.userId = :id', { id: contribution.userId })
-        .orderBy('transaction.balanceDate', 'DESC')
+        .orderBy('transaction.id', 'DESC')
         .getOne()
       logger.info('lastTransaction ID', lastTransaction ? lastTransaction.id : 'undefined')
 
@@ -639,10 +642,11 @@ export class ContributionResolver {
       })
     } catch (e) {
       await queryRunner.rollbackTransaction()
-      logger.error(`Creation was not successful: ${e}`)
-      throw new Error(`Creation was not successful.`)
+      logger.error('Creation was not successful', e)
+      throw new Error('Creation was not successful.')
     } finally {
       await queryRunner.release()
+      releaseLock()
     }
 
     const event = new Event()
diff --git a/backend/src/graphql/resolver/TransactionLinkResolver.test.ts b/backend/src/graphql/resolver/TransactionLinkResolver.test.ts
index 28422af26..9f7d30244 100644
--- a/backend/src/graphql/resolver/TransactionLinkResolver.test.ts
+++ b/backend/src/graphql/resolver/TransactionLinkResolver.test.ts
@@ -23,6 +23,11 @@ import { User } from '@entity/User'
 import { UnconfirmedContribution } from '@model/UnconfirmedContribution'
 import Decimal from 'decimal.js-light'
 import { GraphQLError } from 'graphql'
+import { TRANSACTIONS_LOCK } from '@/util/TRANSACTIONS_LOCK'
+
+// mock semaphore to allow use fake timers
+jest.mock('@/util/TRANSACTIONS_LOCK')
+TRANSACTIONS_LOCK.acquire = jest.fn().mockResolvedValue(jest.fn())
 
 let mutate: any, query: any, con: any
 let testEnv: any
@@ -185,8 +190,7 @@ describe('TransactionLinkResolver', () => {
       describe('after one day', () => {
         beforeAll(async () => {
           jest.useFakeTimers()
-          /* eslint-disable-next-line @typescript-eslint/no-empty-function */
-          setTimeout(() => {}, 1000 * 60 * 60 * 24)
+          setTimeout(jest.fn(), 1000 * 60 * 60 * 24)
           jest.runAllTimers()
           await mutate({
             mutation: login,
diff --git a/backend/src/graphql/resolver/TransactionLinkResolver.ts b/backend/src/graphql/resolver/TransactionLinkResolver.ts
index 9041aae67..897cf9252 100644
--- a/backend/src/graphql/resolver/TransactionLinkResolver.ts
+++ b/backend/src/graphql/resolver/TransactionLinkResolver.ts
@@ -31,6 +31,7 @@ import { calculateDecay } from '@/util/decay'
 import { getUserCreation, validateContribution } from './util/creations'
 import { executeTransaction } from './TransactionResolver'
 import QueryLinkResult from '@union/QueryLinkResult'
+import { TRANSACTIONS_LOCK } from '@/util/TRANSACTIONS_LOCK'
 
 // TODO: do not export, test it inside the resolver
 export const transactionLinkCode = (date: Date): string => {
@@ -165,10 +166,12 @@ export class TransactionLinkResolver {
   ): Promise<boolean> {
     const clientTimezoneOffset = getClientTimezoneOffset(context)
     const user = getUser(context)
-    const now = new Date()
 
     if (code.match(/^CL-/)) {
+      // acquire lock
+      const releaseLock = await TRANSACTIONS_LOCK.acquire()
       logger.info('redeem contribution link...')
+      const now = new Date()
       const queryRunner = getConnection().createQueryRunner()
       await queryRunner.connect()
       await queryRunner.startTransaction('REPEATABLE READ')
@@ -273,7 +276,7 @@ export class TransactionLinkResolver {
           .select('transaction')
           .from(DbTransaction, 'transaction')
           .where('transaction.userId = :id', { id: user.id })
-          .orderBy('transaction.balanceDate', 'DESC')
+          .orderBy('transaction.id', 'DESC')
           .getOne()
         let newBalance = new Decimal(0)
 
