Upgrade a Sharded Cluster to 3.4

Disable the Balancer.

Disable the balancer as described in Disable the Balancer.

Upgrade the config servers.

If the config servers are replica sets:

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

   1. Shut down the secondary mongod instance and replace the 3.2 binary with the 3.4 binary.

   2. Start the 3.4 binary with both the --configsvr and --port options:

      mongod --configsvr --port <port> --dbpath <path>

      If using a configuration file, update the file to specify sharding.clusterRole: configsvr and net.port and start the 3.4 binary:

      sharding:
         clusterRole: configsvr
      net:
         port: <port>
      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, issue rs.status() in the mongo shell.

      Repeat for each secondary member.

2. Step down the replica set primary.

   1. Connect a mongo shell 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 3.4 binary.

   3. Start the 3.4 binary with both the --configsvr and --port options:

      mongod --configsvr --port <port> --dbpath <path>

      If using a configuration file, update the file to specify sharding.clusterRole: configsvr and net.port and start the 3.4 binary:

      sharding:
         clusterRole: configsvr
      net:
         port: <port>
      storage:
         dbpath: <path>

      Include any other configuration as appropriate for your deployment.

Upgrade the shards.

Upgrade the shards one at a time. If the shards are replica sets, for each shard:

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

   1. Shut down the mongod instance and replace the 3.2 binary with the 3.4 binary.

   2. Start the 3.4 binary with the --shardsvr and --port command line options.

      mongod --shardsvr --port <port> --dbpath <path>

      Of if using a configuration file, update the file to include sharding.clusterRole: shardsvr and net.port and start:

      sharding:
         clusterRole: shardsvr
      net:
         port: <port>
      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 the mongo shell.

      Repeat for each secondary member.

2. Step down the replica set primary.

   Connect a mongo shell 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 3.4 binary.

   2. Start the 3.4 binary with the --shardsvr and --port command line options.

      mongod --shardsvr --port <port> --dbpath <path>

      Of if using a configuration file, update the file to specify sharding.clusterRole: shardsvr and net.port and start the 3.4 binary:

      sharding:
         clusterRole: shardsvr
      net:
         port: <port>
      storage:
         dbpath: <path>

      Include any other configuration as appropriate for your deployment.

Upgrade the mongos instances.

Replace each mongos instance with the 3.4 binary and restart. Include any other configuration as appropriate for your deployment.

mongos --configdb csReplSet/<rsconfigsver1:port1>,<rsconfigsver2:port2>,<rsconfigsver3:port3>

Re-enable the balancer.

Using a 3.4 mongo shell, re-enable the balancer as described in Enable the Balancer.

The 3.2 and earlier mongo shell is not compatible with 3.4 clusters.

Enable backwards-incompatible 3.4 features.

At this point, you can run the 3.4 binaries without the 3.4 features that are incompatible with 3.2.

To enable these 3.4 features, set the feature compatibility version to 3.4.

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

db.adminCommand( { setFeatureCompatibilityVersion: "3.4" } )

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.