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If your ECS Managed Instances get stuck in the DRAINING state because they lost connection to the agent, you can manually force deregister these instances to move forward with deleting the capacity provider. This often happens when there’s a network problem, like if a NAT instance gets terminated before the instances can finish draining properly.
The problem usually occurs because the ECS agent can’t communicate with the ECS service. Even if you fix the network issues later—such as restoring the NAT instance—the agent might not automatically reconnect because it needs proper outbound connectivity to the ECS endpoints.
To fix this, use the AWS Command Line Interface (CLI) to forcibly deregister the problematic container instance. Here’s the command you need:
aws ecs deregister-container-instance –cluster your-cluster-arn –container-instance your-container-instance-arn –force
Replace “your-cluster-arn” with your cluster’s Amazon Resource Name, and “your-container-instance-arn” with the ARN of the instance you want to deregister. The “–force” flag is essential here because it allows deregistration even if the agent is disconnected.
Looking ahead, it’s a good idea to enable managed draining on your capacity provider. This will ensure that tasks are drained smoothly when instances need to be terminated, reducing the chances of manual intervention:
aws ecs update-capacity-provider –name your-capacity-provider-name –auto-scaling-group-provider ‘{“managedDraining”: “ENABLED”}’
Also, consider adding redundancy to your network setup, like multiple NAT gateways, to avoid losing connectivity in the future.
Understanding and implementing these steps can save a lot of time and prevent interruptions when managing your ECS instances.
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