Monitoring of prometheus-adapter metrics

[matthewjstanford]

What happened?:

I've got a set of custom metrics defined in prometheus-adapter. I was refactoring the source metrics in Prometheus (modifying labels) and inadvertently broke one of the custom metric in prometheus-adapter.

This specific custom metric was used by an HPA, along with CPU & Memory. When the custom metric stopped responding (returning a 404) the HPA went into the weeds and scaled the deployment way up. I believe this is mostly a bug in how the HPA handles missing metrics, but this really begs the question, how can I monitor the health of custom metrics provided by prometheus-adapter?

What did you expect to happen?:

I expected the prometheus-adapter to emit prometheus metrics itself. Something along these lines:

example metrics

# TYPE prometheus_adapter_custom_request_status_total gauge
prometheus_adapter_custom_request_status_total{metric="my_custom_metric", status="200"} 1
prometheus_adapter_custom_request_status_total{metric="my_inalid_custom_metric", status="404"} 2

# TYPE prometheus_adapter_external_request_status_total gauge
prometheus_adapter_external_request_status_total{metric="my_external_metric", status="200"} 5
prometheus_adapter_external_request_status_total{metric="my_invalid_external_metric", status="404"} 6

But I don't believe prometheus-adapter emits any metrics (hopefully I'm wrong!).

Having info like this would enable the ability to actively monitor the availability of critical custom metrics, such as the ones discussed above.

[matthewjstanford]

It looks like I can monitor the availability of the prometheus-adapter metrics via a Horizontal Pod Autoscaler metric, kube_horizontalpodautoscaler_status_target_metric.

This is a bit backwards, IMO, but it at least provides a mechanism to monitor the metrics.

[dgrisonnet]

/triage accepted
/assign

[pznamensky]

Same for us - we've broken an external metric and got to know about it after several days. It would be great to somehow monitor prometheus-adapter itself.