[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3786: Add OpenMetrics-format endpoint for scraping with Prometheus

[Tahoe-LAFS]

#3786: Add OpenMetrics-format endpoint for scraping with Prometheus
-------------------------------+---------------------------
 Reporter:  hacklschorsch      |          Owner:
     Type:  enhancement        |         Status:  new
 Priority:  normal             |      Milestone:  undecided
Component:  code-frontend-web  |        Version:  unknown
 Keywords:  statistics         |  Launchpad Bug:
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 I am creating monitoring infrastructure for the upcoming
 [https://private.storage/ PrivateStorage SaaS].
 I'd like to add an [https://openmetrics.io/ OpenMetrics] format statistics
 endpoint to be scraped by [https://prometheus.io/ Prometheus].

 The de-facto industry standard Prometheus scrapes metrics endpoints that
 by default are available on the things under monitoring on some HTTP
 server under {{{/metrics}}}.

 I see there's already a {{{/statistics?t=json}}} endpoint that seems very
 similar to what I want to build, and also lots of useful things in
 {{{misc/operations_helpers/munin}}}.
 My plan so far is to add a `/statistics?t=openmetrics` endpoint exporting
 the same values as the json, but in OpenMetrics.

 In the #tahoe-lafs IRC channel on Libera:

 {{{
 hacklschorsch | Does that make sense?  Is there a better way?
          jpds | hacklschorsch: Yes, a /metrics endpoint would be great
      itamarst | hacklschorsch: that sounds plausible to me
 }}}

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3786>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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