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Upgrade MongoDB to 3.0

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In the general case, the upgrade from MongoDB 2.6 to 3.0 is a binary-compatible “drop-in” upgrade: shut down the mongod instances and replace them with mongod instances running 3.0. However, before you attempt any upgrade please familiarize yourself with the content of this document, particularly the procedure for upgrading sharded clusters.

If you need guidance on upgrading to 3.0, MongoDB offers consulting to help ensure a smooth transition without interruption to your MongoDB application.

Upgrade Recommendations and Checklists

When upgrading, consider the following:

Upgrade Requirements

To upgrade an existing MongoDB deployment to 3.0, you must be running 2.6. If you’re running a version of MongoDB before 2.6, you must upgrade to 2.6 before upgrading to 3.0. See Upgrade to 2.6 for the procedure to upgrade from 2.4 to 2.6. Once upgraded to MongoDB 2.6, you cannot downgrade to any version earlier than MongoDB 2.4.

If your existing MongoDB deployment is already running with authentication and authorization, your user data model authSchema must be at least version 3. To verify the version of your existing authSchema, see MongoDB 2.4 User Model Removed. To upgrade your authSchema version, see Upgrade Authorization Data for details.

Preparedness

Before upgrading MongoDB, always test your application in a staging environment before deploying the upgrade to your production environment.

Some changes in MongoDB 3.0 require manual checks and intervention. Before beginning your upgrade, see the Compatibility Changes in MongoDB 3.0 document to ensure that your applications and deployments are compatible with MongoDB 3.0. Resolve the incompatibilities in your deployment before starting the upgrade.

Downgrade Limitations

Once upgraded to MongoDB 3.0, you cannot downgrade to a version lower than 2.6.8.

If you upgrade to 3.0 and have run authSchemaUpgrade, you cannot downgrade to 2.6 without disabling --auth or restoring a pre-upgrade backup, as authSchemaUpgrade discards the MONGODB-CR credentials used in 2.6. See Upgrade Existing MONGODB-CR Users to Use SCRAM-SHA-1.

Upgrade MongoDB Processes

Upgrade Standalone mongod Instance to MongoDB 3.0

The following steps outline the procedure to upgrade a standalone mongod from version 2.6 to 3.0. To upgrade from version 2.4 to 3.0, upgrade to version 2.6 first, and then use the following procedure to upgrade from 2.6 to 3.0.

Upgrade Binaries

If you installed MongoDB from the MongoDB apt, yum, or zypper repositories, you should upgrade to 3.0 using your package manager. Follow the appropriate installation instructions for your Linux system. This will involve adding a repository for the new release, then performing the actual upgrade.

Otherwise, you can manually upgrade MongoDB:

1
Download 3.0 binaries.

Download binaries of the latest release in the 3.0 series from the MongoDB Download Page. See Install MongoDB for more information.

2
Replace 2.6 binaries.

Shut down your mongod instance. Replace the existing binary with the 3.0 mongod binary and restart mongod.

Change Storage Engine for Standalone to WiredTiger

To change the storage engine for a standalone mongod instance to WiredTiger, see Change Standalone to WiredTiger.

Upgrade a Replica Set to 3.0

Prerequisites

  • If the oplog contains entries generated by versions of MongoDB that precede version 2.2.1, you must wait for the entries to be overwritten by later versions before you can upgrade to MongoDB 3.0. For more information, see Replica Set Oplog Format Change
  • Stricter validation in MongoDB 3.0 of replica set configuration may invalidate previously-valid replica set configuration, preventing replica sets from starting in MongoDB 3.0. For more information, see Replica Set Configuration Validation.
  • All replica set members must be running version 2.6 before you can upgrade them to version 3.0. To upgrade a replica set from an earlier MongoDB version, upgrade all members of the replica set to version 2.6 first, and then follow the procedure to upgrade from MongoDB 2.6 to 3.0.

Upgrade Binaries

You can upgrade from MongoDB 2.6 to 3.0 using a “rolling” upgrade to minimize downtime by upgrading the members individually while the other members are available:

1
Upgrade secondary members of the replica set.

Upgrade the secondary members of the set one at a time by shutting down the mongod and replacing the 2.6 binary with the 3.0 binary. After upgrading a mongod instance, wait for the member to recover to SECONDARY state before upgrading the next instance. To check the member’s state, issue rs.status() in the mongo shell.

2
Step down the replica set primary.

Use rs.stepDown() in the mongo shell to step down the primary and force the set to failover. rs.stepDown() expedites the failover procedure and is preferable to shutting down the primary directly.

3
Upgrade the primary.

When rs.status() shows that the primary has stepped down and another member has assumed PRIMARY state, shut down the previous primary and replace the mongod binary with the 3.0 binary and start the new instance.

Replica set failover is not instant and will render the set unavailable to accept writes until the failover process completes. This may take 30 seconds or more: schedule the upgrade procedure during a scheduled maintenance window.

