Health Checks in Express Mode

ALB Target Group Health Checks

Express Mode Express Gateway Service
The aws_ecs_express_gateway_service Terraform resource that provisions an ECS service with managed ALB, auto scaling, and simplified configuration for HTTP/HTTPS web applications and APIs. relies on ALB target group health checks to determine whether tasks are healthy and ready to receive traffic. When you define a health_check_path in your Express Gateway Service resource, the shared ALB Shared ALB
The Application Load Balancer shared by up to 25 Express services in the same VPC using Host header routing rules. periodically sends HTTP requests to that path on each registered target. If the target responds with an HTTP 200 status code, it is considered healthy.

main.tf

resource "aws_ecs_express_gateway_service" "this" {
  # ...

  primary_container {
    # ...
    health_check_path = "/health"
  }
}

The ALB checks each target at a regular interval (typically every 30 seconds). A target must return a successful response within the configured timeout to be marked healthy. If a target fails consecutive health checks, the ALB stops routing traffic to it and Express Mode takes corrective action.

How Health Checks Drive Deployments

During a deployment, Express Mode starts new tasks and registers them with the target group. The ALB health checks determine whether the new tasks are serving traffic correctly. If new tasks pass health checks, the deployment proceeds and old tasks are drained. If new tasks fail health checks, the RollbackAlarm RollbackAlarm
A CloudWatch metric alarm created by Express Mode that triggers automatic deployment rollback when new tasks fail ALB health checks. fires and Express Mode automatically rolls back to the previous healthy deployment.

This makes health_check_path a critical configuration. The path must point to an endpoint in your application that:

Requirement	Description
Returns HTTP 200	The endpoint must respond with a 200 status code when the application is ready to serve traffic
Responds quickly	The response must complete within the health check timeout (default 5 seconds)
Validates readiness	The check should confirm the application is fully initialized and can handle requests
No authentication	The health check path must be accessible without auth headers since the ALB sends plain requests

No Container healthCheck Support

Caution

Express Mode does not support the ECS container-level healthCheck configuration. The Express Gateway Service API does not accept a healthCheck block in the task definition. All health monitoring is performed exclusively through ALB target group health checks via health_check_path.

In classic ECS, you can define a healthCheck command in the container definition (for example, curl localhost:8080/health) that the ECS agent runs inside the container. Express Mode omits this capability entirely. As a result, the ECS Tasks tab in the console displays Health status: Unknown for Express Mode tasks — this is expected and does not indicate a problem.

Operational health for Express Mode services is determined solely by the ALB target group status. If targets are registered and passing ALB health checks, the service is healthy regardless of what the ECS Tasks tab shows.

Implications for Debugging

Because Express Mode uses only ALB-level health checks, your debugging workflow differs from classic ECS:

Scenario	Where to check
Tasks healthy and serving traffic	EC2 → Target Groups → Targets tab shows healthy
Tasks unhealthy or failing	EC2 → Target Groups → Targets tab shows unhealthy with a reason code
Health status Unknown in ECS	Normal for Express Mode — check ALB target group instead
Deployment rolling back	New tasks failed ALB health checks — inspect target group health reason and CloudWatch Logs

Tip

Always check EC2 → Target Groups → Targets for the definitive health status of your Express Mode service. The ECS Tasks tab health column is not applicable.