EC2 CPU credit balance stuck at zero even not spending any credit for few hours
Hi, I have been using an t3.micro instance (unlimited mode) for years, few months ago I have significantly added workload to it and it works perfectly fine.
Until recently I found my bill has an entry "Amazon Elastic Compute Cloud T3CPUCredits" then I realized that my reserved instance is running out of CPU credits. So I tried to remove the extra workload and the CPU utilization fall back below 1% and CPU credit usage keep below 0.09 all the time. 6 Hours passed, surprisingly the CPU credit balance still being zero.
Could anyone help suggest what is going on and how to fix it please?
Thank you so much.
- Newest
- Most votes
- Most comments
The reason why the CPU credit balance is not increasing is because the Instance type is configured with unlimited mode for CPU credits. If a burstable performance instance configured as unlimited depletes its CPU credit balance, it can spend surplus credits to burst beyond the baseline. When its CPU utilization falls below the baseline, it uses the CPU credits that it earns to pay down the surplus credits that it spent earlier. So in simpler terms, T3 instances can go 'negative' on CPU credits if they need to.
The CPU Credit Balance will increase after the surplus credits are paid off as the instance continues to operate under the baseline.
[1] Key concepts and definitions for burstable performance instances - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-credits-baseline-concepts.html
[2] Unlimited Mode for Burstable Performance Instances - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-performance-instances-unlimited-mode.html
[3] Monitoring Your CPU Credits - https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-performance-instances-monitoring-cpu-credits.html?shortFooter=true
Thank you for your reply. Do you mean I am currently with invisible "CPU credit debt" that the balance will not go up until it is completely paid off with the hourly earned credits?
But it doesn't make sense, because I have already been charged for the extra CPU utilization. I already paid for it with my money, why should I pay for another time with my future CPU credits?
Relevant content
- asked 2 years ago
- asked a year ago
- Accepted Answerasked 2 years ago
AWS OFFICIALUpdated 2 years ago- AWS OFFICIALUpdated 3 years ago
- AWS OFFICIALUpdated 3 years ago
- AWS OFFICIALUpdated a year ago
What’s your CPU usage?
As stated above, during that few hours the CPU usage is continuously below 1%.
Just an update, after 1X hours, the CPU credit balance finally climb up again according to the latest CPU credit usage. Apparently the "invisible CPU credit debt" has been paid off by then.