What happens if an Auto Scaling instance never becomes healthy?

Core Summary

An unhealthy instance in Auto Scaling will be eventually terminated and replaced, but how long you wait depends on your health check configuration and cooldown settings. If the instance is stuck unhealthy, it consumes resources and may keep getting replaced in a loop. The fix is: diagnose why it is unhealthy, fix the root cause (usually startup configuration or resource limits), or increase the health check timeout if it is just slow to boot.