# Lifecycle Hooks
* Lifecycle hooks **enable you to perform custom actions by pausing instances as an Auto Scaling group launches or terminates them**.
* **When an instance is paused, it remains in a wait state either until you complete the lifecycle action** using the complete-lifecycle-action command or the `CompleteLifecycleAction` operation, or until the timeout period ends (one hour by default).
* For example, your **newly launched instance completes its startup sequence and a lifecycle hook pauses the instance**.
* **While the instance is in a wait state, you can install or configure software on it**, making sure that your instance is fully ready before it starts receiving traffic.
* For another example of the use of lifecycle hooks, **when a scale-in event occurs, the terminating instance is first deregistered from the load balancer** (if the Auto Scaling group is being used with Elastic Load Balancing).
* Then, a **lifecycle hook pauses the instance before it is terminated**.
* **While the instance is in the wait state, you can, for example, connect to the instance and download logs or other data before the instance is fully terminated**.
* This shows the transitions between instance states in this process:
