Delay init of http phase values

[SuperQ]

Don't init http probe phase labels until we're ready to send the
request.

Avoids exposing 0 value samples for things we haven't started to
measure.

Fix http resolve timing to report lookup time even if it's an error
(ie not found).

Fixes: #579

Signed-off-by: SuperQ superq@gmail.com

[roidelapluie]

Mmmmh that's an interesting PR, it means that averages etc will only work when a phase is executed, I am not sure we should do this.

[SuperQ]

@roidelapluie It's a difficult choice. The problem is we emit 0 for things we have explicitly not measured, which is what the original issue is about.

[roidelapluie]

Why this is a problem: if you perform any analytics over those metrics (eg percentiles, or min) it would be skewed.

But if probe_success == 0 you should not run analytics over them either.

[zerkms]

@roidelapluie

But if probe_success == 0 you should not run analytics over them either.

how would you exclude those series that were obtained with an error

[roidelapluie]

I've been thinking this further.

When HAProxy Exporter can not scrape HAProxy, it does not return zero-ed metrics. We should do the same here.

[SuperQ]

I also added a fix for the "resolve" phase. It now accounts for the resolve phase time even if the resolve result is a failure.

[roidelapluie]

Thanks!