Amazon Elastic Load Balancer (ELB) is a widely used AWS service that ensures a smooth user experience and provides fault tolerance for web and mobile applications. It continuously checks for unhealthy EC2 instances and reroutes traffic to healthy ones. Key ELB performance metrics include load balancer metrics, such as RequestCount, SurgeQueueLength, and SpilloverCount, which measure the number of requests, queued requests, and dropped requests, respectively. These metrics are crucial to ensure the load balancer itself and EC2 instances behind it remain healthy. Additionally, backend-related metrics like HealthyHostCount, UnHealthyHostCount, Latency, and BackendConnectionErrors provide insights into the health and performance of backend instances. Monitoring these metrics is essential for identifying potential issues, such as high latency, overloaded backend hosts, or network issues, and taking corrective actions to ensure a smooth user experience. By understanding and monitoring these key ELB performance metrics, users can gain valuable insights into their load balancers' performance and backend servers' health, ultimately leading to improved application scalability and reliability.