CFP: Add optional labelsContext to forward_count_total and forward_bytes_total metrics

[andreev-io]

Cilium Feature Proposal

Is your proposed feature related to a problem?

There have been requests to make it possible to measure flow bandwidth with Cilium/Hubble (#12913, #16188); however, this is still currently not possible.

Describe the feature you'd like

As far as I understand, Cilium already has information on packet counts and packet sizes, as indicated by the forward_count and forward_bytes metrics. Cilium also has information on Kubernetes metadata associated with a flow. Why not make it possible to annotate forward_bytes and forward_count metrics with this metadata (Kubernetes labels such as pod name at a minimum, L3 connection tuple parameters and Kubernetes labels as a goal)

(Optional) Describe your proposed solution

Please complete this section if you have ideas / suggestions on how to implement the feature. We strongly recommend discussing your approach with Cilium committers before spending lots of time implementing a change.

For longer proposals, you are welcome to link to an external doc (e.g. a Google doc). We have a Cilium Feature Proposal template to help you structure your proposal - if you would like to use it, please make a copy and ensure it's publicly visible, and then add the link here.

Once the CFP is close to being finalized, please add it as a PR to the design-cfps repo for final approval.

[andreev-io]

I was told in https://cilium.slack.com/archives/C1MATJ5U5/p1714051757203969 that the foward_count and forward_bytes metrics are not based on Hubble flow objects and are just based on device Tx/Rx counts.

Even if so, shouldn't it be relatively simple to create a new metric that allows measuring throughput based on Hubble flows? Flow objects themselves can be used as a measure of packet counts, and byte counts can be put into flow objects using the Extensions field.