Retrieve the target lifecycle state through instance metadata

Each Auto Scaling instance that you launch goes through several lifecycle states. To invoke custom actions from within an instance that act on specific lifecycle state transitions, you must retrieve the target lifecycle state through instance metadata.

For example, you might need a mechanism to detect instance termination from inside the instance to run some code on the instance before it's terminated. You can do this by writing code that polls for the lifecycle state of an instance directly from the instance. You can then add a lifecycle hook to the Auto Scaling group to keep the instance running until your code sends the complete-lifecycle-action command to continue.

The Auto Scaling instance lifecycle has two primary steady states—InService and Terminated—and two side steady states—Detached and Standby. If you use a warm pool, the lifecycle has four additional steady states—Warmed:Hibernated, Warmed:Running, Warmed:Stopped, and Warmed:Terminated.

When an instance prepares to transition to one of the preceding steady states, Amazon EC2 Auto Scaling updates the value of the instance metadata item autoscaling/target-lifecycle-state. To get the target lifecycle state from within the instance, you must use the Instance Metadata Service to retrieve it from the instance metadata.

Local code can access instance metadata from a running instance using one of two methods: Instance Metadata Service Version 1 (IMDSv1) or Instance Metadata Service Version 2 (IMDSv2). IMDSv2 uses session-oriented requests and mitigates several types of vulnerabilities that could be used to try to access the instance metadata. For details about these two methods, see Use IMDSv2 in the Amazon EC2 User Guide for Linux Instances.

The following is example output.

InService

The target lifecycle state is the state that the instance is transitioning to. The current lifecycle state is the state that the instance is in. These can be the same after the lifecycle action is complete and the instance finishes its transition to the target lifecycle state. You cannot retrieve the current lifecycle state of the instance from the instance metadata.

Amazon EC2 Auto Scaling started generating the target lifecycle state on March 10, 2022. If your instance transitions to one of the target lifecycle states after that date, the target lifecycle state item is present in your instance metadata. Otherwise, it is not present, and you receive an HTTP 404 error.

For more information about retrieving instance metadata, see Retrieve instance metadata in the Amazon EC2 User Guide for Linux Instances.

For a tutorial that shows you how to create a lifecycle hook with a custom action in a user data script that uses the target lifecycle state, see Tutorial: Configure user data to retrieve the target lifecycle state through instance metadata.