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Upgrade a Replica Set to 4.4

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Warning

When upgrading a MongoDB 4.2-series deployment containing MongoDB 3.0 metadata to a 4.4-series deployment, you must upgrade to MongoDB 4.4.1 or later. You cannot successfully upgrade a deployment containing MongoDB 3.0 metadata to MongoDB 4.4.0 without serious risk of downtime.

For more information, see WT-6623.

Familiarize yourself with the content of this document, including thoroughly reviewing the prerequisites, prior to upgrading to MongoDB 4.4.

If you need guidance on upgrading to 4.4, MongoDB offers major version upgrade services to help ensure a smooth transition without interruption to your MongoDB application.

Upgrade Recommendations and Checklists

When upgrading, consider the following:

Upgrade Version Path

To upgrade an existing MongoDB deployment to 4.4, you must be running a 4.2-series release.

To upgrade from a version earlier than the 4.2-series, you must successively upgrade major releases until you have upgraded to 4.2-series. For example, if you are running a 4.0-series, you must upgrade first to 4.2 before you can upgrade to 4.4.

Preparedness

Before beginning your upgrade, see the Compatibility Changes in MongoDB 4.4 document to ensure that your applications and deployments are compatible with MongoDB 4.4. Resolve the incompatibilities in your deployment before starting the upgrade.

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

Downgrade Consideration

Once upgraded to 4.4, if you need to downgrade, we recommend downgrading to the latest patch release of 4.2.

Downgrade Floor

If you need to downgrade form version 4.4, downgrade to 4.2.6 or a later version. You cannot downgrade to 4.2.5 or an earlier version.

Prerequisites

All Members Version

All replica set members must be running version 4.2. To upgrade a replica set from an 4.0-series and earlier, first upgrade all members of the replica set to the latest 4.2-series release, and then follow the procedure to upgrade from MongoDB 4.2 to 4.4.

Confirm Clean Shutdown

Prior to upgrading a member of the replica set, confirm that the member was cleanly shut down.

Feature Compatibility Version

The 4.2 replica set must have featureCompatibilityVersion set to "4.2".

To ensure that all members of the replica set have featureCompatibilityVersion set to "4.2", connect to each replica set member and check the featureCompatibilityVersion:

copy 
db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )

All members should return a result that includes "featureCompatibilityVersion" : { "version" : "4.2" }.

To set or update featureCompatibilityVersion, run the following command on the primary. A majority of the data-bearing members must be available:

copy 
db.adminCommand( { setFeatureCompatibilityVersion: "4.2" } )

For more information, see setFeatureCompatibilityVersion.

Replica Set Member State

Ensure that no replica set member is in ROLLBACK or RECOVERING state.

Download 4.4 Binaries

Via Package Manager

If you installed MongoDB from the MongoDB apt, yum, dnf, or zypper repositories, you should upgrade to 4.4 using your package manager.

Follow the appropriate 4.4 installation instructions for your Linux system. This will involve adding a repository for the new release, then performing the actual upgrade process.

Manually

If you have not installed MongoDB using a package manager, you can manually download the MongoDB binaries from the MongoDB Download Center.

See 4.4 installation instructions for more information.

Upgrade Process

You can upgrade from MongoDB 4.2 to 4.4 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 replica set one at a time:

  1. Shut down the mongod instance and replace the 4.2 binary with the 4.4 binary.
  2. Restart the 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.

3

Upgrade the primary.

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 4.4 binary.
  2. Restart the member.
4

Enable backwards-incompatible 4.4 features.

At this point, you can run the 4.4 binaries without the 4.4 features that are incompatible with 4.2.

To enable these 4.4 features, set the feature compatibility version (FCV) to 4.4.

Tip

Enabling these backwards-incompatible features can complicate the downgrade process since you must remove any persisted backwards-incompatible features before you downgrade.

It is recommended that after upgrading, you allow your deployment to run without enabling these features for a burn-in period to ensure the likelihood of downgrade is minimal. When you are confident that the likelihood of downgrade is minimal, enable these features.

Tip

Ensure that no initial sync is in progress. Running setFeatureCompatibilityVersion command while an initial sync is in progress will cause the initial sync to restart.

On the primary, run the setFeatureCompatibilityVersion command in the admin database:

copy 
db.adminCommand( { setFeatureCompatibilityVersion: "4.4" } )

Setting featureCompatibilityVersion (fCV) : “4.4” implicitly performs a replSetReconfig to add the term field to the 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 primary as the operation is idempotent.

Additional Upgrade Procedures

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