removing _total prefix from nginx guage metrics

[noqcks]

What this PR does / why we need it: This fixes #1509. We want to be following best practices! https://prometheus.io/docs/practices/naming/

Which issue(s) this PR fixes:
Fixes #1509 and corrects #1910

Release note:

action required: Changed the names of default Nginx ingress prometheus metrics. If you are scraping default Nginx ingress metrics with prometheus the metrics changes are as follows
nginx_active_connections_total -> nginx_connections_total{state="active"}
nginx_accepted_connections_total -> nginx_connections_total{state="accepted"}
nginx_handled_connections_total -> nginx_connections_total{state="handled"}
nginx_current_reading_connections_total -> nginx_connections{state="reading"}
nginx_current_writing_connections_total -> nginx_connections{state="writing"}
current_waiting_connections_total -> nginx_connections{state="waiting"}

I'm not sure if we would like to remove the current_ prefix from the gauges if that's implied without some kind of total prefix, but I think this fixes the issues @discordianfish and @brancz had with #1910.

Side note: does this need some kind of release note action to notify people using these metrics since it could break their monitoring/alerting?

tagging @kubernetes/sig-instrumentation-pr-reviews for input.

[k8s-reviewable]

This change is 

[k8s-ci-robot]

@noqcks: Reiterating the mentions to trigger a notification:
@kubernetes/sig-instrumentation-pr-reviews

In response to this:

What this PR does / why we need it: This fixes #1509. We want to be following best practices! https://prometheus.io/docs/practices/naming/

Which issue(s) this PR fixes:
Fixes #1509 and corrects #1910

NONE

I'm not sure if we would like to remove the current_ prefix from the gauges if that's implied without some kind of total prefix, but I think this fixes the issues @discordianfish and @brancz had with #1910.

tagging @kubernetes/sig-instrumentation-pr-reviews for input.

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.

[noqcks]

/assign @brancz

[SuperQ]

I would suggest removing current_, this is implied because metrics are always "current".

[SuperQ]

I might actually reverse these metrics.

ingress_class_connections_reading

But, thinking more, is it valid to sum() up these metrics? So they should be labeled?

ingress_class_connections{state="reading"} X
ingress_class_connections{state="writing"} X
ingress_class_connections{state="waiting"} X

[piosz]

FYI @loburm

[coveralls]

Coverage increased (+0.1%) to 36.822% when pulling 0d93f20 on noqcks:correcting-metric-names into 8079322 on kubernetes:master.

[aledbf]

Side note: does this need some kind of release note action to notify people using these metrics since it could break their monitoring/alerting?

We need to add a note in the breaking section of the release notes.
Before we merge this can you add a comment with the changes?

[aledbf]

@noqcks you can use gofmt -w -s internal/ingress/controller/metric/collector/nginx.go to fix the style issues
Also please squash your commits

[noqcks]

Nice, thanks @aledbf

Ok. I updated this PR and I think it makes sense based on the feedback from @SuperQ

cc: @brancz @discordianfish

[coveralls]

Coverage increased (+0.1%) to 36.837% when pulling c9e0b6b on noqcks:correcting-metric-names into 07c2bb8 on kubernetes:master.

[aledbf]

@noqcks please squash the commits

[aledbf]

@noqcks is this PR ready to be reviewed/merged?

[noqcks]

squashed commits. ready for review @aledbf

[aledbf]

@brancz @discordianfish please review
Thanks!

[SuperQ]

LGTM

[aledbf]

@SuperQ sorry I forgot to add you in the comment :)
Thanks for the help and LGTM

[coveralls]

Coverage increased (+0.01%) to 36.88% when pulling fae55e8 on noqcks:correcting-metric-names into 5a16a7a on kubernetes:master.

[brancz]

/lgtm

[aledbf]

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aledbf, brancz, noqcks

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[discordianfish]

Awesome, that was quick!