Upgrade a Replica Set to 3.6

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Note

Important

Before you attempt any upgrade, please familiarize yourself with the content of this document.

If you need guidance on upgrading to 3.6, 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 3.6, you must be running a 3.4-series release.

To upgrade from a version earlier than the 3.4-series, you must successively upgrade major releases until you have upgraded to 3.4-series. For example, if you are running a 3.2-series, you must upgrade first to 3.4 before you can upgrade to 3.6.

Preparedness

Before beginning your upgrade, see the Compatibility Changes in MongoDB 3.6 document to ensure that your applications and deployments are compatible with MongoDB 3.6. 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 3.6, if you need to downgrade, we recommend downgrading to the latest patch release of 3.4.

Default Bind to Localhost

Starting in MongoDB 3.6, mongod and mongos instances bind to localhost by default. Remote clients, including other members of the replica set, cannot connect to an instance bound only to localhost. To override and bind to other ip addresses, use the net.bindIp configuration file setting or the --bind_ip command-line option to specify a list of ip addresses.

The upgrade process will require that you specify the net.bindIp setting (or --bind_ip) if your replica set members are run on different hosts or if you wish remote clients to connect to your replica set.

Warning

Before binding to a non-localhost (e.g. publicly accessible) IP address, ensure you have secured your cluster from unauthorized access. For a complete list of security recommendations, see Security Checklist. At minimum, consider enabling authentication and hardening network infrastructure.

For more information, see Localhost Binding Compatibility Changes

Initial Syncs

Before starting the upgrade, ensure that no initial sync is in progress. Performing the upgrade while an initial sync is in progress will cause the initial sync to restart.

Read Concern Majority

Starting in MongoDB 3.6, MongoDB enables support for “majority” read concern by default.

For MongoDB 3.6.1 - 3.6.x, you can disable read concern “majority” to prevent the storage cache pressure from immobilizing a deployment with a primary-secondary-arbiter (PSA) architecture. Disabling “majority” read concern also disables support for change streams

For more information, see Disable Read Concern Majority.

Prerequisites

Download 3.6 Binaries

Via Package Manager

If you installed MongoDB from the MongoDB apt, yum, dnf, or zypper repositories, you should upgrade to 3.6 using your package manager.

Follow the appropriate 3.6 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 3.6 installation instructions for more information.

Upgrade Process

You can upgrade from MongoDB 3.4 to 3.6 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 3.4 binary with the 3.6 binary.
  2. Restart the member.

    Important

    If your replica set members are run on different hosts or if you wish remote clients to connect to your instance, you must specify the net.bindIp setting (or --bind_ip). For more information, see Localhost Binding Compatibility Changes.

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 3.6 binary.
  2. Restart the member.

    Important

    If your replica set members are run on different hosts or if you wish remote clients to connect to your instance, you must specify the net.bindIp setting (or --bind_ip).

4

Enable backwards-incompatible 3.6 features.

At this point, you can run the 3.6 binaries without the 3.6 features that are incompatible with 3.4.

To enable these 3.6 features, set the feature compatibility version (FCV) to 3.6.

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:

db.adminCommand( { setFeatureCompatibilityVersion: "3.6" } )

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