scrape becomes slower with more backends

[hsmade]

• Varnish 6.3.1
• prometheus_varnish_exporter 1.5.1

---

As the metrics are fetched from varnish during a scrape request, the scraping gets slower with more backends. Due to that old backends are not removed (for a while), the number of backends can increase quickly in a CI/CD environment. This causes scrapes to take longer, and take up resources in prometheus.
Generally what you'd want to do in a 'heavy' scraper as this one, is fetching metrics on a Timer.Tick and keeping them. If you fail to get metrics on the next tick, you can empty the cache as well, to signal to prometheus that something failed.

[blackjid]

@hsmade did you find a way to setup this exporter that improve perfomance on metrics scraping??