t3a high cpu utilisation compared to t3
As an experiment, I stopped a t3.nano instance and restarted it as t3a.nano
Normally the CPU utilisation is around 3%, but it shot up to 8%, above the baseline ( mean the CPU credit balance started to fall ).
I don't understand why there would be such a big difference in CPU utilisation. There isn't a lot going on on this server apart from windows overhead, other than curl jobs running off windows task scheduler every 10 minutes.
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The difference in CPU utilization you're observing between t3.nano and t3a.nano instances is likely related to the underlying processor architecture differences between these instance types.
T3a instances use AMD EPYC processors, while standard T3 instances use Intel processors. These different CPU architectures can result in varying performance characteristics for the same workload, even when the instance size remains the same. The AMD processors in t3a instances might handle your specific workload differently than Intel processors, resulting in the higher CPU utilization you're seeing.
For burstable instance types like t3.nano, this difference is particularly important because they operate on a CPU credit model with a baseline utilization of 5% (for t3.nano). When your utilization exceeds this baseline (as you're seeing with 8% on the t3a.nano), the instance starts consuming CPU credits, which can eventually lead to performance constraints once those credits are depleted.
While t3a instances are designed to be a more cost-effective alternative to t3 instances (typically about 10% cheaper), this cost savings might be offset by higher CPU utilization for certain workloads, potentially leading to faster credit depletion.
If maintaining a steady credit balance is important for your use case, you might want to consider:
- Switching back to the t3.nano instance
- Upgrading to a larger instance size with a higher baseline
- Investigating if there are any specific Windows processes or scheduled tasks that might be performing differently on the AMD architecture
Sources
High CPU Usage on an Idle MSSQL RDS database | AWS re:Post
DAX T3/T2 burstable instances - Amazon DynamoDB
Key concepts for burstable performance instances - Amazon Elastic Compute Cloud
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