cri_stats_provider: do not consider exited containers when calculating cpu usage

[ashleycutalo]

What type of PR is this?
/kind bug

What this PR does / why we need it:
When using the cri_stats_provider with cri-o, the current implementation of remove_terminated_containers() causes the kubelet to report inaccurate stats for pods that have terminated and restarted containers, for example during a crashloop, such as:

NAME                      CPU(cores)       MEMORY(bytes)              
crashy-784977b697-pjnsr   1800454008594m   3Mi             

This in turn causes undesired behavior in the HPA, as it reports seeing an unrealistically high cpu usage and scales up to max:

NAME              REFERENCE                    TARGETS          MINPODS   MAXPODS   REPLICAS   AGE
crashy-main       Deployment/crashy-main       263322784%/50%   5         20        20         175d

This is because the calculation for usageNanoCores subtracts the cached UsageCoreNanoSeconds (a nonzero number) from the newly observed UsageCoreNanoSeconds (which is set to zero for an exited container), resulting in a nonsensical number. Note that the check for zero or negative interval will not trip in this case, as the timestamp will continue to be nonzero and increasing.

Removing all exited containers from the cpu usage calculation fixes this issue. All exited containers will report 0 for UsageNanoCoreSeconds and therefore will never be significant when calculating cpu usage for the pod, so they should be removed from consideration.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

NONE

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[vllry]

/cc

[vllry]

Nitpick: “terminated” and “not running” aren’t the same thing: https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#container-states

[ashleycutalo]

What is the suggestion here? Rename the function? From a logical perspective, only "running" containers are consuming resources, so only running containers should be used when calculating pod resource usage. "Waiting" containers should also be excluded, as they are also not consuming resources.

[vllry]

/priority important-soon

[mattjmcnaughton]

Welcome to the k8s project :) thank you for the diff!

/ok-to-test

I agree with @vllry's nit, but other than that, this makes a lot of sense to me.

[vllry]

/assign @dashpole

[vllry]

I did some more digging, and I think a lot of this function can be removed.

I can only find 2 references to removeTerminatedContainers, and neither use the fact that the output is sorted (by container ID and by create time). Because of that, I think we can remove the whole map and sort process.

@mattjmcnaughton am I barking up the wrong tree?

[ashleycutalo]

This was originally added in the cadvisor_stats_provider as a fix for #47853. Its primary functionality was for deduping due to a race condition between cadvisor and cgroup removal. If deduping is no longer necessary (fwiw I have not observed this race condition happening between crio and cgroups), this function can indeed be greatly simplified. I did some searching through the commit history and was unable to determine why the deduping functionality was ported forward from cadvisor_stats_provider when cri_stats_provider was added. I have preserved the deduping logic to minimize the impact of this diff, but personally I feel this can probably be removed as well.

[ashleycutalo]

/retest

[ashleycutalo]

/retest

[ashleycutalo]

/retest

[dims]

/assign @yujuhong
/milestone v1.18

[dashpole]

/lgtm
/approve
This seems reasonable to me

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ashleykasim, dashpole

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