Implement number of HTTP frames metric

[nerodono]

Implements metric described in linkerd/linkerd2#12319

[loyd]

@nerodono, it seems some test can be added to linkerd/app/integration/src/tests/telemetry.rs

[loyd]

@olix0r, could you look at this PR?

[olix0r]

Thanks for submitting this. There is work in flight (planned to merge soon) that will add route metrics. My preference would be to add this functionality here so that we can include parent/route/backend labels on these metrics. I'll update this PR when that is available.

[loyd]

There is work in flight (planned to merge soon) that will add route metrics

Is there any news regarding this? I really don't want to live on a fork =(

[olix0r]

The first version of it has merged but it's not in a place where the frame metrics are really setup. We, coincidentally, had some reports of issues related to applications sending many very small frames, and so I'm planning to introduce a per-route data_size histogram so we can understand both the count of data frames transiting the proxy as well as a rough distribution of their sizes. This work was slightly delayed by some travel, etc. (so please excuse the silence), but it is actively being worked on as of this week. I'll update here when there is something to show.

[loyd]

per-route data_size histogram

It sounds very useful, actually! Which GH issue is related to this work?