metrics: allow disabling OpenMetrics negotiation

[hairyhenderson]

Fixes #3940 by allowing users to disable OpenMetrics negotiation. This shouldn't usually be necessary, but there's a couple of incompatible metric names in the upstream Go collector which break strict parsing. I'll also log a bug in prometheus/client_golang and link it here.

Documentation PR is here: caddyserver/website#123

Signed-off-by: Dave Henderson dhenderson@gmail.com

[hairyhenderson]

Not sure why goreleaser-check is failing - @francislavoie @mohammed90 any ideas?

[mohammed90]

@hairyhenderson the failure is due to deprecation notices. See https://goreleaser.com/deprecations#nfpmsfiles and https://goreleaser.com/deprecations#nfpmsconfig_files

@francislavoie fixed it in:

8286f8d

[francislavoie]

Sorry about that - I cherrypicked it into #3945 and I'll merge it asap, no use just leaving it in my unrelated PR.

[francislavoie]

Okay merged, you could rebase to re-run CI if you like.

[hairyhenderson]

Alright - rebased!

[mholt]

Thanks Dave!

Oof, the golang prometheus client is getting heavier and heavier :(

I don't love having such a deep dependency chain. Something we will have to come back and address later probably.

[hairyhenderson]

Oof, the golang prometheus client is getting heavier and heavier :(

I don't love having such a deep dependency chain. Something we will have to come back and address later probably.

There's a related conversation in the prometheus/common repo (where most of the new dependencies come from I think): prometheus/common#255 - my impression is many of those dependencies aren't really that relevant since they don't end up in the final binary.

[mholt]

Thanks for linking that.

my impression is many of those dependencies aren't really that relevant since they don't end up in the final binary.

And that's good, but it still makes pulling repos really slow and tedious. And easier for things to break then, which makes development hard. Anyway, I commented in that issue.

[mholt]

LGTM. Will merge momentarily and cut rc2 to test the updated CI pipeline