What’s the difference between AWS ASG Cooldown Period and health check grace period?


AWS Autoscaling has 2 concepts:

  • Cooldown period: From AWS documentation: the cooldown period helps to ensure that your Auto Scaling group doesn’t launch or terminate additional instances before the previous scaling activity takes effect. You can configure the length of time based on your instance warmup period or other application needs. Details are here.
  • Health check grace period: From AWS documentation: frequently, an Auto Scaling instance that has just come into service needs to warm up before it can pass the health check. Amazon EC2 Auto Scaling waits until the health check grace period ends before checking the health status of the instance. Details are here.

But I can’t figure out the difference between them. Can somebody help?

Thanks in advance.


A few differences to consider:

The cooldown period is scoped to an auto-scaling action; if that action launches 3 instances, the cooldown period starts when the last instance is ready. Health check grace periods are scoped to an individual instance.

Auto-scaling cooldowns can be applied to many different auto-scaling policies, such as policies for when things scale in. You can delay the termination of additional instances for a set period time. Health check grace periods are only for scaling out.

Cooldowns will be ignored if a health check fails and causes another auto-scaling event. Grace periods will always be in place for the defined amount of time.

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