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initdb.d
initdb.d
 
 
post_scripts
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rs0
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.env
.env
 
 
README.md
README.md
 
 
docker-compose.yml
docker-compose.yml
 
 
docker-run.sh
docker-run.sh
 
 

README.md

MongoDB with ReplicaSet

Example with replicaSet, using three nodes:

  • mongo-rs0-0: node with higher priority to be primary
  • mongo-rs0-1: node usually as secondary
  • mongo-rs0-2: node usually as secondary

The docker-compose instante another service (mongo-setup) to enable the replicaSet. After do this, the container stop.

Run

To prepare the first execution, is necesary create a keyfile and change his permissions (see this for more detail). To simplicate this task, exist the [docker-run.sh] script: if the keyfile doesn't exist, create it, assign the correct permissions, and run the docker-compose.

The next executions, you can start the docker-compose as usual:

docker-compose up

To stop it:

docker-compose stop

To destroy (including volume and network):

docker-compose down

Connect to MongoDB

You can use this connection string:

mongodb://<user>:<pass>@localhost:27017/?replicaSet=<replicaset-name>

When you connect to this port, MongoDB Driver lookup the instances of the replica set and connect against all. The replica set is build based on container IPs, for these reason hasn't problem with name resolution.

This is an example using default .env configuration, using mongo shell as a client:

$ mongo "mongodb://root:example@localhost:27017/?replicaSet=rs0"
MongoDB shell version v4.0.21
connecting to: mongodb://localhost:27017/?gssapiServiceName=mongodb&replicaSet=rs0
2021-01-03T00:50:30.684+0100 I NETWORK  [js] Starting new replica set monitor for rs0/localhost:27017
2021-01-03T00:50:30.686+0100 I NETWORK  [js] Successfully connected to localhost:27017 (1 connections now open to localhost:27017 with a 5 second timeout)
2021-01-03T00:50:30.686+0100 I NETWORK  [js] changing hosts to rs0/172.80.11.2:27017,172.80.11.3:27017,172.80.11.4:27017 from rs0/localhost:27017
2021-01-03T00:50:30.687+0100 I NETWORK  [ReplicaSetMonitor-TaskExecutor] Successfully connected to 172.80.11.2:27017 (1 connections now open to 172.80.11.2:27017 with a 5 second timeout)
2021-01-03T00:50:30.687+0100 I NETWORK  [js] Successfully connected to 172.80.11.4:27017 (1 connections now open to 172.80.11.4:27017 with a 5 second timeout)
2021-01-03T00:50:30.687+0100 I NETWORK  [ReplicaSetMonitor-TaskExecutor] Successfully connected to 172.80.11.3:27017 (1 connections now open to 172.80.11.3:27017 with a 5 second timeout)
Implicit session: session { "id" : UUID("fe10ef9c-0d15-4529-8a0f-a3b2bf01bc2b") }

rs0:PRIMARY> exit

Testing

The services are configured to restart automatically unless stopped using:

docker-compose stop <service-name>

With this configuration, you should test some failover scenarios:

  • Fail one secondary node, stopping the mongo-1 or mongo-2 node
    • ReplicaSet continue running
    • When failed node is started, resync your data from oplog
  • Fail two secondary nodes, stopping the mongo-1 and mongo-2 node
    • ReplicaSet can run as read-only?? or stop all clients??
  • Fail primary node, stopping the mongo-0 node
    • New node elected as primary (mongo-1 or mongo-2)
    • When mongo-0 is started, resync your data from oplog
    • When mongo-0 is restored, and due to higher priority to be primary, will be elected

References