VPA: Usage of external metrics in recommender

[isioannou]

Currently, there is not any official reference regarding the ability of VPA to use external metrics. The only point that someone could find relevant info are this merged pr: #5576 and through source code https://github.com/kubernetes/autoscaler/blob/vertical-pod-autoscaler-1.3.0/vertical-pod-autoscaler/pkg/recommender/main.go#L87

My question is why there is not officially documented anywhere this feature , followed by some explanation/examples of how it could be also configured.

[adrianmoisey]

/area vertical-pod-autoscaler

That's a good question. The feature is marked as "Alpha", and I assume none of the current maintainers have the appetite to work on it, so that puts it in an awkward state where it doesn't get improved on.