higher buckets for workqueue histograms

[seankhliao]

The workqueue subsystem exposes several metrics, including the workqueue_queue_duration_seconds and workqueue_work_duration_seconds buckets.
These currently have exponential buckets going from 1ns -> 10s.

controller-runtime/pkg/metrics/workqueue.go

Lines 53 to 65 in 1b80b96

	latency = prometheus.NewHistogramVec(prometheus.HistogramOpts{
	Subsystem: WorkQueueSubsystem,
	Name: QueueLatencyKey,
	Help: "How long in seconds an item stays in workqueue before being requested",
	Buckets: prometheus.ExponentialBuckets(10e-9, 10, 10),
	}, []string{"name"})
	workDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
	Subsystem: WorkQueueSubsystem,
	Name: WorkDurationKey,
	Help: "How long in seconds processing an item from workqueue takes.",
	Buckets: prometheus.ExponentialBuckets(10e-9, 10, 10),
	}, []string{"name"})

I think these should go up a further 2 steps to include 100s and 1000s as buckets (and maybe drop the lowest 2 buckets if we're concerned about the number), especially for workqueue_queue_duration_seconds as a stuck / poorly implemented controller can have quite high latency in processing reconciliation requests

[troy0820]

/kind support

[troy0820]

/kind feature

Would increasing the bucket size be beneficial to provide that info if that limit is never reached? I am not certain why these sizes were picked but 1000s seems a bit long and arbitrary to define for something that may not ever hit that limit. I'm interested in understanding why having these upper bounds would be helpful beyond the need to capture the high latency in the reconciliation requests.

[seankhliao]

You'd want the last defined bucket to be past the upper bound of what can be considered "reasonable" values to be able to estimate where the top end of the values you observe are (since monitoring system work by interpolating between bucket bounds to estimate percentiles). The +Inf bucket captures everything, but isn't useful for interpolation since it's infinity.

We regularly see "normal" queue latency on the order of 1-2 minutes for our larger clusters with controllers that need to make many external calls (not a great situation to be in) so placing the upper bound at the next step up (1000s) seems reasonable (and hopefully nothing normally operates at 1000s latency).

Aside: If prometheus ever stabilizes their native histograms (true expontnial), then we wouldn't need to choose these bucket bounds so carefully.

[troy0820]

I don't believe this will have any other implications where this would ruin anything from before, so I feel like this is a reasonable requests.

@sbueringer WDYT?

With this proposal to increase the buckets, pending buy-in from the maintainers, do you want to do the PR? @seankhliao

[seankhliao]

sure, I've sent #2638

[troy0820]

/close

Resolved #2638

[k8s-ci-robot]

@troy0820: Closing this issue.

In response to this:

/close

Resolved #2638

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.