How do i connect a simple node.js app running on docker to a Open Policy Server also running on a docker container

Question

I'm trying to bundle together a node app and a Open Policy Agent server using docker compose, i can access the OPA server from my browser but when i tried to to a request using axios from the node app i get this:

Error: connect ECONNREFUSED 127.0.0.1:8181
    at TCPConnectWrap.afterConnect [as oncomplete] (net.js:1159:16) {
  errno: -111,
  code: 'ECONNREFUSED',
  syscall: 'connect',
  address: '127.0.0.1',
  port: 8181,
  config: {
    transitional: {
      silentJSONParsing: true,
      forcedJSONParsing: true,
      clarifyTimeoutError: false
    },
    adapter: [Function: httpAdapter],
    transformRequest: [ [Function: transformRequest] ],
    transformResponse: [ [Function: transformResponse] ],
    timeout: 0,
    xsrfCookieName: 'XSRF-TOKEN',
    xsrfHeaderName: 'X-XSRF-TOKEN',
    maxContentLength: -1,
    maxBodyLength: -1,
    validateStatus: [Function: validateStatus],
    headers: {
      Accept: 'application/json, text/plain, */*',
      'User-Agent': 'axios/0.26.0'
    },
    method: 'get',
    url: 'http://localhost:8181',
    data: undefined
  },
  request: <ref *1> Writable {
    _writableState: WritableState {
      objectMode: false,
      highWaterMark: 16384,
      finalCalled: false,
      needDrain: false,
      ending: false,
      ended: false,
      finished: false,
      destroyed: false,
      decodeStrings: true,
      defaultEncoding: 'utf8',
      length: 0,
      writing: false,
      corked: 0,
      sync: true,
      bufferProcessing: false,
      onwrite: [Function: bound onwrite],
      writecb: null,
      writelen: 0,
      afterWriteTickInfo: null,
      buffered: [],
      bufferedIndex: 0,
      allBuffers: true,
      allNoop: true,
      pendingcb: 0,
      prefinished: false,
      errorEmitted: false,
      emitClose: true,
      autoDestroy: true,
      errored: null,
      closed: false
    },
    _events: [Object: null prototype] {
      response: [Function: handleResponse],
      error: [Function: handleRequestError],
      socket: [Function: handleRequestSocket]
    },
    _eventsCount: 3,
    _maxListeners: undefined,
    _options: {
      maxRedirects: 21,
      maxBodyLength: 10485760,
      protocol: 'http:',
      path: '/',
      method: 'GET',
      headers: [Object],
      agent: undefined,
      agents: [Object],
      auth: undefined,
      hostname: 'localhost',
      port: '8181',
      nativeProtocols: [Object],
      pathname: '/'
    },
    _ended: true,
    _ending: true,
    _redirectCount: 0,
    _redirects: [],
    _requestBodyLength: 0,
    _requestBodyBuffers: [],
    _onNativeResponse: [Function (anonymous)],
    _currentRequest: ClientRequest {
      _events: [Object: null prototype],
      _eventsCount: 7,
      _maxListeners: undefined,
      outputData: [],
      outputSize: 0,
      writable: true,
      destroyed: false,
      _last: true,
      chunkedEncoding: false,
      shouldKeepAlive: false,
      _defaultKeepAlive: true,
      useChunkedEncodingByDefault: false,
      sendDate: false,
      _removedConnection: false,
      _removedContLen: false,
      _removedTE: false,
      _contentLength: 0,
      _hasBody: true,
      _trailer: '',
      finished: true,
      _headerSent: true,
      socket: [Socket],
      _header: 'GET / HTTP/1.1\r\n' +
        'Accept: application/json, text/plain, */*\r\n' +
        'User-Agent: axios/0.26.0\r\n' +
        'Host: localhost:8181\r\n' +
        'Connection: close\r\n' +
        '\r\n',
      _keepAliveTimeout: 0,
      _onPendingData: [Function: noopPendingOutput],
      agent: [Agent],
      socketPath: undefined,
      method: 'GET',
      maxHeaderSize: undefined,
      insecureHTTPParser: undefined,
      path: '/',
      _ended: false,
      res: null,
      aborted: false,
      timeoutCb: null,
      upgradeOrConnect: false,
      parser: null,
      maxHeadersCount: null,
      reusedSocket: false,
      host: 'localhost',
      protocol: 'http:',
      _redirectable: [Circular *1],
      [Symbol(kCapture)]: false,
      [Symbol(kNeedDrain)]: false,
      [Symbol(corked)]: 0,
      [Symbol(kOutHeaders)]: [Object: null prototype]
    },
    _currentUrl: 'http://localhost:8181/',
    [Symbol(kCapture)]: false
  },
  response: undefined,
  isAxiosError: true,
  toJSON: [Function: toJSON]
}

I also tried to run 2 node app with the same results so the opa servers is no the problem

I created an.network and make sure both containers are part of it:

$ docker network inspect -f '{{range .Containers}}{{.Name}} {{end}}' opa_network
result: opa-nodejs_client_1 opa-nodejs_server_1 


$ docker exec opa-nodejs_client_1 ping opa-nodejs_server_1 -c2
Result: PING opa-nodejs_server_1 (172.31.0.3) 56(84) bytes of data.
64 bytes from opa-nodejs_server_1.opa_network (172.31.0.3): icmp_seq=1 ttl=64 time=0.065 ms
64 bytes from opa-nodejs_server_1.opa_network (172.31.0.3): icmp_seq=2 ttl=64 time=0.128 ms

--- opa-nodejs_server_1 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1023ms
rtt min/avg/max/mdev = 0.065/0.096/0.128/0.033 ms

this is the docker compose file:

version: '3.9'
services:
    server:
        build: 
            dockerfile: Dockerfile
            context: ./OPA
        ports: 
        - 8181:8181
        networks:
        - opa_network  
    client: 
        build: 
            dockerfile: Dockerfile
            context: ./nodejs_google_auth
        ports: 
        - 3000:3000
        networks:
        - opa_network

networks:
  opa_network:
    external: true

Answer 1

thanks, i found the solution, each docker container has its own ip address, so i had to use the ip address of the server container instead of "localhost"