The company’s ecommerce website running on EC2 instances behind an ALB intermittently returns HTTP 500...

Using ALB health checks in the Auto Scaling group will provide more accurate health monitoring and replace instances if they are unhealthy.

ALB Health Checks: Configure health checks based on HTTP response codes, which will detect application-level issues causing the HTTP 500 errors and replace instances as needed.

EC2 vs. ALB Health Checks: EC2 status checks only verify instance hardware and OS, not the application’s responsiveness. By using ALB health checks, Auto Scaling can remove instances that are failing at the application level, thus preventing users from receiving 500 errors.

Replacing the ALB with a Network Load Balancer does not address HTTP 500 errors, and enabling session affinity does not resolve application health issues. The CloudWatch agent would not provide the required health check functionality for automated instance replacement.