@@ -309,9 +312,11 @@ export class TransactionLinkResolver {
         throw new Error(`Creation from contribution link was not successful. ${e}`)
       } finally {
         await queryRunner.release()
+        releaseLock()
       }
       return true
     } else {
+      const now = new Date()
       const transactionLink = await DbTransactionLink.findOneOrFail({ code })
       const linkedUser = await DbUser.findOneOrFail(
         { id: transactionLink.userId },
@@ -322,6 +327,9 @@ export class TransactionLinkResolver {
         throw new Error('Cannot redeem own transaction link.')
       }
 
+      // TODO: The now check should be done within the semaphore lock,
+      // since the program might wait a while till it is ready to proceed
+      // writing the transaction.
       if (transactionLink.validUntil.getTime() < now.getTime()) {
         throw new Error('Transaction Link is not valid anymore.')
       }
diff --git a/backend/src/graphql/resolver/TransactionResolver.test.ts b/backend/src/graphql/resolver/TransactionResolver.test.ts
index 1d4fe5708..6115ef846 100644
--- a/backend/src/graphql/resolver/TransactionResolver.test.ts
+++ b/backend/src/graphql/resolver/TransactionResolver.test.ts
@@ -368,5 +368,74 @@ describe('send coins', () => {
         )
       })
     })
+
+    describe('more transactions to test semaphore', () => {
+      it('sends the coins four times in a row', async () => {
+        await expect(
+          mutate({
+            mutation: sendCoins,
+            variables: {
+              email: 'peter@lustig.de',
+              amount: 10,
+              memo: 'first transaction',
+            },
+          }),
+        ).resolves.toEqual(
+          expect.objectContaining({
+            data: {
+              sendCoins: 'true',
+            },
+          }),
+        )
+        await expect(
+          mutate({
+            mutation: sendCoins,
+            variables: {
+              email: 'peter@lustig.de',
+              amount: 20,
+              memo: 'second transaction',
+            },
+          }),
+        ).resolves.toEqual(
+          expect.objectContaining({
+            data: {
+              sendCoins: 'true',
+            },
+          }),
+        )
+        await expect(
+          mutate({
+            mutation: sendCoins,
+            variables: {
+              email: 'peter@lustig.de',
+              amount: 30,
+              memo: 'third transaction',
+            },
+          }),
+        ).resolves.toEqual(
+          expect.objectContaining({
+            data: {
+              sendCoins: 'true',
+            },
+          }),
+        )
+        await expect(
+          mutate({
+            mutation: sendCoins,
+            variables: {
+              email: 'peter@lustig.de',
+              amount: 40,
+              memo: 'fourth transaction',
+            },
+          }),
+        ).resolves.toEqual(
+          expect.objectContaining({
+            data: {
+              sendCoins: 'true',
+            },
+          }),
+        )
+      })
+    })
   })
 })
diff --git a/backend/src/graphql/resolver/TransactionResolver.ts b/backend/src/graphql/resolver/TransactionResolver.ts
index 4df7af601..0ac5b382e 100644
--- a/backend/src/graphql/resolver/TransactionResolver.ts
+++ b/backend/src/graphql/resolver/TransactionResolver.ts
@@ -36,6 +36,8 @@ import { BalanceResolver } from './BalanceResolver'
 import { MEMO_MAX_CHARS, MEMO_MIN_CHARS } from './const/const'
 import { findUserByEmail } from './UserResolver'
 
+import { TRANSACTIONS_LOCK } from '@/util/TRANSACTIONS_LOCK'
+
 export const executeTransaction = async (
   amount: Decimal,
   memo: string,
@@ -62,124 +64,133 @@ export const executeTransaction = async (
     throw new Error(`memo text is too short (${MEMO_MIN_CHARS} characters minimum)`)
   }
 
-  // validate amount
-  const receivedCallDate = new Date()
-  const sendBalance = await calculateBalance(
-    sender.id,
-    amount.mul(-1),
-    receivedCallDate,
-    transactionLink,
-  )
-  logger.debug(`calculated Balance=${sendBalance}`)
-  if (!sendBalance) {
-    logger.error(`user hasn't enough GDD or amount is < 0 : balance=${sendBalance}`)
-    throw new Error("user hasn't enough GDD or amount is < 0")
-  }
+  // acquire lock
+  const releaseLock = await TRANSACTIONS_LOCK.acquire()
 
-  const queryRunner = getConnection().createQueryRunner()
-  await queryRunner.connect()
-  await queryRunner.startTransaction('REPEATABLE READ')
-  logger.debug(`open Transaction to write...`)
   try {
-    // transaction
-    const transactionSend = new dbTransaction()
-    transactionSend.typeId = TransactionTypeId.SEND
-    transactionSend.memo = memo
-    transactionSend.userId = sender.id
-    transactionSend.linkedUserId = recipient.id
-    transactionSend.amount = amount.mul(-1)
-    transactionSend.balance = sendBalance.balance
-    transactionSend.balanceDate = receivedCallDate
-    transactionSend.decay = sendBalance.decay.decay
-    transactionSend.decayStart = sendBalance.decay.start
-    transactionSend.previous = sendBalance.lastTransactionId
-    transactionSend.transactionLinkId = transactionLink ? transactionLink.id : null
-    await queryRunner.manager.insert(dbTransaction, transactionSend)
-
-    logger.debug(`sendTransaction inserted: ${dbTransaction}`)
-
-    const transactionReceive = new dbTransaction()
-    transactionReceive.typeId = TransactionTypeId.RECEIVE
-    transactionReceive.memo = memo
-    transactionReceive.userId = recipient.id
-    transactionReceive.linkedUserId = sender.id
-    transactionReceive.amount = amount
-    const receiveBalance = await calculateBalance(recipient.id, amount, receivedCallDate)
-    transactionReceive.balance = receiveBalance ? receiveBalance.balance : amount
-    transactionReceive.balanceDate = receivedCallDate
-    transactionReceive.decay = receiveBalance ? receiveBalance.decay.decay : new Decimal(0)
-    transactionReceive.decayStart = receiveBalance ? receiveBalance.decay.start : null
-    transactionReceive.previous = receiveBalance ? receiveBalance.lastTransactionId : null
-    transactionReceive.linkedTransactionId = transactionSend.id
-    transactionReceive.transactionLinkId = transactionLink ? transactionLink.id : null
-    await queryRunner.manager.insert(dbTransaction, transactionReceive)
-    logger.debug(`receive Transaction inserted: ${dbTransaction}`)
-
-    // Save linked transaction id for send
-    transactionSend.linkedTransactionId = transactionReceive.id
-    await queryRunner.manager.update(dbTransaction, { id: transactionSend.id }, transactionSend)
-    logger.debug(`send Transaction updated: ${transactionSend}`)
-
-    if (transactionLink) {
-      logger.info(`transactionLink: ${transactionLink}`)
-      transactionLink.redeemedAt = receivedCallDate
-      transactionLink.redeemedBy = recipient.id
-      await queryRunner.manager.update(
-        dbTransactionLink,
-        { id: transactionLink.id },
-        transactionLink,
-      )
+    // validate amount
+    const receivedCallDate = new Date()
+    const sendBalance = await calculateBalance(
+      sender.id,
+      amount.mul(-1),
+      receivedCallDate,
+      transactionLink,
+    )
+    logger.debug(`calculated Balance=${sendBalance}`)
+    if (!sendBalance) {
+      logger.error(`user hasn't enough GDD or amount is < 0 : balance=${sendBalance}`)
+      throw new Error("user hasn't enough GDD or amount is < 0")
     }
 
-    await queryRunner.commitTransaction()
-    logger.info(`commit Transaction successful...`)
+    const queryRunner = getConnection().createQueryRunner()
+    await queryRunner.connect()
+    await queryRunner.startTransaction('REPEATABLE READ')
+    logger.debug(`open Transaction to write...`)
+    try {
+      // transaction
+      const transactionSend = new dbTransaction()
+      transactionSend.typeId = TransactionTypeId.SEND
+      transactionSend.memo = memo
+      transactionSend.userId = sender.id
+      transactionSend.linkedUserId = recipient.id
+      transactionSend.amount = amount.mul(-1)
+      transactionSend.balance = sendBalance.balance
+      transactionSend.balanceDate = receivedCallDate
+      transactionSend.decay = sendBalance.decay.decay
+      transactionSend.decayStart = sendBalance.decay.start
+      transactionSend.previous = sendBalance.lastTransactionId
+      transactionSend.transactionLinkId = transactionLink ? transactionLink.id : null
+      await queryRunner.manager.insert(dbTransaction, transactionSend)
 
