Improve apiserver SLI metric name

[dgrisonnet]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Add new kube-apiserver SLI metric better reflecting that the metric is
an SLI and not an SLO and deprecate the existing
apiserver_request_slo_duration_seconds in 1.27. Although the metric is
still in alpha, we prefer deprecating it for one release since it is a
critical metric used for SLOs and to make sure that users that are using
it have time to make the transition.

Going forward we prefer going with SLI-specific metrics, we will use
sli instead of slo so for consistency purposes.

Does this PR introduce a user-facing change?

Deprecate the apiserver_request_slo_duration_seconds metric for v1.27 in favor of apiserver_request_sli_duration_seconds for naming consistency purposes with other SLI-specific metrics and to avoid any confusion between SLOs and SLIs.

[dgrisonnet]

/assign @logicalhan

[dgrisonnet]

/sig instrumentation

[logicalhan]

Even though this is alpha, I'm hesitant to rename it because I actually suspect people have already started using it.

[dgrisonnet]

Yes, there should already be quite a huge amount of users since the whole ecosystem that imports https://github.com/kubernetes-monitoring/kubernetes-mixin is already using this metric.

My main reason for changing the name is that metrics are hard to discover by default since we don't have a solid documentation upstream. So the principal way to discover metrics is to look for certain patterns in the query platform. Let's say a user is looking for SLI metrics, then by searching for the sli pattern if our metrics have consistent names then they should get all our SLI-related metrics.

As for actually breaking the users, I think it should be fine since the metric is still ALPHA and I labeled this PR as an API change so it will appear as a breaking-change in the changelog.

[k8s-triage-robot]

This PR may require API review.

If so, when the changes are ready, complete the pre-review checklist and request an API review.

Status of requested reviews is tracked in the API Review project.

[fedebongio]

/triage accepted

[logicalhan]

As for actually breaking the users, I think it should be fine since the metric is still ALPHA and I labeled this PR as an API change so it will appear as a breaking-change in the changelog.

Absolutely not, I am not in favor of just breaking users. Instead, we should introduce a second metric and deprecate this one and give people an actual chance to migrate.

[dgrisonnet]

/kind cleanup

[logicalhan]

/assign @wojtek-t

[dgrisonnet]

@logicalhan makes sense, I addressed your comment.

@wojtek-t can you please also take a look?

My main concern now that we have added a deprecation period is that we will have to live with 3 SLO metrics in 1.26 which will increase the number of timeseries exposed by Kubernetes by quite a lot since these metrics are already the most expensive one. We can expect to have users complaining about the increase, but since it is only for one release, I guess it should be fine.

[logicalhan]

lgtm but i also share cardinality concerns.

@wojtek-t what do you think?

[wojtek-t]

lgtm but i also share cardinality concerns.
@wojtek-t what do you think?

Just to double check I didn't miss anything - it's effectively the exact same metric - just we're naming it differently?
Assuming I'm right, I agree with the cardinality concern, but I don't see a better way of doing that (if we really want to rename it which makes sense to me) - just switching the name sounds too problematic to me.

So I'm fine with that, but I would like to get an ACK from at least one of folks who use that extensively internally:
@mborsz @marseel

[dgrisonnet]

Yes this is just a renaming

[marseel]

/lgtm

[logicalhan]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: dgrisonnet, logicalhan

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files:

• staging/src/k8s.io/apiserver/pkg/endpoints/metrics/OWNERS [logicalhan]

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment