Port Conflicts when create replication on single server

[Just4test]

Here's part of my docker-compose.yaml:

mongo1:
  image: mongo:4.2
  network_mode: host
  command:  --port 27018 --bind_ip_all --replSet rs0
  environment: 
    MONGO_INITDB_ROOT_USERNAME: ${MONGO_INITDB_ROOT_USERNAME}
    MONGO_INITDB_ROOT_PASSWORD: ${MONGO_INITDB_ROOT_PASSWORD}

mongo2:
  image: mongo:4.2
  network_mode: host
  command:  --port 27019 --bind_ip_all --replSet rs0
  environment: 
    MONGO_INITDB_ROOT_USERNAME: ${MONGO_INITDB_ROOT_USERNAME}
    MONGO_INITDB_ROOT_PASSWORD: ${MONGO_INITDB_ROOT_PASSWORD}

mongo2:
  image: mongo:4.2
  network_mode: host
  command:  --port 27020 --bind_ip_all --replSet rs0
  environment: 
    MONGO_INITDB_ROOT_USERNAME: ${MONGO_INITDB_ROOT_USERNAME}
    MONGO_INITDB_ROOT_PASSWORD: ${MONGO_INITDB_ROOT_PASSWORD}

When I run docker-compose up, some times sevel container boot crash.

2020-11-26T07:59:10.584+0000 I  CONTROL  [initandlisten] options: { net: { bindIp: "127.0.0.1", port: 27017, tls: { mode: "disabled" } }, processManagement: { fork: true, pidFilePath: "/tmp/docker-entrypoint-temp-mongod.pid" }, security: { keyFile: "/mongodb.key" }, systemLog: { destination: "file", logAppend: true, path: "/proc/1/fd/1", quiet: true } }
2020-11-26T07:59:10.585+0000 E  STORAGE  [initandlisten] Failed to set up listener: SocketException: Address already in use
......
2020-11-26T07:59:10.585+0000 I  CONTROL  [initandlisten] shutting down with code:48

That's because container will create a mongod init process which always using port 27017. The init process will last for about one second. If sevel mongo container boot at the same time, Only one init process can bind 27017, other will crash.

[wglambert]

If you're using the host network mode then you'll have to stagger the initializations or pre-initialize them as the entrypoint will temporarily be listening on 27017

mongo/4.4/docker-entrypoint.sh

Lines 240 to 247 in da7e52d

	if [ -n "$shouldPerformInitdb" ]; then
	mongodHackedArgs=( "$@" )
	if _parse_config "$@"; then
	_mongod_hack_ensure_arg_val --config "$tempConfigFile" "${mongodHackedArgs[@]}"
	fi
	_mongod_hack_ensure_arg_val --bind_ip 127.0.0.1 "${mongodHackedArgs[@]}"
	_mongod_hack_ensure_arg_val --port 27017 "${mongodHackedArgs[@]}"
	_mongod_hack_ensure_no_arg --bind_ip_all "${mongodHackedArgs[@]}"

There was also a lengthy discussion on replicasets here #246

[tianon]

There's a potential solution to this over in #443. 👀