[RFC] Diversify and standardize Sentinel metrics and monitoring

[sczyh30]

Issue Description

Type: feature request

Describe what feature you want

Currently the metrics and monitoring of Sentinel is not standardized and versatile enough. This issue will discuss about standardization and improvements of metrics and monitoring of Sentinel, so that we can enable:

• provide standard and diverse metrics representation (e.g. percentile, gauge, histogram)
• standardization of monitoring API and transport server API, and adapt to open-source monitoring components (e.g. Prometheus)
• integration with open-source visualization solution (e.g. Grafana) in Sentinel Dashboard

Suggestions are welcomed :)

[CarpenterLee]

Sentinel has being tracing every method call in it's context, so the simplest way enhance the metric is to add some callbacks to inform the existing metic implementation, such as Ali-metric or Prometheus.

Since diversifying the metrics is not the main feature of Sentinel(which is flow controlling and shaping), the standard metric feature should be pluggable and replaceable. So we may need anther Sentinel extension to do this work.

[XiaoWeiKIN]

hi，what's going on now?