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

Monitoring ElastiCache Events

When significant events happen on a cluster, such as a failure to add a node, success in adding a node, the modification of a security group and others, ElastiCache sends notification to a specific Amazon SNS topic. 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.