View Source Plug.Telemetry (Plug v1.14.0)
A plug to instrument the pipeline with :telemetry
events.
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 thesystem_time
as measurement. The metadata is the wholePlug.Conn
under the:conn
key and any leftover options given to the plug under:options
.[: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.
time-unit
Time unit
The :duration
measurements are presented in the :native
time unit.
You can read more about it in the docs for System.convert_time_unit/3
.
example
Example
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.