-    const eventTransactionSend = new EventTransactionSend()
-    eventTransactionSend.userId = transactionSend.userId
-    eventTransactionSend.xUserId = transactionSend.linkedUserId
-    eventTransactionSend.transactionId = transactionSend.id
-    eventTransactionSend.amount = transactionSend.amount.mul(-1)
-    await eventProtocol.writeEvent(new Event().setEventTransactionSend(eventTransactionSend))
+      logger.debug(`sendTransaction inserted: ${dbTransaction}`)
 
-    const eventTransactionReceive = new EventTransactionReceive()
-    eventTransactionReceive.userId = transactionReceive.userId
-    eventTransactionReceive.xUserId = transactionReceive.linkedUserId
-    eventTransactionReceive.transactionId = transactionReceive.id
-    eventTransactionReceive.amount = transactionReceive.amount
-    await eventProtocol.writeEvent(new Event().setEventTransactionReceive(eventTransactionReceive))
-  } catch (e) {
-    await queryRunner.rollbackTransaction()
-    logger.error(`Transaction was not successful: ${e}`)
-    throw new Error(`Transaction was not successful: ${e}`)
-  } finally {
-    await queryRunner.release()
-  }
-  logger.debug(`prepare Email for transaction received...`)
-  await sendTransactionReceivedEmail({
-    firstName: recipient.firstName,
-    lastName: recipient.lastName,
-    email: recipient.emailContact.email,
-    language: recipient.language,
-    senderFirstName: sender.firstName,
-    senderLastName: sender.lastName,
-    senderEmail: sender.emailContact.email,
-    transactionAmount: amount,
-  })
-  if (transactionLink) {
-    await sendTransactionLinkRedeemedEmail({
-      firstName: sender.firstName,
-      lastName: sender.lastName,
-      email: sender.emailContact.email,
-      language: sender.language,
-      senderFirstName: recipient.firstName,
-      senderLastName: recipient.lastName,
-      senderEmail: recipient.emailContact.email,
+      const transactionReceive = new dbTransaction()
+      transactionReceive.typeId = TransactionTypeId.RECEIVE
+      transactionReceive.memo = memo
+      transactionReceive.userId = recipient.id
+      transactionReceive.linkedUserId = sender.id
+      transactionReceive.amount = amount
+      const receiveBalance = await calculateBalance(recipient.id, amount, receivedCallDate)
+      transactionReceive.balance = receiveBalance ? receiveBalance.balance : amount
+      transactionReceive.balanceDate = receivedCallDate
+      transactionReceive.decay = receiveBalance ? receiveBalance.decay.decay : new Decimal(0)
+      transactionReceive.decayStart = receiveBalance ? receiveBalance.decay.start : null
+      transactionReceive.previous = receiveBalance ? receiveBalance.lastTransactionId : null
+      transactionReceive.linkedTransactionId = transactionSend.id
+      transactionReceive.transactionLinkId = transactionLink ? transactionLink.id : null
+      await queryRunner.manager.insert(dbTransaction, transactionReceive)
+      logger.debug(`receive Transaction inserted: ${dbTransaction}`)
+
+      // Save linked transaction id for send
+      transactionSend.linkedTransactionId = transactionReceive.id
+      await queryRunner.manager.update(dbTransaction, { id: transactionSend.id }, transactionSend)
+      logger.debug(`send Transaction updated: ${transactionSend}`)
+
+      if (transactionLink) {
+        logger.info(`transactionLink: ${transactionLink}`)
+        transactionLink.redeemedAt = receivedCallDate
+        transactionLink.redeemedBy = recipient.id
+        await queryRunner.manager.update(
+          dbTransactionLink,
+          { id: transactionLink.id },
+          transactionLink,
+        )
+      }
+
+      await queryRunner.commitTransaction()
+      logger.info(`commit Transaction successful...`)
+
+      const eventTransactionSend = new EventTransactionSend()
+      eventTransactionSend.userId = transactionSend.userId
+      eventTransactionSend.xUserId = transactionSend.linkedUserId
+      eventTransactionSend.transactionId = transactionSend.id
+      eventTransactionSend.amount = transactionSend.amount.mul(-1)
+      await eventProtocol.writeEvent(new Event().setEventTransactionSend(eventTransactionSend))
+
+      const eventTransactionReceive = new EventTransactionReceive()
+      eventTransactionReceive.userId = transactionReceive.userId
+      eventTransactionReceive.xUserId = transactionReceive.linkedUserId
+      eventTransactionReceive.transactionId = transactionReceive.id
+      eventTransactionReceive.amount = transactionReceive.amount
+      await eventProtocol.writeEvent(
+        new Event().setEventTransactionReceive(eventTransactionReceive),
+      )
+    } catch (e) {
+      await queryRunner.rollbackTransaction()
+      logger.error(`Transaction was not successful: ${e}`)
+      throw new Error(`Transaction was not successful: ${e}`)
+    } finally {
+      await queryRunner.release()
+    }
+    logger.debug(`prepare Email for transaction received...`)
+    await sendTransactionReceivedEmail({
+      firstName: recipient.firstName,
+      lastName: recipient.lastName,
+      email: recipient.emailContact.email,
+      language: recipient.language,
+      senderFirstName: sender.firstName,
+      senderLastName: sender.lastName,
+      senderEmail: sender.emailContact.email,
       transactionAmount: amount,
-      transactionMemo: memo,
     })
+    if (transactionLink) {
+      await sendTransactionLinkRedeemedEmail({
+        firstName: sender.firstName,
+        lastName: sender.lastName,
+        email: sender.emailContact.email,
+        language: sender.language,
+        senderFirstName: recipient.firstName,
+        senderLastName: recipient.lastName,
+        senderEmail: recipient.emailContact.email,
+        transactionAmount: amount,
+        transactionMemo: memo,
+      })
+    }
+    logger.info(`finished executeTransaction successfully`)
+    return true
+  } finally {
+    releaseLock()
   }
-  logger.info(`finished executeTransaction successfully`)
-  return true
 }
 
