Can't connect to MongoDB with Replica Set running as a container in localhost

Question

This is a fairly simple scenario and I cannot figure out why it's not working.

I have a docker compose

version: '3.8'

services:
  mongodb:
    image: mongo:latest
    command: ["mongod", "--replSet", "rs0", "--bind_ip_all"]
    ports:
      - "27017:27017"

I run docker-compose up to spin it up

And I can see some logs

sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:26.001+00:00"},"s":"W",  "c":"QUERY",    "id":23799,   "ctx":"ftdc","msg":"Aggregate command executor error","attr":{"error":{"code":26,"codeName":"NamespaceNotFound","errmsg":"Unable to retrieve storageStats in $collStats stage :: caused by :: Collection [local.oplog.rs] not found."},"stats":{},"cmd":{"aggregate":"oplog.rs","cursor":{},"pipeline":[{"$collStats":{"storageStats":{"waitForLock":false,"numericOnly":true}}}],"$db":"local"}}}
sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:26.128+00:00"},"s":"I",  "c":"-",        "id":4939300, "ctx":"monitoring-keys-for-HMAC","msg":"Failed to refresh key cache","attr":{"error":"ReadConcernMajorityNotAvailableYet: Read concern majority reads are currently not possible.","nextWakeupMillis":800}}
sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:26.929+00:00"},"s":"I",  "c":"-",        "id":4939300, "ctx":"monitoring-keys-for-HMAC","msg":"Failed to refresh key cache","attr":{"error":"ReadConcernMajorityNotAvailableYet: Read concern majority reads are currently not possible.","nextWakeupMillis":1000}}
sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:27.001+00:00"},"s":"W",  "c":"QUERY",    "id":23799,   "ctx":"ftdc","msg":"Aggregate command executor error","attr":{"error":{"code":26,"codeName":"NamespaceNotFound","errmsg":"Unable to retrieve storageStats in $collStats stage :: caused by :: Collection [local.oplog.rs] not found."},"stats":{},"cmd":{"aggregate":"oplog.rs","cursor":{},"pipeline":[{"$collStats":{"storageStats":{"waitForLock":false,"numericOnly":true}}}],"$db":"local"}}}
sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:27.930+00:00"},"s":"I",  "c":"-",        "id":4939300, "ctx":"monitoring-keys-for-HMAC","msg":"Failed to refresh key cache","attr":{"error":"ReadConcernMajorityNotAvailableYet: Read concern majority reads are currently not possible.","nextWakeupMillis":1200}}
sandbox-mongodb-1  | {"t":{"$date":"2023-12-21T18:46:28.001+00:00"},"s":"W",  "c":"QUERY",    "id":23799,   "ctx":"ftdc","msg":"Aggregate command executor error","attr":{"error":{"code":26,"codeName":"NamespaceNotFound","errmsg":"Unable to retrieve storageStats in $collStats stage :: caused by :: Collection [local.oplog.rs] not found."},"stats":{},"cmd":{"aggregate":"oplog.rs","cursor":{},"pipeline":[{"$collStats":{"storageStats":{"waitForLock":false,"numericOnly":true}}}],"$db":"local"}}}

Now I do a

docker ps

and I can see the container Id

$ docker ps
CONTAINER ID   IMAGE          COMMAND                  CREATED          STATUS          PORTS                      NAMES
fdea0af9dc8e   mongo:latest   "docker-entrypoint.s…"   12 minutes ago   Up 12 minutes   0.0.0.0:27017->27017/tcp   sandbox-mongodb-1

I can connect to it with mongosh

$ docker exec -it 5d44bda7d148 mongosh
Current Mongosh Log ID: 658488458e2ace9369e0f846
Connecting to:          mongodb://127.0.0.1:27017/?directConnection=true&serverSelectionTimeoutMS=2000&appName=mongosh+2.1.1
Using MongoDB:          7.0.4
Using Mongosh:          2.1.1

For mongosh info see: https://docs.mongodb.com/mongodb-shell/


To help improve our products, anonymous usage data is collected and sent to MongoDB periodically (https://www.mongodb.com/legal/privacy-policy).
You can opt-out by running the disableTelemetry() command.

