Ensure connection draining is enabled for AWS ELB

AWS ELB has connection draining disabled which may keep sending requests to de-registering or unhealthy clients.

In AWS Console -

1. Sign in to AWS Console and go to EC2 console.
2. Select one of your load balancers, and click on the Instances tab.
3. Look for Connection Draining and click on Edit to enable it.

In Terraform -

1. In the aws_elb resource, set the connection_draining field to true.

References:
https://docs.aws.amazon.com/elasticloadbalancing/latest/classic/config-conn-drain.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/elb#connection_draining