amazon-ebs builder force_deregister flag: handling AMIs attached to running instances

Goal

To understand how Packer’s force_deregister option behaves when an AMI with the target name is currently attached to a running EC2 instance.

Constraints

The build configuration is identical across local CI and production environments, but the outcome differs. The AWS region, IAM permissions for ec2:DeregisterImage, and the state propagation of image deregistration may influence the result. The ambiguity in the official documentation leads to inconsistent image management and potential outages in production.

Unresolved Questions

• What is the exact sequence of actions Packer takes when force_deregister is true and the target AMI is attached to a running instance?
• How do region‑specific IAM policies or image state propagation delays affect the success or failure of the deregistration step?
• Should CI pipelines incorporate pre‑emptive instance termination or a conditional check before invoking force_deregister to avoid silent failures?