ALB Health Check

Your Application Load Balancer periodically sends requests to its registered targets to test their status. These tests are called health checks.

Each load balancer node routes requests only to the healthy targets in the enabled Availability Zones for the load balancer. Each load balancer node checks the health of each target, using the health check settings for the target groups with which the target is registered. After your target is registered, it must pass one health check to be considered healthy. After each health check is completed, the load balancer node closes the connection that was established for the health check.

The load balancer sends a health check request to each registered target every HealthCheckIntervalSeconds seconds, using the specified port, protocol, and ping path. Each health check request is independent and the result lasts for the entire interval.

Reference : https://docs.aws.amazon.com/elasticloadbalancing/latest/application/target-group-health-checks.html