------
   The server generated these startup warnings when booting
   2023-12-21T18:46:24.293+00:00: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine. See http://dochub.mongodb.org/core/prodnotes-filesystem
   2023-12-21T18:46:24.911+00:00: Access control is not enabled for the database. Read and write access to data and configuration is unrestricted
   2023-12-21T18:46:24.911+00:00: /sys/kernel/mm/transparent_hugepage/enabled is 'always'. We suggest setting it to 'never'
   2023-12-21T18:46:24.911+00:00: vm.max_map_count is too low
------

I initialize the replica set

test> rs.initiate()
{
  info2: 'no configuration specified. Using a default configuration for the set',
  me: '5d44bda7d148:27017',
  ok: 1
}

And I can see current config

rs0 [direct: other] test> rs.config()
{
  _id: 'rs0',
  version: 1,
  term: 1,
  members: [
    {
      _id: 0,
      host: '5d44bda7d148:27017',
      arbiterOnly: false,
      buildIndexes: true,
      hidden: false,
      priority: 1,
      tags: {},
      secondaryDelaySecs: Long('0'),
      votes: 1
    }
  ],
  protocolVersion: Long('1'),
  writeConcernMajorityJournalDefault: true,
  settings: {
    chainingAllowed: true,
    heartbeatIntervalMillis: 2000,
    heartbeatTimeoutSecs: 10,
    electionTimeoutMillis: 10000,
    catchUpTimeoutMillis: -1,
    catchUpTakeoverDelayMillis: 30000,
    getLastErrorModes: {},
    getLastErrorDefaults: { w: 1, wtimeout: 0 },
    replicaSetId: ObjectId('6584887336c122ec814c9914')
  }
}

Now I open, on my host (Windows) 3T studio and I create connections.

This connection string works well

mongodb://127.0.0.1:27017

This connection string does not connect

mongodb://127.0.0.1:27017/?replicaSet=rs0&ssl=false

Why?

Apparently the replica set is running properly and it's obvious I can reach the server

This is the timeout error 3T Studio shows

SERVER [5d44bda7d148:27017] (Type: UNKNOWN) 
|_/ Connection error (MongoSocketOpenException): Exception opening socket
|____/ Unknown host: 5d44bda7d148

Details:
Timed out after 30000 ms while waiting for a server that matches com.mongodb.client.internal.MongoClientDelegate$1@482d37d9. Client view of cluster state is {type=REPLICA_SET, servers=[{address=5d44bda7d148:27017, type=UNKNOWN, state=CONNECTING, exception={com.mongodb.MongoSocketOpenException: Exception opening socket}, caused by {java.net.UnknownHostException: 5d44bda7d148}}]

I need to have MongoDb replica set running as a docker container locally, because I need it for local development with change streams. I'd appreciate an explanation and a solution.

---

UPDATE 1 (2023-12-21) I have also tried with

command: ["mongod", "--replSet", "rs0", "--bind_ip", "localhost"]

in docker compose, as per https://www.mongodb.com/docs/manual/tutorial/deploy-replica-set/#ip-binding but no luck

Answer 1

It seems the problem was with the host that the replica set is configured by default. It seems to pick the container ID, which is not what I want.

If I connect with mongosh and do this:

let cfg = rs.config()
cfg.members[0].host = 'localhost:27017'
rs.reconfig(cfg)

essentially modifying the host so that now it looks like

rs0 [direct: primary] test> rs.config()
{
  _id: 'rs0',
  version: 3,
  term: 1,
  members: [
    {
      _id: 0,
      host: '127.0.0.1:27017',
      arbiterOnly: false,
      buildIndexes: true,
      hidden: false,
      priority: 1,
      tags: {},
      secondaryDelaySecs: Long('0'),
      votes: 1
    }
  ],
  protocolVersion: Long('1'),
  writeConcernMajorityJournalDefault: true,
  settings: {
    chainingAllowed: true,
    heartbeatIntervalMillis: 2000,
    heartbeatTimeoutSecs: 10,
    electionTimeoutMillis: 10000,
    catchUpTimeoutMillis: -1,
    catchUpTakeoverDelayMillis: 30000,
    getLastErrorModes: {},
    getLastErrorDefaults: { w: 1, wtimeout: 0 },
    replicaSetId: ObjectId('6584bfe7812f7983ae2da944')
  }
}

I can now connect from my host to

mongodb://localhost:27017/?replicaSet=rs0

It feels hacky, but it seems to work.

---

UPDATE

Another cleaner option would be to connect to mongosh and do this instead, to pass configuration without having to reconfigure

test> const configuration = { _id: "rs0", members: [{ _id: 0, host: "127.0.0.1:27017"}]}

test> rs.initiate(configuration)

which gives me a similar result in which the host has 127.0.0.1 or localhost instead of the container id.