Upgrade a Standalone to 4.2
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The following steps outline the procedure to upgrade a standalone
mongod from version 4.0 to 4.2.
Important
Before you attempt any upgrade, please familiarize yourself with the content of this document.
If you need guidance on upgrading to 4.2, MongoDB professional services offer major version upgrade support 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 4.2, you must be running a 4.0-series release.
To upgrade from a version earlier than the 4.0-series, you must successively upgrade major releases until you have upgraded to 4.0-series. For example, if you are running a 3.6-series, you must upgrade first to 4.0 before you can upgrade to 4.2.
Check Driver Compatibility
Before you upgrade MongoDB, check that you're using a MongoDB 4.2-compatible driver. Consult the driver documentation for your specific driver to verify compatibility with MongoDB 4.2.
Upgraded deployments that run on incompatible drivers might encounter unexpected or undefined behavior.
Preparedness
Before beginning your upgrade, see the Compatibility Changes in MongoDB 4.2 document to ensure that your applications and deployments are compatible with MongoDB 4.2. 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
Starting in MongoDB 7.0, you cannot downgrade your deployment's binary version without assistance from support.
To learn more, see Downgrade 7.0 to 6.0.
Prerequisites
MMAPv1 to WiredTiger Storage Engine
MongoDB 4.2 removes support for the deprecated MMAPv1 storage engine.
If your 4.0 deployment uses MMAPv1, you must change the 4.0 deployment to WiredTiger Storage Engine before upgrading to MongoDB 4.2. For details, see Change Standalone to WiredTiger.
Increase Open Files ulimit Setting
Starting in MongoDB 4.2, incoming connections to a mongod or
mongos instance require two file descriptors. In previous
versions of MongoDB, incoming connections required one file
descriptor.
Prior to upgrading from MongoDB 4.0 to 4.2, you may need to increase the
value of your open files ulimit setting (-n).
Review Current Configuration
With MongoDB 4.2, the mongod and
mongos processes will not start with
MMAPv1 Specific Configuration Options. Previous versions of MongoDB running
WiredTiger ignored MMAPv1 configurations options if they were specified.
With MongoDB 4.2, you must remove these from your configuration.
Feature Compatibility Version
The 4.0 instance must have featureCompatibilityVersion set
to 4.0. To check featureCompatibilityVersion:
db.adminCommand( { getParameter: 1, featureCompatibilityVersion: 1 } )
The operation should return a result that includes
"featureCompatibilityVersion" : { "version" : "4.0" }.
To set or update featureCompatibilityVersion, run the following
command:
db.adminCommand( { setFeatureCompatibilityVersion: "4.0" } )
For more information, see setFeatureCompatibilityVersion.
Download 4.2 Binaries
Via Package Manager
If you installed MongoDB from the MongoDB apt, yum, dnf, or
zypper repositories, you should upgrade to 4.2 using your package
manager.
Follow the appropriate 4.2 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 4.2 installation instructions for more information.
Upgrade Process
Enable backwards-incompatible 4.2 features.
At this point, you can run the 4.2 binaries without the 4.2 features that are incompatible with 4.0.
To enable these 4.2 features, set the feature compatibility
version (fCV) to 4.2.
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.
Run the setFeatureCompatibilityVersion command against the admin database:
db.adminCommand( { setFeatureCompatibilityVersion: "4.2" } )
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 as the operation is idempotent.
Post Upgrade
TLSOptions Replace DeprecatedSSLOptions- Starting in MongoDB 4.2, MongoDB deprecates the SSL options for the
mongod, the mongos, and the
mongoshell as well as the correspondingnet.sslOptions configuration file options.To avoid deprecation messages, use the newTLSoptions for the mongod, the mongos, and themongo.For the command-line TLS options, refer to the mongod, mongos, and
mongoshell pages.For the corresponding
mongodandmongosconfiguration file options, refer to the configuration file page.For the connection string
tlsoptions, refer to the connection string page.
- 4.2+ compatible Drivers Retry Writes by Default
- Drivers compatible with MongoDB 4.2 and higher enable
Retryable Writes by default. Earlier drivers require the
retryWrites=trueoption. TheretryWrites=trueoption can be omitted in applications that use drivers compatible with MongoDB 4.2 and higher.To disable retryable writes, applications that use drivers compatible with MongoDB 4.2 and higher must includeretryWrites=falsein the connection string.
Additional Upgrade Procedures
To upgrade a replica set, see Upgrade a Replica Set to 4.2.
To upgrade a sharded cluster, see Upgrade a Sharded Cluster to 4.2.