Emit OpenTelemetry spans over OTLP

[ross]

Adds distributed tracing to simone. Each gunicorn worker sets up an OpenTelemetry TracerProvider and exports spans over OTLP/HTTP to whatever OTEL_EXPORTER_OTLP_ENDPOINT names — Grafana Tempo, in the compose stack this runs in.

The point is a request showing up as one trace across tiers. nginx now mints a trace id per request and forwards it as a W3C traceparent; the default propagator picks it up here with no code of our own, so simone's request span becomes a child of the span nginx's access log line produces, instead of the two being unrelated halves.

Why post_fork

Not import time, and not the opentelemetry-instrument CLI wrapper. BatchSpanProcessor owns a background export thread, and a thread does not survive fork() — only the forking thread's state does. A provider built in the gunicorn master would leave the worker holding a processor whose export thread only ever existed in the parent, silently exporting nothing. post_fork runs inside each freshly forked worker, before it imports simone.wsgi.

This agrees with the reason already documented at the top of gunicorn.conf.py for not running with --preload; nothing about the Cron-thread hazard changes.

The DJANGO_SETTINGS_MODULE move

DjangoInstrumentor().instrument() reads Django settings itself (to find MIDDLEWARE), and gunicorn runs post_fork before the worker imports simone.wsgi — where the setdefault used to live. Without moving it to module scope, Django's LazySettings configures itself from global_settings first, and since it only consults the env var the first time it's forced to configure, wsgi.py's later get_wsgi_application() never loads simone.settings at all. Every request then 500s with AttributeError on ROOT_URLCONF. Hit this directly while testing, not by inference.

Notes

• The hook is a no-op when OTEL_EXPORTER_OTLP_ENDPOINT is unset, so script/run and the dev docker-compose.yml need no collector listening.
• requirements.txt is additive only. Regenerating it with script/update-requirements also re-resolved a dozen unrelated pins (django-debug-toolbar 7→8, gunicorn 26.0→26.2, …); those were dropped so this diff is just the new packages. Worth a separate maintenance pass.
• wrapt resolves to 2.4.1rc1 — a release candidate, pulled in by opentelemetry-instrumentation. It's what resolves across the 3.10–3.14 range this project supports, but flagging it rather than burying it.

Verified

Ran the hook directly against a local OTLP sink: provider installed with service.name=simone/service.namespace=xormedia, Django reported instrumented, an inbound traceparent correctly extracted, and one real application/x-protobuf POST to /v1/traces carrying a span whose trace id and parent span id match the inbound header. Existing test suite (30 tests) and script/lint/script/format pass.

🤖 Generated with Claude Code

https://claude.ai/code/session_013LW5eUDxvLcyY9JKbfqMux