Integrating AppSignal into Plug

Note: Support for custom namespaces was added in version 1.3.0 of the AppSignal for Elixir package.

The AppSignal for Elixir package integrates with Plug. To set up the integration, please follow our installation guide.

This page describes how to set up AppSignal in a Plug application, and how to add instrumentation for events within requests. For more information about custom instrumentation, read the Elixir instrumentation documentation.

More information can be found in the AppSignal Hex package documentation.


The AppSignal instrumentation for Plug is part of a separate package, which depends on the primary appsignal package. Add the appsignal_plug package to your mix.exs file.

# mix.exs defmodule AppsignalPlugExample.MixProject do # ... defp deps do [ {:plug, "~> 1.0"}, # Or plug_cowboy ~> 2.0 {:appsignal_plug, "~> 2.0"} # ... ] end end

If you're already using our appsignal_phoenix package, it's not necessary to add the appsignal_plug package as it's already a dependency of the appsignal_phoenix package. See also our Phoenix integration guide.

Incoming HTTP requests

We'll start out with a small Plug app that accepts GET requests to / and returns a welcome message. To start logging HTTP requests in this app, we'll use the Appsignal.Plug module.

defmodule AppsignalPlugExample do use Plug.Router use Appsignal.Plug # <- Add this plug :match plug :dispatch get "/" do send_resp(conn, 200, "Welcome") end end

This will create a transaction for every HTTP request which is performed on the endpoint.

Custom instrumentation

Although Appsignal.Plug will start transactions for you, it won't instrument events in your app just yet. To do that, we need to add some custom instrumentation.

This example app looks like the one we used before, but it has a slow function (aptly named slow/0) we'd like to add instrumentation for. To do that, we need to use the Appsignal.instrument/2-3 helper in our called function:

defmodule AppsignalPlugExample do use Plug.Router plug :match plug :dispatch get "/" do slow() send_resp(conn, 200, "Welcome") end defp slow do Appsignal.instrument("slow", fn -> :timer.sleep(1000) end) end use Appsignal.Plug end

This will add an event for the slow/0 function to the current transaction whenever it's called. For more information about custom instrumentation, read the Elixir instrumentation documentation.

Instrumentation for included Plugs

Exceptions in included Plugs are automatically caught by AppSignal, but performance samples need to be set up manually using the custom instrumentation helpers or decorators.

Plug instrumentation with decorators

To add instrumentation to Plugs, use the Appsignal.instrument/2 function:

defmodule SlowPlugWithDecorators do import Plug.Conn def init(opts), do: opts def call(conn, _) do Appsignal.instrument("SlowPlugWithDecorators", fn -> :timer.sleep(1000) conn end) end end