View Source PromEx.Plug (PromEx v1.11.0)

Use this plug in your Endpoint file to expose your metrics. The following options are supported by this plug:

• :prom_ex_module - The PromEx module whose metrics will be published through this particular plug
• :path - The path through which your metrics can be accessed (default is "/metrics")

If you need to have some sort of access control around your metrics endpoint, I would suggest looking at another library that I maintain called Unplug (https://hex.pm/packages/unplug). Using Unplug, you can skip over this plug if some sort of requirement is not fulfilled. For example, if you wanted to configure the metrics endpoint to only be accessible if the request has an Authorization header that matches a configured environment variable you could do something like so using Unplug:

defmodule MyApp.UnplugPredicates.SecureMetricsEndpoint do
  @behaviour Unplug.Predicate

  @impl true
  def call(conn, env_var) do
    expected_secret = System.fetch_env!(env_var)
    match?([^expected_secret], Plug.Conn.get_req_header(conn, "authorization"))
  end
end

Which can then be used in your endpoint.ex file like so:

plug Unplug,
  if: {MyApp.UnplugPredicates.SecureMetricsEndpoint, "PROMETHEUS_AUTH_SECRET"},
  do: {PromEx.Plug, prom_ex_module: MyApp.PromEx}

The reason that this functionality is not part of PromEx itself is that how you chose to configure the visibility of the metrics route is entirely up to the user and so it felt as though this plug would be over complicated by having to support application config, environment variables, etc. And given that Unplug exists for this purpose, it is the recommended tool for the job.