Is it possible to have a Cloudwatch alarm of the 'free memory' of a ElastiCache Redis cluster?

Question

I'm looking to set up a cloudwatch alarm on a Redis cluster in ElastiCache rather than each individual node.

Is this possible in cloudwatch? so far I've only found ways to set alarms on each individual node, however that isn't very scalable if in the event we add/remove nodes.

TIA

Answer 1

The straight-forward solution, i.e. a CloudWatch metric FreeableMemory aggregated over a single Redis cluster does not exist. It follows, that there is no simple CloudWatch alarm you can establish to do that.

However, there are some workarounds:

• You can create a lambda function, that retrieves the FreeableMemorymetric for all nodes, and pushes a new aggregated metric. This is actually very doable and reliable. You could possibly use CloudWatch math expressions for that, too.
• You can use the metric Aggregated across Clusters > FreeableMemory which does seem to aggregate over all existing clusters - however, this will cease working as soon as you start a second ElastiCache cluster.
• Sadly, you can not use CloudWatch math expressions in CloudWatch alarms. However, as far as I know it is a feature currently in development. In any case, it would probably help to contact AWS Support to add your voice to the feature request.