EC2 Auto Scaling lifecycle hooks are basically hooks into the launch and termination process of EC2 instances in an Auto Scaling group. They give you a chance to run custom actions when an instance is starting up or shutting down.
Think of it like a “pause button” at key points in the lifecycle of an instance.
How lifecycle hooks work
When Auto Scaling launches or terminates an instance, lifecycle hooks let you:
- Pause the process so you can run a custom task before proceeding.
- Run scripts or send data (e.g., to an auditing system).
- Ensure proper configuration before an instance becomes fully operational (or before it is destroyed).
Two main lifecycle states
- Pending:Wait
- Triggered when an instance is launched.
- The instance goes into a waiting state until the lifecycle hook action completes.
- Example: Run a script that sends auditing info before the instance is marked “InService”.
- Terminating:Wait
- Triggered when an instance is terminated.
- The instance stays in a waiting state so your action can complete.
- Example: Send final audit logs before the instance is removed.
Why this is powerful
- Automated → works with Auto Scaling without manual intervention.
- Precise timing → runs exactly at instance launch or termination.
- Scalable → works no matter how many instances Auto Scaling launches/terminates.
- Customizable → you can send data to an audit system, run configuration scripts, or notify other systems.
Example use case for your question
For your auditing system:
- Lifecycle hook at launch → run a script that sends OS version, patching info, and installed software to the audit system.
- Lifecycle hook at termination → run a final script sending termination logs.
That way, all instances always send audit info immediately on launch and termination without needing scheduled tasks or manual scripting.
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