Plug.Telemetry (Plug v1.12.0) View Source
A plug to instrument the pipeline with
When plugged, the event prefix is a required option:
plug Plug.Telemetry, event_prefix: [:my, :plug]
In the example above, two events will be emitted:
[:my, :plug, :start]- emitted when the plug is invoked. The event carries the
system_timeas measurement. The metadata is the whole
:connkey and any leftover options given to the plug under
[:my, :plug, :stop]- emitted right before the request is sent. The event carries a single measurement,
:duration, which is the monotonic time difference between the stop and start events. It has the same metadata as the start event, except the connection has been updated.
Note this plug measures the time between its invocation until a response
is sent. The
:stop event is not guaranteed to be emitted in all error
cases, so this Plug cannot be used as a Telemetry span.
:duration measurements are presented in the
:native time unit.
You can read more about it in the docs for
defmodule InstrumentedPlug do use Plug.Router plug :match plug Plug.Telemetry, event_prefix: [:my, :plug] plug Plug.Parsers, parsers: [:urlencoded, :multipart] plug :dispatch get "/" do send_resp(conn, 200, "Hello, world!") end end
In this example, the stop event's
duration includes the time
it takes to parse the request, dispatch it to the correct handler,
and execute the handler. The events are not emitted for requests
not matching any handlers, since the plug is placed after the match plug.