Lightsail burst capacity questions

Question

Hi.

I'm using a Lightsail Debian instance for couple of days now, working just fine.

Questions about the burst capacity:
1- What If my instance accidentally runs constantly at 100% of CPU utilisation ?  What will happened after the instance had burned all its burst capacity ?  Is AWS will drop down the utilisation to the baseline performance accordingly to the instance provisioned plan ?  ie: Can an instance runs at 100% of cpu time 24/7 ?  if yes, what is the use for the bursting capacity ?  FYI - I know that my instance would be unusable as all its cpu capacity will just be used, just curious.

2- How other instances bursts can negatively affect my instance ?  Knowing that lightsail instances are using shared CPU within Xen hypervisors, is other instances bad performances located on the same hypervisor can negatively affect my own instance performances ? 2b- Should I worried about my instance "cpu steal time" metric ?

Thanks.

Answer

Hi.

### 1 What If my instance accidentally runs constantly at 100% of CPU utilisation ?
Keep the vCPU average below the baseline during normal times.  
If you cross the baseline, you will consume burst credits.  
And Lightsail instances that are depleted of burst credits will slow down to baseline. It can be used 24 hours a day, 7 days a week, but it cannot handle high-load conditions because there is an upper limit on the CPU usage rate.

Rodney mentions additional payments, but I think this is the case for EC2.  
With EC2, you can choose between slowing down to baseline when you run out of burst credits, or paying an extra fee to keep bursting.

In the case of Lightsail, there is no unlimited function when using EC2 burst credit, so CPU usage is limited to the baseline.

You will find the following article helpful.  
https://lightsail.aws.amazon.com/ls/docs/en_us/articles/amazon-lightsail-viewing-instance-burst-capacity

### 2 How other instances bursts can negatively affect my instance ?
As mentioned above, you are calculated and limited by the average vCPU assigned to you on the virtual machine. Therefore, there is no need to consider the adverse effects of other users.

Answer

You will end up paying for the additional capacity. See https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/burstable-credits-baseline-concepts.html

You can monitor the burst capacity by following the steps in this blog:
https://aws.amazon.com/blogs/compute/proactively-monitoring-system-performance-on-amazon-lightsail-instances/

Lightsail burst capacity questions

1 What If my instance accidentally runs constantly at 100% of CPU utilisation ?

2 How other instances bursts can negatively affect my instance ?

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