My instances re-appears again even after getting terminated

This issue could be related to Auto Scaling groups. When instances are part of an Auto Scaling group, terminating an instance manually will often result in the Auto Scaling group automatically launching a new replacement instance to maintain the desired capacity.

Here are some potential causes and solutions:

1. Auto Scaling Group Behavior: If your instances are part of an Auto Scaling group, the group will automatically launch new instances when existing ones are terminated to maintain the desired capacity. This is expected behavior.

2. Check Auto Scaling Activity Logs: Review your Auto Scaling activity logs to see if there are termination logs followed by instance launch logs. In some cases, you might only see termination logs if multiple instances are running in the group.

3. To Properly Terminate Instances:

• If you want to permanently remove instances, you should update or delete the Auto Scaling group rather than just terminating the instances.
• Reduce the desired capacity of your Auto Scaling group to zero, or delete the Auto Scaling group entirely.
• Make sure to also delete associated resources like launch templates or launch configurations.

4. Verify All Regions: Double-check that you're looking in the correct AWS region, as instances might appear to be terminated in one region but could be running in another.

5. Check for Hidden Resources: Use AWS tools to find any hidden resources that might be causing instances to reappear.

If you've verified all these steps and the instances still reappear after termination, it would be advisable to open a support case with AWS for further assistance.
Sources
EC2 Auto-Scaling Instances Retaining Old Data After Termination | AWS re:Post
EC2 instance terminated after reboot | AWS re:Post

Instance IDs are unique: AWS never reuses an instance ID for a new launch. Looks like your instance is not truly terminated: The instances were likely only stopped and then restarted by another service. Check Auto Scaling Group, Spot Fleet, or another AWS service (like Elastic Beanstalk, EKS, CloudFormation) is configured to maintain a "desired state" that includes these specific instances.

Since you mention specific instance id and you cannot terminate them, there could be 2 reasons I can think of.

• You don't have permissions to terminate the EC2.
• The EC2s have termination protection enabled. Disable it and retry.