Packer Amazon EBS Builder and AWS API: shutdown_stop vs shutdown_terminate behavior

Answer first

Packer amazon-ebs does not snapshot after shutdown. The AMI is created first, then the builder instance is shut down. shutdown_behavior controls only the final EC2 API call that Packer makes after the image is ready.

• shutdown_behavior = "stop": Packer issues StopInstances after the guest OS shutdown sequence. The instance moves to stopped, the instance ID and attached EBS volumes persist, and you can start it later for inspection.
• shutdown_behavior = "terminate": Packer issues TerminateInstances after the image is ready. The instance moves to terminated and is unrecoverable. EBS volumes are removed according to each volume's delete_on_termination setting.

Packer waits for the AMI to reach available before it proceeds to the shutdown step. Termination is not issued until image creation is confirmed complete.

Confirmed facts

• The amazon-ebs builder supports shutdown_behavior with values terminate default and stop. This setting determines the final EC2 API call performed after AMI creation.
• With terminate, Packer calls TerminateInstances. The instance is terminated and EBS volumes are removed per their delete_on_termination flag.
• With stop, Packer calls StopInstances after OS shutdown. The instance remains stopped with volumes attached and can be started later.
• Instance store volumes are lost on both stop and terminate. Stopped instances continue to incur EBS storage charges; terminate is required for full cost removal.

Likely explanation, not confirmed from docs in this brief

The clean filesystem sync depends on the guest OS shutdown, not on the EC2 stop/terminate call itself.

• shutdown_command runs inside the guest OS before Packer invokes the EC2 StopInstances or TerminateInstances API. A graceful sync therefore depends on the OS completing shutdown and the communicator timeout settings.
• shutdown_stop does not guarantee a clean filesystem sync before the AMI snapshot is triggered because the snapshot is triggered by CreateImage while the instance is still running, before any shutdown.
• stop is commonly used for debugging or reusing the builder host to inspect build artifacts without relaunch. terminate is the default for clean up and cost avoidance.

Steps needed for this case

1. Inspect the amazon-ebs source block for shutdown_behavior. Example:

   source "amazon-ebs" "example" {
     shutdown_behavior = "stop"  # or "terminate"
     shutdown_command  = "..."
   }

2. After a build, check EC2 console for the builder instance state and CloudTrail for StopInstances or TerminateInstances events for that instance ID.
3. Check EBS volume attachment and delete_on_termination flag to confirm persistence expectations for stop vs terminate.

To give a precise recommendation for your environment, what Packer version and shutdown_behavior value are you using, and do you have a shutdown_command configured? That changes whether a graceful OS sync is attempted before the final API call.