Change Replica Set Storage Engine to WiredTiger

To change the storage engine for a replica set to WiredTiger, see Change Replica Set to WiredTiger.

Upgrade a Sharded Cluster to 3.0

Only upgrade sharded clusters to 3.0 if all members of the cluster are currently running instances of 2.6. The only supported upgrade path for sharded clusters running 2.4 is via 2.6. The upgrade process checks all components of the cluster and will produce warnings if any component is running version 2.4.

Considerations

The upgrade process does not require any downtime. However, while you upgrade the sharded cluster, ensure that clients do not make changes to the collection meta-data. For example, during the upgrade, do not do any of the following:

Upgrade Sharded Clusters

Optional but Recommended. As a precaution, take a backup of the config database before upgrading the sharded cluster.

1
Disable the Balancer.

Turn off the balancer in the sharded cluster, as described in Disable the Balancer.

2
Upgrade the cluster’s meta data.

Start a single 3.0 mongos instance with the configDB pointing to the cluster’s config servers and with the --upgrade option.

To run a mongos with the --upgrade option, you can upgrade an existing mongos instance to 3.0, or if you need to avoid reconfiguring a production mongos instance, you can use a new 3.0 mongos that can reach all the config servers.

To upgrade the meta data, run:

copy 
mongos --configdb <configDB string> --upgrade

You can include the --logpath option to output the log messages to a file instead of the standard output. Also include any other options required to start mongos instances in your cluster, such as --sslOnNormalPorts or --sslPEMKeyFile.

The 3.0 mongos will output informational log messages.

copy 
<timestamp> I SHARDING [mongosMain] MongoS version 3.0.0 starting: ...
...
<timestamp> I SHARDING [mongosMain] starting upgrade of config server from v5 to v6
<timestamp> I SHARDING [mongosMain] starting next upgrade step from v5 to v6
<timestamp> I SHARDING [mongosMain] about to log new metadata event: ...
<timestamp> I SHARDING [mongosMain] checking that version of host ... is compatible with 2.6
...
<timestamp> I SHARDING [mongosMain] upgrade of config server to v6 successful
...
<timestamp> I SHARDING [mongosMain] distributed lock 'configUpgrade/...' unlocked.
<timestamp> I -        [mongosMain] Config database is at version v6

The mongos will exit upon completion of the --upgrade process.

The upgrade will prevent any chunk moves or splits from occurring during the upgrade process. If the data files have many sharded collections or if failed processes hold stale locks, acquiring the locks for all collections can take seconds or minutes. Watch the log for progress updates.

3
Ensure mongos --upgrade process completes successfully.

The mongos will exit upon completion of the meta data upgrade process. If successful, the process will log the following messages:

copy 
<timestamp> I SHARDING [mongosMain] upgrade of config server to v6 successful
...
<timestamp> I -        [mongosMain] Config database is at version v6

After a successful upgrade, restart the mongos instance. If mongos fails to start, check the log for more information.

If the mongos instance loses its connection to the config servers during the upgrade or if the upgrade is otherwise unsuccessful, you may always safely retry the upgrade.

4
Upgrade the remaining mongos instances to 3.0.

Upgrade and restart without the --upgrade option the other mongos instances in the sharded cluster.

After you have successfully upgraded all mongos instances, you can proceed to upgrade the other components in your sharded cluster.

Warning

Do not upgrade the mongod instances until after you have upgraded all the mongos instances.

5
Upgrade the config servers.

After you have successfully upgraded all mongos instances, upgrade all 3 mongod config server instances, leaving the first config server listed in the mongos --configdb argument to upgrade last.

6
Upgrade the shards.

Upgrade each shard, one at a time, upgrading the mongod secondaries before running replSetStepDown and upgrading the primary of each shard.

7
Re-enable the balancer.

Once the upgrade of sharded cluster components is complete, Re-enable the balancer.

Change Sharded Cluster Storage Engine to WiredTiger

For a sharded cluster in MongoDB 3.0, you can choose to update the shards to use WiredTiger storage engine and have the config servers use MMAPv1. If you update the config servers to use WiredTiger, you must update all three config servers to use WiredTiger.

To change a sharded cluster to use WiredTiger, see Change Sharded Cluster to WiredTiger.

Upgrade Existing MONGODB-CR Users to Use SCRAM-SHA-1

After upgrading the binaries, see Upgrade to SCRAM for details on SCRAM-SHA-1 upgrade scenarios.

General Upgrade Procedure

Except as described on this page, moving between 2.6 and 3.0 is a drop-in replacement:

1

Stop the existing mongod instance.

For example, on Linux, run 2.6 mongod with the --shutdown option as follows:

copy 
mongod --dbpath /var/mongod/data --shutdown

Replace /var/mongod/data with your MongoDB dbPath. See also the Stop mongod Processes for alternate methods of stopping a mongod instance.

2

Start the new mongod instance.

Ensure you start the 3.0 mongod with the same dbPath:

copy 
mongod --dbpath /var/mongod/data

Replace /var/mongod/data with your MongoDB dbPath.

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