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

Monitoring ElastiCache Events

When significant events happen for a cluster, ElastiCache sends notification to a specific Amazon SNS topic. Examples include a failure to add a node, success in adding a node, the modification of a security group, and others. By monitoring for key events, you can know the current state of your clusters and, depending upon the event, be able to take corrective action.