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Can someone explain how the cpu usage is calculated inside pods with multiple containers for use with an Horizontal Pod Autoscaler? Is it the mean value and how is this calculated?

For example: If we have 2 containers:

  • Container1 requests 0.5 cpu and uses 0 cpu
  • Container2 requests 1 cpu and uses 2 cpu

If we calculate both seperatly and take the mean: (0% + 200%)/2 = 100% usage?

If we take the sums and take the mean: 2/1.5 = 133% usage?

Or is my logic way off?

Maarten V.
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2 Answers2

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As of kubernetes 1.9 HPA calculates pod cpu utilization as total cpu usage of all containers in pod divided by total request. So in your example the calculated usage would be 133%. I don't think that's specified in docs anywhere, but the relevant code is here: https://github.com/kubernetes/kubernetes/blob/v1.9.0/pkg/controller/podautoscaler/metrics/utilization.go#L49

However, I would consider this an implementation detail. As such it can easily change in future versions.

Maciek Pytel
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In the Horizontal Pod Autoscaling design documentation it's clearly written that it takes the arithmetic mean of the pods' CPU utilization to compare against the target value. Here is the text:

The autoscaler is implemented as a control loop. It periodically queries pods described by Status.PodSelector of Scale subresource, and collects their CPU utilization. Then, it compares the arithmetic mean of the pods' CPU utilization with the target defined in Spec.CPUUtilization, and adjusts the replicas of the Scale if needed to match the target (preserving condition: MinReplicas <= Replicas <= MaxReplicas).

The target number of pods is calculated from the following formula:

TargetNumOfPods = ceil(sum(CurrentPodsCPUUtilization) / Target)

For further detail: https://github.com/kubernetes/community/blob/master/contributors/design-proposals/autoscaling/horizontal-pod-autoscaler.md

Anshul Jindal
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    If I understand correctly this info is about how to calculate how many pods the HPA needs to start. It does not state how it calculates the pod cpu usage if multiple containers are inside the pod. I think my question still stands. – Maarten V. Jan 09 '18 at 18:32
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    This describes how the autoscaler takes into account the CPU usage of each pod in a set of pods, not of each container in a set of pods. – Matt Welke Jul 06 '20 at 16:36