Add metrics endpoint for buildkitd

[jsravn]

It would be great if buildkitd exposed metrics that can be used to monitor it and debug issues.

Some useful metrics:

• Build cache size
• Build statistics per client

[jsravn]

For per client statistics, it could use the client name in the client TLS certificate if used. Otherwise, maybe some metadata could be passed with the build request.

[jsravn]

I was thinking about this more in the context of a Kubernetes cluster. A problem for registering metrics is buildkit does not know about the context (who is doing the build), so the metrics will have to be quite general. Would be acceptable to add Kubernetes support, such that buildkitd could determine the calling pod information from the peer IP on the gRPC request?

[alsterg]

+1

[errordeveloper]

@jsravn is it correct to assume that you are implying Prometheus exposition format?

[jsravn]

@jsravn is it correct to assume that you are implying Prometheus exposition format?

Yes, or I suppose openmetrics these days.

[halvorstein]

@jsravn Hi. Have you managed to find a workaround for this issue?