Tracing

Every route in this series goes around the Go runtime: rewrite the source at build time, inject something at process start, or watch from the kernel, because Go gives us no agent API to plug into. This time we ask the runtime what it could hand us. The honest summary for 2026: one long-awaited feature shipped, two open proposals document gaps that have caused real production problems for years, and two experiments of mine are aspirations, not proposals. ...

We’re going to follow one request, GET /orders/42, and ask what “propagation” means at each hop. Three different jobs hide behind that word, the tools in this series do different ones, and the request’s own data falls into the gaps between them. The cheapest way to see a gap is a short Go program. This is a companion to the How to Instrument Go Without Changing a Single Line of Code series, between Part 4 and Part 5. The series accompanies my GopherCon UK talk. Part 1 showed tools hacking a field into g. Here we look at what that field holds, what it can’t, and who does the rest. ...