Switch to promhttp handler and continue on error

[vbatoufflet]

Hi all,

This PR follows a discussion started in #56 and use the new HTTP handler provided by the promhttp package along with the promhttp.ContinueOnError error handler to prevent inconsistent metrics from preventing the whole scraping.

Please let me know if this requests suits you or if I missed something here.

Regards.

[brian-brazil]

When cAdvisor did similar in google/cadvisor#1679 it ended up making the scrape succeed, but instead started returning arbitrary subsets of the metrics.

[vbatoufflet]

Indeed, the metric not matching the stable label length criterion isn't sent anymore.

Wouldn't it be better that I make this behavior configurable via a command-line argument?

[brian-brazil]

I don't think it's a good idea to add a --randomly-break flag, the way to handle this is to fix the labels.

[vbatoufflet]

Ok I understand.

When you say fix the label. You mean in collectd_exporter or upstream in collectd?

[brian-brazil]

Wherever it needs to be fixed, I'm not too familiar with this part of collectd.

[vbatoufflet]

Ok, so I'll close this PR keeping the original issue regarding the incompatibility open.

[beorn7]

Indeed, the metric not matching the stable label length criterion isn't sent anymore.

Yes, that's the idea behind the option. The client library is designed to never create invalid output, thus it can only fail completely or leave out the offending parts.

[vbatoufflet]

Indeed @beorn7, I implemented this change exactly for that purpose as I can't use the collectd_exporter at the moment with collectd instances exporting conntrack data.

I'll use my own version for tests waiting to find a proper fix that suits everyone to make the exporter compatible with collectd's way to export such metrics trough its binary protocol.

[brian-brazil]

Have you considered using collectd's own Prometheus metrics output? It lacks this sanity checking.

[vbatoufflet]

I must admit that I wasn't aware of its existence. Thanks! I'll take a look at it.