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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.

Table of Contents

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 to the end of our app.

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defmodule AppsignalPlugExample do
  use Plug.Router

  plug :match
  plug :dispatch

  get "/" do
    send_resp(conn, 200, "Welcome")
  end

  use Appsignal.Plug # <-- Add this
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

  1. use Appsignal.Instrumentation.Decorators to allow us to use AppSignal's instrumentation decorators
  2. Decorate the function we want to instrument with the transaction_event/0 decorator
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defmodule AppsignalPlugExample do
  use Plug.Router
  use Appsignal.Instrumentation.Decorators # <-- 1

  plug :match
  plug :dispatch

  get "/" do
    slow()
    send_resp(conn, 200, "Welcome")
  end

  @decorate transaction_event() # <-- 2
  defp slow do
    :timer.sleep(1000)
  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.