Upgrade a Sharded Cluster to 5.0

Disable the Balancer.

Connect mongosh to a mongos instance in the sharded cluster, and run sh.stopBalancer() to disable the balancer:

sh.stopBalancer()

To verify that the balancer is disabled, run sh.getBalancerState(), which returns false if the balancer is disabled:

sh.getBalancerState()

For more information on disabling the balancer, see Disable the Balancer.

Upgrade the config servers.

1. Upgrade the secondary members of the replica set one at a time:

   1. Shut down the secondary mongod instance and replace the 4.4 binary with the 5.0 binary.

   2. Start the 5.0 binary with the --configsvr, --replSet, and --port. Include any other options as used by the deployment.

      mongod --configsvr --replSet <replSetName> --port <port> --dbpath <path> --bind_ip localhost,<ip address>

      If using a configuration file, update the file to specify sharding.clusterRole: configsvr, replication.replSetName, net.port, and net.bindIp, then start the 5.0 binary:

      sharding:
         clusterRole: configsvr
      replication:
         replSetName: <string>
      net:
         port: <port>
         bindIp: localhost,<ip address>
      storage:
         dbpath: <path>

      Include any other settings as appropriate for your deployment.

   3. Wait for the member to recover to SECONDARY state before upgrading the next secondary member. To check the member's state, issue rs.status() in mongosh.

      Repeat for each secondary member.

2. Step down the replica set primary.

   1. Connect mongosh to the primary and use rs.stepDown() to step down the primary and force an election of a new primary:

      rs.stepDown()

   2. When rs.status() shows that the primary has stepped down and another member has assumed PRIMARY state, shut down the stepped-down primary and replace the mongod binary with the 5.0 binary.

   3. Start the 5.0 binary with the --configsvr, --replSet, --port, and --bind_ip options. Include any optional command line options used by the previous deployment:

      mongod --configsvr --replSet <replSetName> --port <port> --dbpath <path> --bind_ip localhost,<ip address>

      If using a configuration file, update the file to specify sharding.clusterRole: configsvr, replication.replSetName, net.port, and net.bindIp, then start the 5.0 binary:

      sharding:
         clusterRole: configsvr
      replication:
         replSetName: <string>
      net:
         port: <port>
         bindIp: localhost,<ip address>
      storage:
         dbpath: <path>

      Include any other configuration as appropriate for your deployment.

Upgrade the shards.

Upgrade the shards one at a time.

For each shard replica set:

1. Upgrade the secondary members of the replica set one at a time:

   1. Shut down the mongod instance and replace the 4.4 binary with the 5.0 binary.

   2. Start the 5.0 binary with the --shardsvr, --replSet, --port, and --bind_ip options. Include any additional command line options as appropriate for your deployment:

      mongod --shardsvr --replSet <replSetName> --port <port> --dbpath <path> --bind_ip localhost,<ip address>

      If using a configuration file, update the file to include sharding.clusterRole: shardsvr, replication.replSetName, net.port, and net.bindIp, then start the 5.0 binary:

      sharding:
         clusterRole: shardsvr
      replication:
         replSetName: <string>
      net:
         port: <port>
         bindIp: localhost,<ip address>
      storage:
         dbpath: <path>

      Include any other configuration as appropriate for your deployment.

   3. Wait for the member to recover to SECONDARY state before upgrading the next secondary member. To check the member's state, you can issue rs.status() in mongosh.

      Repeat for each secondary member.

2. Step down the replica set primary.

   Connect mongosh to the primary and use rs.stepDown() to step down the primary and force an election of a new primary:

   rs.stepDown()

3. When rs.status() shows that the primary has stepped down and another member has assumed PRIMARY state, upgrade the stepped-down primary:

   1. Shut down the stepped-down primary and replace the mongod binary with the 5.0 binary.

   2. Start the 5.0 binary with the --shardsvr, --replSet, --port, and --bind_ip options. Include any additional command line options as appropriate for your deployment:

      mongod --shardsvr --replSet <replSetName> --port <port> --dbpath <path> --bind_ip localhost,<ip address>

      If using a configuration file, update the file to specify sharding.clusterRole: shardsvr, replication.replSetName, net.port, and net.bindIp, then start the 5.0 binary:

      sharding:
         clusterRole: shardsvr
      replication:
         replSetName: <string>
      net:
         port: <port>
         bindIp: localhost,<ip address>
      storage:
         dbpath: <path>

      Include any other configuration as appropriate for your deployment.

Upgrade the mongos instances.

Replace each mongos instance with the 5.0 binary and restart. Include any other configuration as appropriate for your deployment.

mongos --configdb csReplSet/<rsconfigsver1:port1>,<rsconfigsver2:port2>,<rsconfigsver3:port3> --bind_ip localhost,<ip address>

Re-enable the balancer.

Using mongosh, connect to a mongos in the cluster and run sh.startBalancer() to re-enable the balancer:

sh.startBalancer()

Starting in MongoDB 6.1, automatic chunk splitting is not performed. This is because of balancing policy improvements. Auto-splitting commands still exist, but do not perform an operation. For details, see Balancing Policy Changes.

In MongoDB versions earlier than 6.1, sh.startBalancer() also enables auto-splitting for the sharded cluster.

If you do not wish to enable auto-splitting while the balancer is enabled, you must also run sh.disableAutoSplit().

For more information about re-enabling the balancer, see Enable the Balancer.

Enable backwards-incompatible 5.0 features.

At this point, you can run the 5.0 binaries without the 5.0 features that are incompatible with 4.4.

To enable these 5.0 features, set the feature compatibility version (fCV) to 5.0.

On a mongos instance, run the setFeatureCompatibilityVersion command in the admin database:

db.adminCommand( { setFeatureCompatibilityVersion: "5.0" } )

Setting featureCompatibilityVersion (fCV) : "5.0" implicitly performs a replSetReconfig on each shard to add the term field to the shard replica configuration document and blocks until the new configuration propagates to a majority of replica set members.

This command must perform writes to an internal system collection. If for any reason the command does not complete successfully, you can safely retry the command on the mongos as the operation is idempotent.

Any orphaned documents that exist on your shards will be cleaned up when you set the setFeatureCompatibilityVersion to 5.0. The cleanup process:

• Does not block the upgrade from completing, and

• Is rate limited. To mitigate the potential effect on performance during orphaned document cleanup, see Range Deletion Performance Tuning.