A Local Feedback Loop With No Vendor

Why this matters

Agent instrumentation is fiddly enough that you want a fast loop, and waiting on a vendor account is the slowest possible start. Everything in this course can be developed against a local stack: a Jaeger container gives you a real waterfall for span topology, a Collector container lets you test redaction and sampling policies, and the console exporter lets you assert on span attributes in a unit test. Working locally is also better pedagogy, because you see the raw gen_ai.* attributes rather than a vendor's interpretation of them — which matters when you later need to know whether a missing field is your instrumentation or their rendering.

Demo

The compose file and the assertion pattern. The test is the part worth keeping: agent instrumentation is exactly the kind of thing that silently rots when someone refactors the loop, and a test on span structure catches it.

Try it yourself

1. Stand up the local stack and get one agent turn appearing as a trace in Jaeger.
2. Forget OTEL_TRACES_SAMPLER=always_on and note how confusing the missing trace is — then set it.
3. Write the span-topology test with a scripted model and confirm it passes.
4. Break context propagation in your agent loop and confirm the one-trace assertion catches it.
5. Add the prompt-leak assertion and check whether any attribute currently carries content you did not intend.

References

• Jaeger — Getting started
• OpenTelemetry Collector — Contrib image

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