 @Resolver()
diff --git a/backend/src/graphql/resolver/semaphore.test.ts b/backend/src/graphql/resolver/semaphore.test.ts
new file mode 100644
index 000000000..e334910f1
--- /dev/null
+++ b/backend/src/graphql/resolver/semaphore.test.ts
@@ -0,0 +1,190 @@
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
+import Decimal from 'decimal.js-light'
+// eslint-disable-next-line @typescript-eslint/no-unused-vars
+import { logger } from '@test/testSetup'
+import { userFactory } from '@/seeds/factory/user'
+import { bibiBloxberg } from '@/seeds/users/bibi-bloxberg'
+import { bobBaumeister } from '@/seeds/users/bob-baumeister'
+import { peterLustig } from '@/seeds/users/peter-lustig'
+import { creationFactory, nMonthsBefore } from '@/seeds/factory/creation'
+import { cleanDB, testEnvironment, contributionDateFormatter } from '@test/helpers'
+import {
+  confirmContribution,
+  createContribution,
+  createTransactionLink,
+  redeemTransactionLink,
+  login,
+  createContributionLink,
+  sendCoins,
+} from '@/seeds/graphql/mutations'
+
+let mutate: any, con: any
+let testEnv: any
+
+beforeAll(async () => {
+  testEnv = await testEnvironment()
+  mutate = testEnv.mutate
+  con = testEnv.con
+  await cleanDB()
+})
+
+afterAll(async () => {
+  await cleanDB()
+  await con.close()
+})
+
+describe('semaphore', () => {
+  let contributionLinkCode = ''
+  let bobsTransactionLinkCode = ''
+  let bibisTransactionLinkCode = ''
+  let bibisOpenContributionId = -1
+  let bobsOpenContributionId = -1
+
+  beforeAll(async () => {
+    const now = new Date()
+    await userFactory(testEnv, bibiBloxberg)
+    await userFactory(testEnv, peterLustig)
+    await userFactory(testEnv, bobBaumeister)
+    await creationFactory(testEnv, {
+      email: 'bibi@bloxberg.de',
+      amount: 1000,
+      memo: 'Herzlich Willkommen bei Gradido!',
+      creationDate: nMonthsBefore(new Date()),
+      confirmed: true,
+    })
+    await creationFactory(testEnv, {
+      email: 'bob@baumeister.de',
+      amount: 1000,
+      memo: 'Herzlich Willkommen bei Gradido!',
+      creationDate: nMonthsBefore(new Date()),
+      confirmed: true,
+    })
+    await mutate({
+      mutation: login,
+      variables: { email: 'peter@lustig.de', password: 'Aa12345_' },
+    })
+    const {
+      data: { createContributionLink: contributionLink },
+    } = await mutate({
+      mutation: createContributionLink,
+      variables: {
+        amount: new Decimal(200),
+        name: 'Test Contribution Link',
+        memo: 'Danke für deine Teilnahme an dem Test der Contribution Links',
+        cycle: 'ONCE',
+        validFrom: new Date(2022, 5, 18).toISOString(),
+        validTo: new Date(now.getFullYear() + 1, 7, 14).toISOString(),
+        maxAmountPerMonth: new Decimal(200),
+        maxPerCycle: 1,
+      },
+    })
+    contributionLinkCode = 'CL-' + contributionLink.code
+    await mutate({
+      mutation: login,
+      variables: { email: 'bob@baumeister.de', password: 'Aa12345_' },
+    })
+    const {
+      data: { createTransactionLink: bobsLink },
+    } = await mutate({
+      mutation: createTransactionLink,
+      variables: {
+        email: 'bob@baumeister.de',
+        amount: 20,
+        memo: 'Bobs Link',
+      },
+    })
+    const {
+      data: { createContribution: bobsContribution },
+    } = await mutate({
+      mutation: createContribution,
+      variables: {
+        creationDate: contributionDateFormatter(new Date()),
