Expose bouncer metrics through prometheus

What would you like to be added?

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/kind enhancement

Current prometheus endpoint for the LAPI does not provide detailed information about bouncer behaviour, only received requests by bouncer:

cs_lapi_bouncer_requests_total{bouncer="crowdsec",method="GET",route="/v1/decisions/stream"} 59
cs_lapi_bouncer_requests_total{bouncer="[email protected]",method="GET",route="/v1/decisions/stream"} 638

Why is this needed?

Considering that the LAPI is already receiving detailed metrics from bouncers specific to blocked requests, exposing this through Prometheus can be very useful to:

• Analyze/Track bouncer behavior
• Create alerts that determine if a bouncer is working (i.e. bounce rate < threshold)

Second item here is critical for availability and monitoring. It is very difficult right now to automatically asses if a bouncer is or not working to generate availability alerts.

This would also fix https://github.com/maxlerebourg/crowdsec-bouncer-traefik-plugin/issues/171