CODEWITHSUNDEEP
amazon-web-servicesredisamazon-elasticache
Chris
Chris

Reputation: 6085

Can you dynamically resize an ElastiCache cluster with (cluster mode enabled)?

According to this doc:

Currently, however, unlike Redis (cluster mode disabled) clusters, once a Redis (cluster mode enabled) cluster is created, its structure cannot be altered in any way; you cannot add or delete nodes or shards. If you need to add or delete nodes, or change node types, you must create the cluster anew. (source)

However, this doc seemingly describes a process to add shards to your cluster:

By using online resharding and shard rebalancing with Amazon ElastiCache for Redis version 3.2.10, you can scale your ElastiCache for Redis (cluster mode enabled) dynamically with no downtime. This approach means that your cluster can continue to serve requests even while scaling or rebalancing is in process. (source)

I'm presumably missing something since I've been staring at this for so long, but what is it?

Upvotes: 1

Views: 3838

Answers (1)

Chris
Chris

Reputation: 6085

ElastiCache docs are way out of date; new announcements change what's available even when the three-year old docs remain unchanged. Redis on ElastiCache introduced support for online resizing in 2017. From the announcement:

You can now adjust the number of shards in a running ElastiCache for Redis cluster while the cluster remains online and responding to requests. This gives you the power to respond to changes in traffic and data volume without having to take the cluster offline or to start with an empty cache. You can also rebalance a running cluster to uniformly redistribute slot space without changing the number of shards.

I wish they'd update their 2015 (!) docs, but at any rate, this is the latest we have on the subject. As of October 19, 2018, on a cluster with cluster mode enabled:

You can:

  • Scale out (add shards)
  • Scale in (remove shards)
  • Rebalance (move keys among shards)
  • Online resharding and shard balancing

You cannot:

  • Scale up/down (change node type)
  • Upgrade your engine
  • Configure shards independently

Source: https://docs.aws.amazon.com/AmazonElastiCache/latest/red-ug/redis-cluster-resharding-online.html

Upvotes: 4

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