+        amount: 200,
+        memo: 'Bobs Contribution',
+      },
+    })
+    await mutate({
+      mutation: login,
+      variables: { email: 'bibi@bloxberg.de', password: 'Aa12345_' },
+    })
+    const {
+      data: { createTransactionLink: bibisLink },
+    } = await mutate({
+      mutation: createTransactionLink,
+      variables: {
+        amount: 20,
+        memo: 'Bibis Link',
+      },
+    })
+    const {
+      data: { createContribution: bibisContribution },
+    } = await mutate({
+      mutation: createContribution,
+      variables: {
+        creationDate: contributionDateFormatter(new Date()),
+        amount: 200,
+        memo: 'Bibis Contribution',
+      },
+    })
+    bobsTransactionLinkCode = bobsLink.code
+    bibisTransactionLinkCode = bibisLink.code
+    bibisOpenContributionId = bibisContribution.id
+    bobsOpenContributionId = bobsContribution.id
+  })
+
+  it('creates a lot of transactions without errors', async () => {
+    await mutate({
+      mutation: login,
+      variables: { email: 'bibi@bloxberg.de', password: 'Aa12345_' },
+    })
+    const bibiRedeemContributionLink = mutate({
+      mutation: redeemTransactionLink,
+      variables: { code: contributionLinkCode },
+    })
+    const redeemBobsLink = mutate({
+      mutation: redeemTransactionLink,
+      variables: { code: bobsTransactionLinkCode },
+    })
+    const bibisTransaction = mutate({
+      mutation: sendCoins,
+      variables: { email: 'bob@baumeister.de', amount: '50', memo: 'Das ist für dich, Bob' },
+    })
+    await mutate({
+      mutation: login,
+      variables: { email: 'bob@baumeister.de', password: 'Aa12345_' },
+    })
+    const bobRedeemContributionLink = mutate({
+      mutation: redeemTransactionLink,
+      variables: { code: contributionLinkCode },
+    })
+    const redeemBibisLink = mutate({
+      mutation: redeemTransactionLink,
+      variables: { code: bibisTransactionLinkCode },
+    })
+    const bobsTransaction = mutate({
+      mutation: sendCoins,
+      variables: { email: 'bibi@bloxberg.de', amount: '50', memo: 'Das ist für dich, Bibi' },
+    })
+    await mutate({
+      mutation: login,
+      variables: { email: 'peter@lustig.de', password: 'Aa12345_' },
+    })
+    const confirmBibisContribution = mutate({
+      mutation: confirmContribution,
+      variables: { id: bibisOpenContributionId },
+    })
+    const confirmBobsContribution = mutate({
+      mutation: confirmContribution,
+      variables: { id: bobsOpenContributionId },
+    })
+    await expect(bibiRedeemContributionLink).resolves.toMatchObject({ errors: undefined })
+    await expect(redeemBobsLink).resolves.toMatchObject({ errors: undefined })
+    await expect(bibisTransaction).resolves.toMatchObject({ errors: undefined })
+    await expect(bobRedeemContributionLink).resolves.toMatchObject({ errors: undefined })
+    await expect(redeemBibisLink).resolves.toMatchObject({ errors: undefined })
+    await expect(bobsTransaction).resolves.toMatchObject({ errors: undefined })
+    await expect(confirmBibisContribution).resolves.toMatchObject({ errors: undefined })
+    await expect(confirmBobsContribution).resolves.toMatchObject({ errors: undefined })
+  })
+})
diff --git a/backend/src/index.ts b/backend/src/index.ts
index e63f80827..329e63f87 100644
--- a/backend/src/index.ts
+++ b/backend/src/index.ts
@@ -20,6 +20,9 @@ async function main() {
 
