ElastiCache

Amazon ElastiCache is a web service that makes it easy to deploy, operate and scale an in-memory cache in the cloud. The service improves the performance of web applications by allowing you to retrieve information from fast, managed, in-memory caches, instead of relying entirely on slower disk-based databases.

ElastiCache supports two open-source in-memory caching engines:

• Memcached

• Redis

Monitoring

When it comes to monitoring caching engines, there are 4 important metrics to look at:

• CPU utilization

• Swap usage

• Evictions

• Concurrent connections

CPU utilizations

• Memcached

  • Multi-threaded

  • Can handle loads up to 90%. If it exceeds 90%, add more nodes to the cluster

• Redis

  • Not multi-threaded. To determine the point in which to scale, take 90% and divide by the number of cores.

Swap usage

• Memcached

  • Should be around 0 most of the time and should not exceed 50 Mb.

  • If this exceeds 50 Mb, you should increase the memcached_connections_parameter

• Redis

  • No swap usage metrics, instead use reserved_memory

Evictions

• Memcached

  • There is no recommended setting. Choose a threshold based off your application. Either scale up (increase the memory of the existing nodes) or scale out (add more nodes).

• Redis

  • There is no recommended setting, choose a threshold based off your application

  • Only scale out (add read replicas)

Concurrent connections

• Memcached and Redis

  • There is no recommended setting

  • If there is a spike in number of concurrent connections, this can either mean a large traffic spike or your application is not releasing connections as it should be.