AWS SysOps Exam Key Points: Auto Scaling Groups (ASG) and Launch Configurations

Lifecycle Hooks

• Lifecycle hooks allow custom actions to be executed during ASG instance initiation and termination.
• Default behavior: Instances go from pending to in-service immediately.
• With lifecycle hooks:
  • Pending Lifecycle: The Instance enters a pending wait state for initial setup scripts, then proceeds to move to in-service.
  • Termination Lifecycle: The instance enters the terminating wait state for actions like log retrieval or AMI creation, andthen terminating proceeds to move to termination.

• Use-cases: Cleanup, log extraction, and health checks before instances start or are terminated.
• Integration with other AWS services: EventBridge, SNS, SQS for triggering actions based on lifecycle events.

Launch Configurations vs. Launch Templates

• Both specify parameters for launching EC2 instances (AMI, instance type, key pair, security groups, etc.).
• Launch Configurations:
  • It cannot be edited; it must be recreated for changes.
  • Considered legacy and not recommended for new implementations.
• Launch Templates:
  • Support multiple versions and editing.
  • Allow configuration reuse and inheritance.
  • It can provision on-demand and spot instances or a mix.
  • Support advanced features like placement groups, capacity reservations, dedicated hosts, and T2 unlimited burst.
  • It was recommended by AWS for new implementations.

Auto Scaling with SQS

• Scale ASG based on SQS queue length using CloudWatch metrics and alarms.
• CloudWatch metric: ApproximateNumberOfMessagesVisible.
• Alarm triggers scaling policy based on queue length.

Health Checks

• Ensure high availability with multi-AZ ASG and at least two instances.