wiki-manual-tracing

golang-wiki-tracing

This example illustrates a simple wiki application instrumented with the bare minimum necessary to utilize Honeycomb's tracing functionality, using the finished code from the "Writing Web Applications" Golang tutorial.

What We'll Do in This Example

We'll instrument a simple application for tracing by following a few general steps:

1. Set a top-level trace.trace_id at the origin of the request and set it on the request context. Generate a root span indicated by omitting a trace.parent_id field.
2. To represent a unit of work within a trace as a span, add code to generate a span ID and capture the start time. At the call site of the unit of work, pass down a new request context with the newly-generated span ID as the trace.parent_id. Upon work completion, send the span with a calculated duration_ms.
3. Rinse and repeat.

Note: Sound complicated? OpenTelemetry for Go handles all of this propagation magic for you :)

Usage

You can find your API key in your Environment Settings. If you do not have an API key yet, sign up for a free Honeycomb account.

Once you have your API key, run:

$ HONEYCOMB_API_KEY=foobarbaz go run wiki.go

And load http://localhost:8080/view/MyFirstWikiPage to create (then view) your first wiki page.

Methods within the simple wiki application have been instrumented with tracing-like calls, with context and tracing identifiers propagated via a context.Context.

Tips for Instrumenting Your Own Service

• For a given span (e.g. "loadPage"), remember that the span definition lives in its parent, and the instrumentation is around the call site of loadPage:

  loadPageID := fmt.Sprintf("%x", rand.Int63())
  start := time.Now()
  // Make sure to pass newContextWithParentID() -- with loadPageID as the
  // parent ID -- to loadPage in order to propagate span inheritance correctly
  loadPage(newContextWithParentID(r.Context(), loadPageID), title)
  sendSpan("loadPage", loadPageID, start, r.Context())
  

• If emitting Honeycomb events or structured logs, make sure that the start time gets used as the canonical timestamp, not the time at event emission.
• Remember, the root span should not have a trace.parent_id.
• Don't forget to add some metadata of your own! It's helpful to identify metadata in the surrounding code that might be interesting when debugging your application.
• Check out our OpenTelemetry for Go to get this context propagation for free!

A Note on Code Style

The purpose of this example is to illustrate the bare minimum necessary to propagate and set identifiers to enable tracing on an application for consumption by Honeycomb, illustrating the steps described in the top section of this README. We prioritized legibility over style and intentionally resisted refactoring that would sacrifice clarity. :)