Scout Absinthe (GraphQL) Instrumentation

scout_apm_absinthe_plug.ex

defmodule ScoutApm.Absinthe.Plug do
  alias ScoutApm.Internal.Layer

  def init(default), do: default

  def call(conn, _default) do
    ScoutApm.TrackedRequest.start_layer("Controller", action_name(conn))

    conn
    |> Plug.Conn.register_before_send(&before_send/1)
  end
  def before_send(conn) do
    full_name = action_name(conn)
    uri = "#{conn.request_path}"
    ScoutApm.TrackedRequest.stop_layer(fn layer ->
        layer
        |> Layer.update_name(full_name)
        |> Layer.update_uri(uri)
      end
    )
    conn
  end

  # Takes a connection, extracts the phoenix controller & action, then manipulates & cleans it up.
  # Returns a string like "PageController#index"
  defp action_name(conn) do
    action_name = conn.params["operationName"]
    "GraphQL##{action_name}"
  end
end

In case anyone is interested, the plug shown is dependent on the operationName being set for the GraphQL queries. For the project I'm working on, we don't name the queries/mutations we send to Absinthe, but limit each query/mutation to a single field per request. In this case, using the code above results in all GraphQL requests being labelled "GraphQL" in Scout. I needed a way to extract the first field so that queries/mutations like the one below show up as "GraphQL#firstField" in Scout.

query {
  firstField(id: 1) {
    id
  }
}

Here's what I arrived at: https://gist.github.com/pgrunwald/6dd1d9132855b0372785e75df4a26669

Updated gist from @percygrunwald: https://gist.github.com/percygrunwald/6dd1d9132855b0372785e75df4a26669

Also, add this Plug to the Router pipeline as follows:

defmodule MyAppWeb.Router do
  use MyAppWeb, :router

  pipeline :api do
    plug :accepts, ["json"]
    plug MyAppWeb.Context
    # add here
    plug ScoutApm.Absinthe.Plug
  end
  ....