What is an Auto Scaling Group, and what are the scaling policy types?
AWS · Basic level
Answer
An Auto Scaling Group maintains desired EC2 capacity, replaces unhealthy instances, and scales using policies such as target tracking, step scaling, scheduled scaling, and predictive scaling. I prefer metrics that reflect real demand, not only CPU.
Technical explanation
Scaling on request count per target can be better than CPU for web services because it follows user demand more directly.
Compute design should balance availability, scaling speed, startup time, instance limits, health checks, and deployment rollback, not just raw instance size.
Autoscaling and load balancing only work well when health checks reflect readiness and when applications externalize state.
Cost optimization should be tied to utilization data and workload tolerance for interruption, commitment, and architecture changes.
Hands-on example
1. Build a launch template or workload definition with IAM role, security groups, user data/bootstrap, health endpoint, and CloudWatch metrics.
2. Place compute behind an ALB/NLB or scaling group and run a controlled load test to observe scaling and health behavior.
3. Tune scaling policy, warmup/cooldown, target group health checks, and rollback procedure.
4. Compare cost and reliability after the test, then promote the configuration through IaC.
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