metrics: emit goodput track as a point attribute so the bandit evaluator can slice it

[reflog]

What

proxy.session.goodput now carries track as a point (datapoint) attribute keyed track, in addition to the existing proxy.track resource attribute.

Why

The goodput histogram (#674) tagged track only via the OTEL resource (semconv.ProxyTrackKey = "proxy.track"). SigNoz's metrics pipeline doesn't expose resource attributes as queryable metric labels, and the bandit experiment evaluator (lantern-cloud cmd/api/experiment/signoz.go) groups and filters goodput by the point attribute literally named track — the way lantern-box emits it.

Result: the evaluator's track IN [challenger, control] query matched sing-box/lantern-box tracks but never http-proxy tracks. Verified on prod:

• track = 'hysteria2-oci-free-vps' (sing-box) → goodput data
• track = 'blastoise-vps' (busy http-proxy incumbent, 21 routes, 24h) → 0; all http-proxy goodput sat in an untagged track="" bucket.

So every http-proxy challenger and http-proxy control arm read 0 goodput, and no http-proxy-backed bandit experiment could ever reach a verdict (it would hold until the 14-day max-gathering cutoff and retire inconclusive). This blocks the eng#3651 market-pivot experiments, whose challengers are http-proxy (tls_*) tracks.

Change

• instrument.SessionGoodput emits attribute.String("track", ins.track) as a point attribute alongside geo.country.iso_code and network.io.direction.
• track is threaded into defaultInstrument via NewDefault from the proxy's existing -track flag (p.Track).
• The resource still carries proxy.track for all other signals — unchanged.
• cloud.region is intentionally left a resource attribute: the evaluator's strata are (track, country) and a challenger is pinned to one DC, so region as a point attr would add cardinality with no decision value.

Tests

go build ./instrument/... + go vet clean; go test ./instrument/ -run TestSessionGoodput passes. Extended TestSessionGoodput to assert the track point attribute is present and equals the configured track. (Repo-wide go build ./... fails only on the pre-existing go-libutp CGO/compiler incompatibility, unrelated to this change.)

Rollout note

After merge: rebuild the http-proxy image and bump bandit_vps_http_proxy_default_short_tag in lantern-cloud so new VPS provisions emit track-tagged goodput. Existing experiment challengers were provisioned on the prior image; they'll pick up the new image on VPS autoreplace/recreate (or just let the current 4 retire and let post-rollout experiments be the measurable ones).

Summary by CodeRabbit

• New Features

  • Added tracking information to session goodput metrics, improving visibility into proxy activity reporting.
  • Metrics now include the proxy’s track label alongside existing location details.

• Tests

  • Updated metric tests to verify the new track label is included in emitted goodput data.

[coderabbitai]

Caution

Review failed

The pull request is closed.

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro Plus

Run ID: fff4fb2c-c856-40b4-b942-ce0de4861f25

📥 Commits

Reviewing files that changed from the base of the PR and between b0d6915 and ccf4407.

📒 Files selected for processing (4)

• http_proxy.go
• instrument/goodput_test.go
• instrument/instrument.go
• instrument/otelinstrument/otelinstrument.go

---

📝 Walkthrough

Walkthrough

NewDefault gains a track string parameter stored on defaultInstrument. SessionGoodput records this value as a track point attribute on the proxy.session.goodput histogram. ListenAndServe passes p.Track to NewDefault, and tests are updated to supply and assert the new attribute.

Changes

Track attribute in goodput instrumentation

Layer / File(s)	Summary
defaultInstrument track field and SessionGoodput attribute instrument/instrument.go, instrument/otelinstrument/otelinstrument.go	defaultInstrument gains a track field; NewDefault signature adds a track parameter and initializes the field; SessionGoodput includes track as a point attribute when recording the histogram. The otelinstrument comment clarifying which dimensions are point vs. resource attributes is updated accordingly.
Proxy wiring and test assertions http_proxy.go, instrument/goodput_test.go	ListenAndServe passes p.Track to NewDefault. Tests supply "test-track" to NewDefault and assert the histogram sample carries a track attribute equal to "test-track".

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Possibly related PRs

• getlantern/http-proxy#674: Directly related — introduces the proxy.session.goodput histogram that this PR extends with the track point attribute.

Poem

🐇 A track was lost, now found and stored,
Stitched into metrics, carefully poured.
The goodput histogram hops along,
With track as its label, precise and strong.
No attribute left behind! 🎉

✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch reflog/goodput-track-point-attr

---

_{Comment @coderabbitai help to get the list of available commands.}