Verify the attachment status of your load balancer

After you attach a load balancer, it enters the Adding state while registering the instances in the group. When all instances in the group are registered, it enters the Added state. After at least one registered instance passes the health checks, it enters the InService state. When the load balancer is in the InService state, Amazon EC2 Auto Scaling can terminate and replace any instances that are reported as unhealthy. If no registered instances pass the health checks (for example, due to a misconfigured health check), the load balancer doesn't enter the InService state. Amazon EC2 Auto Scaling doesn't terminate and replace the instances.

When you detach a load balancer, it enters the Removing state while deregistering the instances in the group. The instances remain running after they deregister. By default, connection draining (deregistration delay) is enabled for Application Load Balancers, Network Load Balancers, and Gateway Load Balancers. If connection draining is enabled, Elastic Load Balancing waits for in-flight requests to complete or for the maximum timeout to expire (whichever comes first) before it deregisters the instances.

You can verify the attachment status by using the AWS Command Line Interface (AWS CLI) or AWS SDKs. You cannot verify the attachment status from the console.

To use the AWS CLI to verify the attachment status

The following describe-traffic-sources command returns the attachment status of all traffic sources for the specified Auto Scaling group.

aws autoscaling describe-traffic-sources --auto-scaling-group-name my-asg

The example returns the ARN of the Elastic Load Balancing target group that's attached to the Auto Scaling group, along with the attachment status of the target group in the State element.

{
    "TrafficSources": [
        {
            "Identifier": "arn:aws:elasticloadbalancing:region:account-id:targetgroup/my-targets/1234567890123456",
            "State": "InService",
            "Type": "elbv2"
        }
    ]
}