You can deregister your container once you finish with it. Once you deregister it, then you are no longer able to accept the tasks. Running tasks under deregistered container will remain running or stopping. So this task becomes orphaned and no longer monitored by Amazon ECS.
If it might be possible that an orphaned task is still part of the Amazon ECS service, then the service scheduler will start another copy of the same task on a different instance. Orphaned tasks that are registered with the Application Load Balancer or Classic Load Balancer target group are deregistered.
After deregistering the container instance, it will remove the instance from the cluster but it will not terminate the EC2 instance. ...
