AWS EC2 - Do auto scaled instances run for a minumum amount of time (CPU load average based)

I've been running a scheduler for my work load for awhile now. Recently demand has become more inconsistent, and the workload has been backing up at what should be slow points of the week. I've started implementing auto scale groups in two of my regions that scale based on CPU load.

I've got it set at 80% CPU load average, and my queued work is good at maximizing the CPU, and I opted for more, smaller instances that are cheaper to run. Everything appears to be operating ideally, but I just have a concern about instances being started and stopped too often. I know on EC2 you pay for the full hour regardless of how long it runs during that hour, so...

Is the auto scaling taking this into account and leaving them running for at least a certain amount of time like ~30-45 minutes?

Do I have to instead work with the CPU average and the various timeouts to help prevent wasteful start/stops?

1 answer

  • answered 2018-10-15 20:48 spg

    Depending on which AMI you're running, you might benefit from per-second billing. In this case, you'll only be charged a minimum of 60 seconds. From my understanding of your use case, this billing method would be ideal (cost-wise) for you, as you seem to frequently start and stop instances that live for short amounts of time.

    To my knowledge, there's no built-in mechanism in autoscaling that will try to optimize your EC2 usage to minimise costs.

    If, however, you're using an AMI that is not eligible for per-second billing, you could look into Spot instances to further minimse your costs, if your workload applies to this scheduling model.