Amazon ElastiCache is a fully managed in-memory cache service offered by AWS, allowing applications to speed up requests and improve throughput. Key performance metrics include client metrics (e.g., number of connections, Get commands, Set commands), cache performance metrics (e.g., hits, misses, latency), memory metrics (e.g., memory usage, evictions, swap usage), and host-level metrics (e.g., CPU utilization). Monitoring these metrics helps ensure the health and performance of ElastiCache. It is essential to correlate metrics to see the full picture and investigate issues related to events sent by ElastiCache. By monitoring the right metrics, developers can gain insights into their cache's performance and optimize it for better user experience and application responsiveness.