The Keptn metrics server is a tool which enables developers to retrieve metrics from any / many sources, store them in an on-cluster cache and treat them completely generically. You no longer need to worry about where they came from, just “get me the value of metric foo” regardless of the metric source.
I’ve wrote this as a hands-on blog over on dev.to: Hands on with Keptn Metrics Server: Pull Metrics from anywhere and treat them generically.