Ref: https://learn.cantrill.io/courses/1820301/lectures/41301445

• Summary:
• Contents:

EC2 ASG - Lifecycle Hooks

Diagram: https://github.com/acantril/aws-sa-associate-saac03/blob/main/1500-HA_and_SCALING/00_LEARNINGAIDS/ASG-LifecycleHooks-1.png

• Normal EC2 instance launch/termination behavior in ASGs:
  • Launch: instance moves to Pending state and then to InService state
  • Termination: instance moves to Terminating state and then to Terminated state
  • ❗ Without ASG lifecycle hooks, processes automatically carried out by the ASG, and NOTHING can be done during those transitions
• 🔧 ASG lifecycle hooks allow taking custom actions on instances during ASG actions
  • …i.e. instance launch/termination transitions
• ❗ With lifecycle hooks in place, instances are PAUSED within the launch/termination flow
  • Flow resumes when one of these 2 happen:
    1. A (configurable) timeout expires → then either continue or abandon the ASG action
       • Default timeout is 3600s (one hour)
    2. CompleteLifecycleAction operation is executed
       • Execute once you have performed whatever activity you wanted to perform
       • Alternatively, execute complete-lifecycle-action command (e.g. in AWS CLI)
• Examples of custom actions to take:
  • Load/index data before bringing a new instance to service
  • Backup data or logs, or tidy up an instance before terminating it
• Can be integrated with Amazon EventBridge & SNS Notifications
  • Allows for event-driven processing based on launch/termination of ASG instances