servenv: Move away from using default HTTP muxer

[dbussink]

Up until now we've been using the implicit default HTTP mux. The problem of using this mux is that it works implicitly also for profiling endpoints. So the moment that net/http/pprof is imported, those endpoints get added.

We want to be able to make enabling the profiling endpoints optional, but there's no way to do that with the default mux except by recompiling and removing the import.

By moving everything away from the default mux to an explicit mux for the servenv, we can make this configurable in the near future. It still gets added to the default mux, but we don't use that anymore so it doesn't get exposed.

The changes here now explicitly add the profiling endpoints so that we can make that optional in a follow up.

Checklist

• "Backport to:" labels have been added if this change should be back-ported
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[vitess-bot]

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[frouioui]

@dbussink looks good to me besides two comments.

What are we using the profiling endpoints for? I remember us having go/vt/servenv/pprof.go which allows us to profile Vitess, will the pprof feature no longer work?

[ajm188]

this is awesome! i have one suggestion around structuring, but otherwise i'm extremely excited about this

[ajm188]

🎉

[dbussink]

What are we using the profiling endpoints for? I remember us having go/vt/servenv/pprof.go which allows us to profile Vitess, will the pprof feature no longer work?

Because of the http pprof import that exists today and our usage of the default mux, we always end up with the http profiling endpoints today.

It’s not possible to turn those off and on because of that.

Anyone using Vitess could be using those endpoints to enable / disable specific profilers at runtime through those pprof http endpoints. We use these for example in PlanetScale internally when we need to debug issues with Vitess to do things like dump stack traces for goroutines.

That’s separate from the profiling flags which end up always enabling the profiling depending on how those flags are given. So they are separate things today.

The net change of the refactor here is that for the end user everything still works the same.