   // start DHT hyperswarm when DHT_TOPIC is set in .env
   if (CONFIG.FEDERATION_DHT_TOPIC) {
+    if (CONFIG.FEDERATION_COMMUNITY_URL === null) {
+      throw Error(`Config-Error: missing configuration of property FEDERATION_COMMUNITY_URL`)
+    }
     // eslint-disable-next-line no-console
     console.log(
       `starting Federation on ${CONFIG.FEDERATION_DHT_TOPIC} ${
diff --git a/backend/src/seeds/index.ts b/backend/src/seeds/index.ts
index 3675d381d..9e1939db8 100644
--- a/backend/src/seeds/index.ts
+++ b/backend/src/seeds/index.ts
@@ -75,10 +75,7 @@ const run = async () => {
 
   // create GDD
   for (let i = 0; i < creations.length; i++) {
-    const now = new Date().getTime() // we have to wait a little! quick fix for account sum problem of bob@baumeister.de, (see https://github.com/gradido/gradido/issues/1886)
     await creationFactory(seedClient, creations[i])
-    // eslint-disable-next-line no-empty
-    while (new Date().getTime() < now + 1000) {} // we have to wait a little! quick fix for account sum problem of bob@baumeister.de, (see https://github.com/gradido/gradido/issues/1886)
   }
   logger.info('##seed## seeding all creations successful...')
 
diff --git a/backend/src/util/TRANSACTIONS_LOCK.ts b/backend/src/util/TRANSACTIONS_LOCK.ts
new file mode 100644
index 000000000..847386e4d
--- /dev/null
+++ b/backend/src/util/TRANSACTIONS_LOCK.ts
@@ -0,0 +1,4 @@
+import { Semaphore } from 'await-semaphore'
+
+const CONCURRENT_TRANSACTIONS = 1
+export const TRANSACTIONS_LOCK = new Semaphore(CONCURRENT_TRANSACTIONS)
diff --git a/backend/src/util/validate.ts b/backend/src/util/validate.ts
index 437e04189..397a38730 100644
--- a/backend/src/util/validate.ts
+++ b/backend/src/util/validate.ts
@@ -20,7 +20,7 @@ async function calculateBalance(
   time: Date,
   transactionLink?: dbTransactionLink | null,
 ): Promise<{ balance: Decimal; decay: Decay; lastTransactionId: number } | null> {
-  const lastTransaction = await Transaction.findOne({ userId }, { order: { balanceDate: 'DESC' } })
+  const lastTransaction = await Transaction.findOne({ userId }, { order: { id: 'DESC' } })
   if (!lastTransaction) return null
 
   const decay = calculateDecay(lastTransaction.balance, lastTransaction.balanceDate, time)
diff --git a/backend/yarn.lock b/backend/yarn.lock
index 940906cfa..82bcd6b1f 100644
--- a/backend/yarn.lock
+++ b/backend/yarn.lock
@@ -1643,6 +1643,11 @@ asynckit@^0.4.0:
   resolved "https://registry.yarnpkg.com/asynckit/-/asynckit-0.4.0.tgz#c79ed97f7f34cb8f2ba1bc9790bcc366474b4b79"
   integrity sha1-x57Zf380y48robyXkLzDZkdLS3k=
 
