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Add histogram exemplar support #124013

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Add histogram exemplar support #124013

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richabanker
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@richabanker richabanker commented Mar 20, 2024 •
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What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds exemplar support for histograms

Which issue(s) this PR fixes:

Fixes #119697

Does this PR introduce a user-facing change?

NONE

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

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@richabanker richabanker mentioned this pull request Mar 20, 2024
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rexagod
rexagod reviewed Apr 8, 2024
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staging/src/k8s.io/component-base/metrics/metric.go Outdated
func (noopMetric) Set(float64) {}
func (noopMetric) Sub(float64) {}
func (noopMetric) Observe(float64) {}
func (noopMetric) ObserveWithExemplar(float64, prometheus.Labels) {}
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I'm revisiting this after a good while but IIRC from a discussion with @logicalhan around exemplar support for counters, we want to modify the existing methods implicitly (without modifying their signatures) to support exemplars OOTB.

Additionally, my understanding is that we don't want to make any component directly dependent on prometheus/client_golang, but incorporate that behavior into component-base and have them import that instead, in an effort to be able to offset any breaking changes and not having to send patches upstream (and catering to any extra use-cases specific to k/k).

All components themselves will be responsible for "attaching" exemplars within their contexts, if they want to utilize this feature-set, but we won't have to make any explicit changes in any component for this feature-set to work. However, the SIG can help components benefit from this by patching their contexts for them, but I believe that is out of the scope of this effort (adding exemplar support to component-base).

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Thanks for the pointers @rexagod. The initial version of this PR was mostly a POC to verify that we are able to see exemplars after-all in metrics, hence admittedly had quite a lot of hacky stuff going on at first.

I modified this PR now, following what you are doing for counters in #119949, though it still needs to use the component-base.metrics.exemplarMetric that you have introduced, so I'll wait for that PR to merge first and make those changes then.

Additionally I am wondering, if we need to introduce Add()/Observe() methods for CounterVec/HistogramVec too?

@richabanker richabanker marked this pull request as ready for review April 18, 2024 16:04
@k8s-ci-robot k8s-ci-robot removed the do-not-merge/work-in-progress Indicates that a PR should not merge because it is a work in progress. label Apr 18, 2024
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logicalhan
logicalhan reviewed Apr 18, 2024
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/assign
/triage accepted

@k8s-ci-robot k8s-ci-robot added triage/accepted Indicates an issue or PR is ready to be actively worked on. and removed needs-triage Indicates an issue or PR lacks a `triage/foo` label and requires one. labels Apr 18, 2024
dashpole
dashpole reviewed May 3, 2024
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lgtm with one nit

staging/src/k8s.io/component-base/metrics/histogram.go Outdated
Comment on lines 42 to 49
h.withExemplar(v)
}

func (h *Histogram) withExemplar(v float64) {
(&exemplarHistogram{h}).withExemplar(v)
}

func (h *exemplarHistogram) withExemplar(v float64) {
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Why do you need the extra exemplarHistogram type and the withExemplar functions.

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Good catch, I don't. Can't remember why I did that, removed it now.

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[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: richabanker
Once this PR has been reviewed and has the lgtm label, please ask for approval from logicalhan. For more information see the Kubernetes Code Review Process.

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dashpole
dashpole reviewed May 30, 2024
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same comments for exemplarHistogramVec

staging/src/k8s.io/component-base/metrics/histogram.go
"span_id": maybeSpanCtx.SpanID().String(),
}
}
if m, ok := h.ObserverMetric.(prometheus.ExemplarObserver); ok {
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is this always going to be true? Should we fall back to the regular observe if it isn't an examplar observer?

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I am not sure... but still, added a fallback to use the regular Observe() flow.

staging/src/k8s.io/component-base/metrics/histogram.go Outdated
}

func (h *Histogram) withExemplar(v float64) {
var exemplarLabels prometheus.Labels
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Should we move this inside the if statement below to avoid unnecessary computation?

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Sounds good, moved.

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same comments for exemplarHistogramVec

I need to wrap the return value of func (vc *HistogramVecWithContext) WithLabelValues(lvs ...string) which is currently ObserverMetric into a struct on which I could apply func withExemplar(). So the extra exemplarHistogramVec is needed for exemplarHistogramVec.

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@richabanker: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name Commit Details Required Rerun command
pull-kubernetes-integration a73152a link true /test pull-kubernetes-integration

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Trace exemplars for kube-apiserver metrics
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