What happens if an Auto Scaling instance never becomes healthy?

Core Summary

Auto Scaling terminates and replaces an instance that never passes health checks, which is fine once and expensive in a loop. How long you burn depends on the grace period, the check thresholds, and which health check type the group is actually using. The fix is working out why it's unhealthy: usually startup config, a wrong health endpoint, or a grace period shorter than boot time.