How to include ranch in a supervision tree

I have the following supervisor children:

       [
          %{
            id: :ranch_sup,
            start: {:ranch_sup, :start_link, []},
            restart: :permanent,
            shutdown: 5000,
            type: :supervisor
          },
          :ranch.child_spec(Server, :ranch_tcp, [port: 6666], Server, [])
        ]

and in mix.exs:

  # Run "mix help compile.app" to learn about applications.
  def application do
    [
      extra_applications: [:logger],
      included_applications: [:ranch],
      mod: {Server.Application, []}
    ]
  end

  # Run "mix help deps" to learn about dependencies.
  defp deps do
    [
      {:ranch, "~> 1.7", runtime: false}
    ]
  end

The problem is that elixir makes :ranch start its supervisor automatically, I guess … which causes

18:00:50.418 [info]  Application server exited: Server.Application.start(:normal, []) returned an error: shutdown: failed to start child: :ranch_sup
    ** (EXIT) already started: #PID<0.895.0>
{"Kernel pid terminated",application_controller,"{application_start_failure,server,{{shutdown,{failed_to_start_child,ranch_sup,{already_started,<0.895.0>}}},{'Elixir.Server.Application',start,[normal,[]]}}}"}
Kernel pid terminated (application_controller) ({application_start_failure,server,{{shutdown,{failed_to_start_child,ranch_sup,{already_started,<0.895.0>}}},{'Elixir.Server.Application',start,

Crash dump is being written to: erl_crash.dump...done
1 Like

So the question is, how do I include :ranch in a supervision tree, that is, include the application (so that it gets into a release) while not starting it?

I guess I can remove ranch_sup from the children list and only keep the listener there, but I remember that caused problems with app shutdown …

Ranch is an application. That means it is responsible for maintaining its own, independent, supervision tree. It does not seem proper for you to try and start that applications tree within your own application’s tree.

Can you elaborate more on the problem you are trying to solve (not the solution you are pursuing to solve it?)

That means it is responsible for maintaining its own, independent, supervision tree. It does not seem proper for you to try and start that applications tree within your own application’s tree.

Not quite: https://ninenines.eu/docs/en/ranch/1.7/guide/embedded/

Can you elaborate more on the problem you are trying to solve (not the solution you are pursuing to solve it?)

The problem is I want to be able to start and stop ranch instances during tests, and I failed to do so with it being started as an app, and wanted to try start_supervised! and friends.


This “XY problem” reply seems to be getting more and more popular on this forum :slight_smile:

I’d still want to know how to achieve what I want in the OP, it sometimes comes in handy, I remember I had a similar problem with :pigeon recently where it was only started in :prod, but still had to be included in :dev to export dialyzer types.

The setup you describe here seems to work for me out of the box as it seems…

Have you perhaps an Application.ensure_all_started(:ranch) somewhere, as it is suggested all over the docs?