Amazon ElastiCache for Redis
ElastiCache for Redis User Guide (API Version 2015-02-02)

Upgrading Engine Versions

You can control if and when the protocol-compliant software powering your cache cluster is upgraded to new versions that are supported by ElastiCache. This level of control enables you to maintain compatibility with specific versions, test new versions with your application before deploying in production, and perform version upgrades on your own terms and timelines.

Because version upgrades might involve some compatibility risk, they don't occur automatically. You must initiate them.

You initiate engine version upgrades to your cluster or replication group by modifying it and specifying a new engine version. For more information, see:

Important

  • You can upgrade to a newer engine version, but you can't downgrade to an older engine version. If you want to use an older engine version, you must delete the existing cluster and create it anew with the older engine version.

  • Although engine version management functionality is intended to give you as much control as possible over how patching occurs, ElastiCache reserves the right to patch your cluster on your behalf in the unlikely event of a critical security vulnerability in the system or cache software.

  • ElastiCache for Redis doesn't support switching between Redis (cluster mode disabled) and Redis (cluster mode enabled).

  • The Amazon ElastiCache for Redis engine upgrade process is designed to make a best effort to retain your existing data and requires successful Redis replication.

  • You can't upgrade directly from Redis (cluster mode disabled) to Redis (cluster mode enabled) when you upgrade your engine. The following procedure shows you how to upgrade from Redis (cluster mode disabled) to Redis (cluster mode enabled).

    To upgrade from a Redis (cluster mode disabled) to Redis (cluster mode enabled) engine version

    1. Make a backup of your Redis (cluster mode disabled) cluster or replication group. For more information, see Making Manual Backups.

    2. Use the backup to create and seed a Redis (cluster mode enabled) cluster with one shard (node group). Specify the new engine version and enable cluster mode when creating the cluster or replication group. For more information, see Seeding a New Cluster with an Externally Created Backup.

    3. Delete the old Redis (cluster mode disabled) cluster or replication group. For more information, see Deleting a Cluster or Deleting a Replication Group.

    4. Scale the new Redis (cluster mode enabled) cluster or replication group to the number of shards (node groups) that you need. For more information, see Scaling Redis (cluster mode enabled) Clusters

  • For single Redis clusters and clusters with Multi-AZ disabled, we recommend that sufficient memory be made available to Redis as described in Ensuring You Have Sufficient Memory to Create a Redis Snapshot. In these cases, the primary is unavailable to service requests during the upgrade process.

  • For Redis clusters with Multi-AZ enabled, we also recommend that you schedule engine upgrades during periods of low incoming write traffic. The primary continues to be available to service requests during the upgrade process, except for a few minutes when a failover is initiated.

    Clusters and replication groups with multiple shards are process and patched as follows:

    • All shards are processed in parallel. Only one upgrade operation is performed on a shard at any time.

    • In each shard, all replicas are processed before the primary is processed. If there are fewer replicas in a shard, the primary in that shard may be processed before the replicas in other shards are finished processing.

    • Across all the shards, primary nodes are processed in series. Only one primary node is upgraded at a time.

  • If encryptions is enabled on your current cluster or replication group, you cannot upgrade to an engine version that does not support encryption, such as from 3.2.6 to 3.2.10.

How to Upgrade Engine Versions

You initiate version upgrades to your cluster or replication group by modifying it using the ElastiCache console, the AWS CLI, or the ElastiCache API and specifying a newer engine version. For more information, see the following topics.

Resolving Blocked Redis Engine Upgrades

As shown in the following table, your Redis engine upgrade operation is blocked if you have a pending scale up operation.

Pending Operations Blocked Operations
Scale up Immediate engine upgrade
Engine upgrade Immediate scale up
Scale up and engine upgrade Immediate scale up
Immediate engine upgrade

To resolve a blocked Redis engine upgrade, do one of the following

  • Schedule your Redis engine upgrade operation for the next maintenance window by clearing the Apply immediately check box (CLI use: --no-apply-immediately, API use: ApplyImmediately=false).

     

  • Wait until your next maintenance window (or after) to perform your Redis engine upgrade operation.

     

  • Add the Redis scale up operation to this cluster modification with the Apply Immediately check box chosen (CLI use: --apply-immediately, API use: ApplyImmediately=true). (This effectively cancels the engine upgrade during the next maintenance window by performing it immediately.)