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This patch refactors the metrics support within fabio to achieve several goals: * support labels for DogstatD, Prometheus and others * support raw events for statsd and others without aggregation * support multiple backends simultaneously to support migration * make integration of new metrics backends and/or libraries simple * being fully backwards compatible to not break existing setups One of the main challenges is that fabio generates names for the metrics targets through templates and that these templates are configurable. A metrics backend which supports labels needs to generate a different name for the same metric than one that does not support labels. Combining this with the need to support multiple different metrics backends at runtime means that none of the existing metrics libraries like go-kit/metrics and hashicorp/go-metrics is a good fit. However, they can be used as drivers which reduces the need for testing and makes integration of new backends simpler since fabio does not need to rely on a single metrics library. This patch is work in progress with the new metrics code in the metrics4 package and the old metrics code in the 'metrics_old' package where it is kept for reference until it has been migrated or removed. The basic architecture should be good enough to add more providers and functionality so that the community can help. Right now there are two providers "flat" and "label" to demonstrate the concepts. They provide counter and timers in statsd/dogstatd format and can be configured with -metrics.target=flat[,label]. Other providers should be added in the same way. The metrics_old code should be converted to the new provider scheme. The go-kit/metrics library currently supports most of the necessary drivers and is the preferred way of integrating new drivers. The list below is a probably incomplete list of things that need to be done: * The configuration is not used except for metrics.target * The drivers from the metrics_old package need to be migrated * Additional drivers from go-kit need to be added * The old rcrowley/go-metrics code relies on 'registries' for namespacing. After the routing table has changed the registry needs to be pruned of services which no longer exist so that go-metrics stops reporting them. * The RX/TX counters in the TCP and TCP+SNI proxy are probably sub-optimal or broken. * Some counters may not have been initialized properly, e.g. WSConn * WSConn should probably be a gauge which also needs to be set to 0 on startup. * The approach of injecting a noop metrics provider if none has been set has already bitten me once since some metrics are reported while others are not. I need to think about this a bit more. Fixes #126 Fixes #165 Fixes #211 Fixes #253 Fixes #326 Fixes #327 Fixes #371 Closes #329 Closes #331 Closes #334 Closes #335 Remove 'Register' methods and create objects directly. Add Gauge and use it for websocket connections Vendoring in github.com/alexcesaro/statsd First stab at integrating raw statsd from #335 Rebase off master 10/23/2020 - NJ
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