A Health Check is the process of verifying whether a server, application, or service is running correctly and responding to requests. It helps detect unhealthy resources automatically.
With health checks, services like Elastic Load Balancer (ELB) and Auto Scaling regularly monitor Amazon EC2 instances. If an instance becomes unhealthy, traffic is redirected or the instance is automatically replaced.
In simple words, a health check continuously checks if a server or application is healthy and ensures users are connected only to working resources.