Question 18529 in Amazon Web Sevices Question posted in
The official Amazon Web Services documentation can be found here.

Amazon burstable Instances (e.g. T3) – How much CPU is guaranteed? – Amazon Web Sevices

I have a t3.2xlarge instance in ‘unlimited mode’.

Amazon says this instance type has a "Baseline utilization per vCPU" of 40%: https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-credits-baseline-concepts.html

I sometimes see that my App is slow and CPU is at 60% while CPU idle is at 0% and CPU steal is at 40%.

In my understanding this should not happen. CPU should go beyond 60% in this example (and it sometimes goes beyond 60%).

Does that mean that T3 CPU is not guaranteed up to 100%? Is it only guaranteed up to "Baseline utilization per vCPU" and all burst on top of that is only available if no other VM on the same hardware needs it?

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  1. Chosen as BEST ANSWER
    0

    Amazon support confirmed that if we want to have CPU guaranteed, we need to switch away from a burstable instance. They did not say how much is guaranteed for burstable. So I would say the answer is: "There is no guarantee for any CPU on a burstable instance". They seem to use "baseline utilization" as some kind of soft target, but even that seems not guaranteed.


  2. 0

    It can happen if you don’t have any accrued credits to burn when your application needs to burst above the baseline.

    when credits spent are more than credits earned, the
    instance uses the accrued credits to burst above baseline CPU
    utilization. If there are no accrued credits remaining, then the
    instance gradually comes down to baseline CPU utilization and cannot
    burst above baseline until it accrues more credits.

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