`ServerSelectionTimeoutError` on Dockerized Mongodb Replica Set

[letsgolesco]

I'm trying to use Docker locally to test out mongo-connector but with no luck so far.

It works fine when connecting to a local mongod instance (i.e. just running mongod --replSet singleNodeRepl in terminal), but in Docker I get this error:

ServerSelectionTimeoutError: Could not reach any servers in [(u'344da2f17060', 27017)]. Replica set is configured with internal hostnames or IPs?

For some reason, the IP address of the replica set member inside the Docker container is a hex string: 344da2f17060.

Any way to make this work in Docker?

Following the instructions here, I created a replica set in a docker container (i.e. docker run mongo mongod --replSet singleNodeRepl), executed rs.initiate() from its mongo shell, loaded it up with some data and ran mongo-connector like so:
mongo-connector -c mongo-connector-config.json -m 192.168.99.100:27017 -t 192.168.99.100:9200 -d elastic_doc_manager

The config only contains namespaces.

[aherlihy]

Hello!

Can you send us the mongo-connector logs? Also any and all information about how you're setting up docker would be useful. Thanks!

[kocuroglu]

At one installation, I have faced the same situation. As a workaround, connected to mongo (docker exec -it <mongo docker name> mongo), then run these commands:

cfg = rs.conf()
cfg.members[0].host = "localhost:27017"
rs.reconfig(cfg)

I don't know if this has any downside but looks like working.

[aherlihy]

@letsgolesco Hello, has the workaround above solved your issue?

[robertaistleitner]

I have the same issue, also using docker containers. The fix with localhost:27017 doesn't solve the problem for me, because mongo-connector is running in a different container and hast no idea where localhost:27017 is..

I think the only solution is to use host names which can be resolved by

1. the server where mongodb itself is running on, as well as
2. the server where mongo-connector is running on

because otherwise host name resolution will fail from pymongo library.

This solved the problem for me..

[aherlihy]

Thank you for the workarounds! I have added this issue to the FAQ.

[oxymor0n]

@aherlihy just for future reference, this issue is indeed because mongo-connector cannot resolve the hostnames inside admin.system.replset for the MongoDB cluster. I encounter the same issue with my cluster running on Azure VMs, which was configured to use the internal domain names for the VMs instead of the publicly accessible ones. To fix it, change the hostnames to the ones that can be resolved by mongo-connector using this guide: https://docs.mongodb.com/manual/tutorial/change-hostnames-in-a-replica-set/

[impanda-cookie]

The same issue with docker on mac osx.

Because of mongodb rs.initial() auto assign a random hostname into rs.conf() when i create a default rs mongodb instance.

afdf6a751b18(mongod-3.4.8)[PRIMARY:rs0] admin> rs.conf()
{
  "_id": "rs0",
  "version": 45068,
  "protocolVersion": NumberLong("1"),
  "members": [
    {
      "_id": 0,
      "host": "192.168.99.100:27017", //reset this hostname to docker container ip address 
      "arbiterOnly": false,
      "buildIndexes": true,
      "hidden": false,
      "priority": 1,
      "tags": {

      },
      "slaveDelay": NumberLong("0"),
      "votes": 1
    }
  ],
  "settings": {
    "chainingAllowed": true,
    "heartbeatIntervalMillis": 2000,
    "heartbeatTimeoutSecs": 10,
    "electionTimeoutMillis": 10000,
    "catchUpTimeoutMillis": 60000,
    "getLastErrorModes": {

    },
    "getLastErrorDefaults": {
      "w": 1,
      "wtimeout": 0
    },
    "replicaSetId": ObjectId("59b28470a01cd46654efc5a9")
  }
}

So we can performance rs.reconfig() reset the mongo rs hostname to mongo docker container ip address (in my host default ip address 192.168.99.100 ) it work for me .

[fnordian]

I have the same issue. Strangely it ran for a while, but after rebooting and redeploying the swarm cluster, the error occurred. Can this be fixed instead?
In my setup, mongodb is not reachable under a public ip.

[vancouverwill]

to get this to work on mac (osx has weird config with docker) with locally hosted mongo and mongo-connector in docker we had to add to our mac's hosts file

127.0.0.1 host.docker.internal

Then we updated replica set as stated above so

cfg.members[0].host = "host.docker.internal:27017"

This worked good for us