We have logs with correlation IDs. Do we still need tracing?

Correlation IDs let you collect one request's log lines, which is a big step, but you still reconstruct timing and causality by reading timestamps. Traces record the parent-child structure and precise durations directly, so an N+1 pattern or a serial call chain is visible as a shape instead of something you infer from log timestamps across machines with imperfect clocks.

How much overhead does tracing add to a request?

With sampling on, very little. Creating spans is nanoseconds of bookkeeping, and export happens off the request path in batches. Dapper measured negligible impact at 1 in 1024 sampling. The real costs are elsewhere: network and storage for span data, and collector infrastructure if you run tail-based sampling, which is why sampling strategy matters more than SDK overhead.

Is tracing worth it for a monolith?

Less urgent but still useful. A monolith calling a database, a cache, and three external APIs benefits from span timing on those calls, and in-process spans around major phases of a request show where time goes. The bigger payoff comes later: if you ever split the monolith, the propagation plumbing is already in place.

Observabilitychapter 3 of 4 · 4 lessons

Distributed Tracing

Follow a single request across every service to find where time was spent or failures occurred.

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Once a request touches ten services, the question of why it was slow stops having an easy answer. Each service's own dashboards look fine while the request as a whole takes four seconds.

Tracing is the signal built for exactly that gap, recording one request's path across every service with timing for each hop. Nobody adds it before they need it, which is unfortunate, because the day you need it is the day you cannot instrument ten services and wait for traffic.

Lessons

4 in this chapter

The Lost Request ProblemIn a microservice system, every team's graphs look fine while the user waits four seconds.2 min
Traces, Spans, and Context PropagationA trace is a tree of timed spans, glued together by IDs riding on every request.3 min
Sampling StrategiesYou cannot afford every trace, so choose between deciding early and cheap or late and smart.3 min
Tracing in PracticeOpenTelemetry to instrument once, a backend to search, and a short list of shapes to hunt for.3 min