configure-a-replica-set-for-mongodb.md

Configure a Replica Set for MongoDB

Rocket.Chat uses the MongoDB replica set to improve performance via Meteor Oplog tailing. Replica sets are used to provide high data availability by maintaining multiple copies of the data across different servers.

{% hint style="info" %} Check the release notes to ensure you are using a compatible version of MongoDB. {% endhint %}

To configure the replica set, add this section to the mongod.conf file:

replication: // indicates the beginning of the replication configuration section
  replSetName: "rs01"

For example, run the following command to update the replication settings in the MongoDB configuration file:

echo -e "replication:\n  replSetName: \"rs01\"" | sudo tee -a /etc/mongod.conf

Restart MongoDB and initiate the replica set

Follow these steps to initiate the MongoDB replica set:

1. Restart MongoDB service:

sudo systemctl restart mongod

2. Start the MongoDB shell and initiate the replica set:

mongo
> rs.initiate()

The output of the command should look like this:

{
    "info2" : "no configuration specified. Using a default configuration for the set",
    "me" : "127.0.0.1:27017",
    "ok" : 1,
    "operationTime" : Timestamp(1538772048, 1),
    "$clusterTime" : {
        "clusterTime" : Timestamp(1538772048, 1),
        "signature" : {
            "hash" : BinData(0,"AAAAAAAAAAAAAAAAAAAAAAAAAAA="),
            "keyId" : NumberLong(0)
        }
    }
}
rs01:SECONDARY>

Note that the ok value should be 1. Any other value, i.e. 93, means something is wrong.

3. Hit enter, you should see your prompt turn into rs01:PRIMARY>, this indicates the replica set is being used. Type exit to get back to your regular shell:

rs01:PRIMARY> exit
bye

Troubleshooting

Depending on your network settings, including /etc/hosts and DNS, if you have configured Rocket.Chat to use localhost:27017, you may see an error similar to this:

{% code overflow="wrap" %}

[conn1] created this configuration for initiation : { _id: "rs0", version: 1, members: [ { _id: 0, host: "test:27017" } ] }

{% endcode %}

rs.initiate() may be defaulting to the host name e.g., test.

You can force a different hostname as follows:

rs.initiate({ _id: 'rs01', members: [ { _id: 0, host: 'localhost:27017' } ]})

You should get a response similar to the following:

> rs.initiate({ _id: 'rs01', members: [ { _id: 0, host: 'localhost:27017' } ]})
{ "ok" : 1 }
rs0:OTHER>

Reconfigure and restart Rocket.Chat service

After you configured the replica set, you must add the MONGO_OPLOG_URL environment variable to the service definition and restart Rocket.Chat server.

• In CentOS, open the file /usr/lib/systemd/system/rocketchat.service
• In Ubuntu or Debian, open the file /lib/systemd/system/rocketchat.service

Add the following to the environment line:

MONGO_OPLOG_URL=mongodb://localhost:27017/local?replSet=rs01

Reload the system state and restart Rocket.Chat:

sudo systemctl daemon-reload && sudo systemctl restart rocketchat