+await-semaphore@^0.1.3:
+  version "0.1.3"
+  resolved "https://registry.yarnpkg.com/await-semaphore/-/await-semaphore-0.1.3.tgz#2b88018cc8c28e06167ae1cdff02504f1f9688d3"
+  integrity sha512-d1W2aNSYcz/sxYO4pMGX9vq65qOTu0P800epMud+6cYYX0QcT7zyqcxec3VWzpgvdXo57UWmVbZpLMjX2m1I7Q==
+
 axios@^0.21.1:
   version "0.21.4"
   resolved "https://registry.yarnpkg.com/axios/-/axios-0.21.4.tgz#c67b90dc0568e5c1cf2b0b858c43ba28e2eda575"
diff --git a/database/entity/0058-add_communities_table/Community.ts b/database/entity/0058-add_communities_table/Community.ts
new file mode 100644
index 000000000..f2d071ce4
--- /dev/null
+++ b/database/entity/0058-add_communities_table/Community.ts
@@ -0,0 +1,42 @@
+import {
+  BaseEntity,
+  Entity,
+  PrimaryGeneratedColumn,
+  Column,
+  CreateDateColumn,
+  UpdateDateColumn,
+} from 'typeorm'
+
+@Entity('communities')
+export class Community extends BaseEntity {
+  @PrimaryGeneratedColumn('increment', { unsigned: true })
+  id: number
+
+  @Column({ name: 'public_key', type: 'binary', length: 64, default: null, nullable: true })
+  publicKey: Buffer
+
+  @Column({ name: 'api_version', length: 10, nullable: false })
+  apiVersion: string
+
+  @Column({ name: 'end_point', length: 255, nullable: false })
+  endPoint: string
+
+  @Column({ name: 'last_announced_at', type: 'datetime', nullable: false })
+  lastAnnouncedAt: Date
+
+  @CreateDateColumn({
+    name: 'created_at',
+    type: 'datetime',
+    default: () => 'CURRENT_TIMESTAMP(3)',
+    nullable: false,
+  })
+  createdAt: Date
+
+  @UpdateDateColumn({
+    name: 'updated_at',
+    type: 'datetime',
+    onUpdate: 'CURRENT_TIMESTAMP(3)',
+    nullable: true,
+  })
+  updatedAt: Date | null
+}
diff --git a/database/entity/Community.ts b/database/entity/Community.ts
new file mode 100644
index 000000000..457d03eae
--- /dev/null
+++ b/database/entity/Community.ts
@@ -0,0 +1 @@
+export { Community } from './0058-add_communities_table/Community'
diff --git a/database/entity/index.ts b/database/entity/index.ts
index a82ef561c..a58afb816 100644
--- a/database/entity/index.ts
+++ b/database/entity/index.ts
@@ -9,6 +9,7 @@ import { UserContact } from './UserContact'
 import { Contribution } from './Contribution'
 import { EventProtocol } from './EventProtocol'
 import { ContributionMessage } from './ContributionMessage'
+import { Community } from './Community'
 
 export const entities = [
   Contribution,
@@ -22,4 +23,5 @@ export const entities = [
   EventProtocol,
   ContributionMessage,
   UserContact,
+  Community,
 ]
diff --git a/database/migrations/0058-add_communities_table.ts b/database/migrations/0058-add_communities_table.ts
new file mode 100644
index 000000000..1e5bb5084
--- /dev/null
+++ b/database/migrations/0058-add_communities_table.ts
@@ -0,0 +1,28 @@
+/* MIGRATION TO CREATE THE FEDERATION COMMUNITY TABLES
+ *
+ * This migration creates the `community` and 'communityfederation' tables in the `apollo` database (`gradido_community`).
+ */
+
+/* eslint-disable @typescript-eslint/explicit-module-boundary-types */
+/* eslint-disable @typescript-eslint/no-explicit-any */
+
+export async function upgrade(queryFn: (query: string, values?: any[]) => Promise<Array<any>>) {
+  await queryFn(`
+    CREATE TABLE communities (
+      id int unsigned NOT NULL AUTO_INCREMENT,
+      public_key binary(64),
+      api_version varchar(10) NOT NULL,
+      end_point varchar(255) NOT NULL,
+      last_announced_at datetime(3) NOT NULL,
+      created_at datetime(3) NOT NULL DEFAULT CURRENT_TIMESTAMP(3),
+      updated_at datetime(3),
+      PRIMARY KEY (id),
+      UNIQUE KEY public_api_key (public_key, api_version)
+    ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;
+  `)
+}
+
+export async function downgrade(queryFn: (query: string, values?: any[]) => Promise<Array<any>>) {
+  // write downgrade logic as parameter of queryFn
+  await queryFn(`DROP TABLE communities;`)
+}