Include pod UID and container name as optional trace labels

[sfleen]

It's useful to include these fields in the trace span attributes to help correlate traffic within a cluster.

This propagates these labels through the trace initialization, similar to how we handle the service name (and other labels that last for the entire pod lifetime).

See linkerd/linkerd2#13501 for the corresponding control plane change.

[cratelyn]

you've been clippy'ed 📎 🙀

Error: error: this function has too many arguments (8/7)
  --> linkerd/app/src/trace_collector/otel_collector.rs:21:1
   |
21 | / pub(super) fn create_collector<S>(
22 | |     addr: ControlAddr,
23 | |     hostname: Option<String>,
24 | |     pod_uid: Option<String>,
...  |
29 | |     legacy_metrics: metrics::Registry,
30 | | ) -> EnabledCollector
   | |_____________________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#too_many_arguments
   = note: `-D clippy::too-many-arguments` implied by `-D warnings`
   = help: to override `-D warnings` add `#[allow(clippy::too_many_arguments)]`

[cratelyn]

besides the note about clippy lints above, this looks like a good PR to me. this should be a nice improvement to our traces!

[codecov]

Codecov Report

Attention: Patch coverage is 7.14286% with 26 lines in your changes missing coverage. Please review.

Project coverage is 66.71%. Comparing base (96124bc) to head (89d0203).
Report is 688 commits behind head on main.

Files with missing lines	Patch %	Lines
linkerd/app/src/trace_collector/otel_collector.rs	0.00%	14 Missing ⚠️
linkerd/app/src/trace_collector.rs	0.00%	8 Missing ⚠️
linkerd/app/src/env.rs	33.33%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3483      +/-   ##
==========================================
- Coverage   67.68%   66.71%   -0.97%     
==========================================
  Files         332      388      +56     
  Lines       15158    18172    +3014     
==========================================
+ Hits        10259    12123    +1864     
- Misses       4899     6049    +1150     

Files with missing lines	Coverage Δ
linkerd/app/src/env.rs	52.71% <33.33%> (-6.68%)	⬇️
linkerd/app/src/trace_collector.rs	25.00% <0.00%> (ø)
linkerd/app/src/trace_collector/otel_collector.rs	0.00% <0.00%> (ø)

... and 175 files with indirect coverage changes

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 387197e...89d0203. Read the comment docs.

[olix0r]

We've generally been pretty adamant (and successful) about not leaking kubernetes concepts (pods, containers, uids, etc) into the proxy's codebase.

You may notice that we load a bunch of attributes from a file at starttime:

https://github.com/linkerd/linkerd2-proxy/pull/3483/files#diff-0ee25f0088036de1851c9f218f1abb2fd0c4abecefe846112c34c6533b2267ccR840-R845

is it possible to encode these attributes into this file so the proxy doesn't need special casing for them?