The otel plugin is a Goa plugin that sets the http.route OpenTelemetry span attribute on generated HTTP handlers. This ensures the matched route pattern appears as a span attribute regardless of how otelhttp is wired into the application.

Import the plugin in the service design package with a blank identifier:

package design

import . "goa.design/goa/v3/dsl"
import _ "goa.design/plugins/v3/otel"

var _ = API("...

and generate as usual:

goa gen PACKAGE

The generated MountXxxHandler functions will set http.route on the active span before calling the handler:

mux.Handle("GET", "/users/{id}", func(w http.ResponseWriter, r *http.Request) {
    trace.SpanFromContext(r.Context()).SetAttributes(semconv.HTTPRoute("/users/{id}"))
    f(w, r)
})

As of Goa v3.25.0 the default muxer sets r.Pattern before middlewares run. If you register otelhttp as a mux middleware, it reads the route pattern automatically and this plugin is not necessary:

mux := goahttp.NewMuxer()
mux.Use(otelhttp.NewMiddleware("service"))

Use the plugin when you wrap the mux externally with otelhttp.NewHandler(mux, ...), since in that case r.Pattern is not yet available when otelhttp creates the span.