Add cowboy_otel_h first to your cowboy stream handlers, it will pick up propagated spans to cowboy,
and surround the request with a span.
Also add cowboy_otel_middleware after your cowboy_router middlewares, it will attach the created
span from the stream process in the process executing middlewares and your cowboy handler, so subspans are connected.
ProtocolOpts = #{
stream_handlers => [cowboy_otel_h, cowboy_stream_h],
middlewares => [cowboy_router, cowboy_otel_middleware, cowboy_handler],
...
}Goal is to follow https://opentelemetry.io/docs/specs/semconv/http/http-spans/
If sampling needs are simple then cowboy_otel_sampler can be useful to exclude
a span called <<"GET /metrics">> with configuration:
{opentelemetry, [
{sampler, {parent_based, #{root => {cowboy_otel_sampler, [<<"GET /metrics">>]}}}}
]}
This sampler will exclude spans of kind server whose name is in the provided list.