Upgrading the engine version of a Multi-AZ DB cluster for Amazon RDS
Amazon RDS provides newer versions of each supported database engine so that you can keep your Multi-AZ DB cluster up to date. This topic explains the process of upgrading a Multi-AZ DB cluster to newer versions.
Upgrading a Multi-AZ DB cluster involves selecting a new compatible engine version and planning for potential downtime. The process ensures minimal disruption by utilizing the failover capabilities of the Multi-AZ architecture. During the upgrade, the primary instance is updated first, followed by a failover to the standby instance to maintain availability. Best practices include performing upgrades during low-traffic periods, testing in non-production environments, and verifying application compatibility with the new version.
Topics
Minor version upgrades
A minor version upgrade includes only changes that are backward-compatible with existing applications. When you initiate a minor version upgrade, Amazon RDS first upgrades the reader DB instances one at a time. Then, one of the reader DB instances switches to be the new writer DB instance. Amazon RDS then upgrades the old writer instance (which is now a reader instance).
Downtime during the upgrade is limited to the time it takes for one of the reader DB instances to become the new writer DB instance. This downtime acts like an automatic failover. For more information, see Failing over a Multi-AZ DB cluster for Amazon RDS. Note that the replica lag of your Multi-AZ DB cluster might affect the downtime. For more information, see Replica lag and Multi-AZ DB clusters.
For RDS for PostgreSQL Multi-AZ DB cluster read replicas, Amazon RDS upgrades the cluster member instances one at a time. The reader and writer cluster roles don't switch during the upgrade. Therefore, your DB cluster might experience downtime while Amazon RDS upgrades the cluster writer instance.
Note
The downtime for a Multi-AZ DB cluster minor version upgrade is typically 35 seconds. When used
with RDS Proxy, you can further reduce downtime to one second or less. For more
information, see Using Amazon RDS Proxy. Alternately, you can use an open
source database proxy such as ProxySQL
Major version upgrades
A major version upgrade can introduce changes that aren't compatible with existing applications.
When you initiate a major version upgrade of an RDS for PostgreSQL Multi-AZ DB cluster, Amazon RDS simultaneously upgrades the reader and writer instances. Therefore, your DB cluster might not be available until the upgrade completes.
When you initiate a major version upgrade of an RDS for MySQL Multi-AZ DB cluster, Amazon RDS upgrades the cluster member instances one at a time, so replication occurs from a lower engine version to a higher one. It's important to ensure that your workload is compatible with both the source and target engine versions during a major version upgrade, as engine versions might differ in syntax and features.
Note
Like minor version upgrades, the downtime for an RDS for MySQL major version upgrade is typically 35 seconds. When used with RDS Proxy, you can further reduce downtime to one second or less. For more information, see Using Amazon RDS Proxy.
Upgrading a Multi-AZ DB cluster
The process for upgrading the engine version of a Multi-AZ DB cluster is the same as the process for
upgrading a DB instance engine version. For instructions, see Upgrading
a DB instance engine version. The only difference is that when using
the AWS Command Line Interface (AWS CLI), you use the modify-db-cluster command and specify the
--db-cluster-identifier parameter (along with the
--allow-major-version-upgrade parameter).
For more information about major and minor version upgrades, see the following documentation for your DB engine:
Upgrading Multi-AZ DB cluster read replicas
Amazon RDS doesn't automatically upgrade Multi-AZ DB cluster read replicas. For minor version upgrades, you must first manually upgrade all read replicas and then upgrade the cluster. Otherwise, the upgrade is blocked. When you perform a major version upgrade of a cluster, the replication state of all read replicas changes to terminated. You must delete and recreate the read replicas after the upgrade completes. For more information, see Monitoring read replication.
