ASG Policy Types and Lifecycle Hooks
Explore scaling policy types and lifecycle hooks in AWS Auto Scaling Groups to control instance behavior during scaling events. Learn how to apply simple, step, and target tracking policies, and implement lifecycle hooks for custom initialization and graceful termination. Understand these key concepts to manage scalable, resilient applications and prepare for the AWS Certified Developer – Associate exam.
For developers preparing for the AWS Certified Developer – Associate (DVA-C02) exam, understanding how to control Auto Scaling group (ASG) behavior is crucial. This lesson focuses on two key aspects of ASG functionality: scaling policies and life cycle hooks. These tools allow us to efficiently scale applications based on real-time metrics and enable fine-grained control over instance behavior during launch and termination. We’ll explore how to select the right policy type for different workload patterns and implement lifecycle hooks for custom initialization or graceful shutdowns—highly testable areas in the exam’s “Development” and “Deployment” domains.
Scaling policies
ASGs’ scaling policies are the brains of the group. They determine when and how the group should adjust the number of EC2 instances. Each policy type evaluates metrics and defines actions like launching or terminating instances.
Let’s explore each to understand how they behave in real-world scenarios.
Simple scaling policies
Simple scaling policies are event-driven. A single CloudWatch alarm can trigger a single scaling activity. For example, if average CPU utilization exceeds 70%, the policy adds two EC2 instances. After the action, a cooldown period ensures stability before the next scaling event. This approach is easy to implement but may not be responsive enough for rapidly changing traffic.
Consider a blog site experiencing periodic traffic spikes precisely at noon. A simple scaling policy might add ...