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Amazon ElastiCache
ElastiCache for Memcached 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.

To upgrade to a newer Memcached version, modify your cache cluster specifying the new engine version you want to use. Upgrading to a newer Memcached version is a destructive process – you lose your data and start with a cold cache. For more information, see Modifying an ElastiCache Cluster.

You should be aware of the following requirements when upgrading from an older version of Memcached to Memcached version 1.4.33 or newer. CreateCacheCluster and ModifyCacheCluster fails under the following conditions:

  • If slab_chunk_max > max_item_size.

  • If max_item_size modulo slab_chunk_max != 0.

  • If max_item_size > ((max_cache_memory - memcached_connections_overhead) / 4).

    The value (max_cache_memory - memcached_connections_overhead) is the node's memory useable for data. For more information, see Memcached Connection Overhead.

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.

  • Because the Memcached engine does not support persistence, Memcached engine version upgrades are always a disruptive process which clears all cache data in the cluster.

How to Upgrade Engine Versions

You initiate version upgrades to your cluster 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.