Intercept B3 headers and join a sampled trace, or run a sampler to determine whether to start a new trace.

If starting a trace, a ‘server receive’ (sr) annotation will be added to the root span, as well as details about the request. A call-back is installed to finish the trace at the end of the request, adding additional http.status_code and a ‘server send’ (ss) annotations.

plug Tapper.Plug.Trace, sampler: Tapper.Plug.Sampler.Simple, percent: 25

or e.g.

plug Tapper.Plug.Trace, sampler: fn(conn, _config) -> String.starts_with?(conn.request_path, ["/foo", "/bar"]) end

Options

• sampler - name of module with sample?/2, or a fun with arity 2, to call to determine whether to sample a request; see Tapper.Plug.Sampler.
• debug - if set to true all requests, joined or started, will be sampled.
• tapper - keyword list passed on to Tapper.start/1 or Tapper.join/6 (useful for testing/debugging, but use with caution since overrides options set by this module).

All options, including custom ones, will be passed to the sampler function (as a map), which means it can be configured here too.

Annotations

Tapper.Plug sets the following annotations:

• sr - server receive on starting or joining a trace.
• ca - client address, from conn.remote_ip.
• http.host, http.method, http.path - from corresponding Plug.Conn fields.
• ss - server send when finishing a trace.