blset

Pubsub in a phoenix app under umbrella

When creating a new project with

mix phx.new proj --umbrella

the phoenix_pubsub dependency is placed in the mix.exs of the proj app and not under the proj_web app.

but that seems against app isolation. since the proj app, in the idea, should have no dependency on phoenix nor any web consideration.

more over when manually placing the phoenix pub_sub in the proj_web mix.exs and adjusting the config of the umbrella config, it does not work with message

unknown registry: ProjWeb.PubSub

how to make i work with phoenix_pubsub under the web app ?

17 comments

/phoenix #umbrella #phoenix_pubsub

16 7218 17

2022-09-08 19:48:48 UTC

Marked As Solved

LostKobrakai

Here’s the place it’s started for a single project phoenix app:

github.com/phoenixframework/phoenix

installer/templates/phx_single/lib/app_name/application.ex

v1.5


      
          
          use Application
          
          def start(_type, _args) do
            children = [<%= if ecto do %>
              # Start the Ecto repository
              <%= app_module %>.Repo,<% end %>
              # Start the Telemetry supervisor
              <%= web_namespace %>.Telemetry,
              # Start the PubSub system
              {Phoenix.PubSub, name: <%= app_module %>.PubSub},
              # Start the Endpoint (http/https)
              <%= endpoint_module %>
              # Start a worker by calling: <%= app_module %>.Worker.start_link(arg)
              # {<%= app_module %>.Worker, arg}
            ]
          
            # See https://hexdocs.pm/elixir/Supervisor.html
            # for other strategies and supported options
            opts = [strategy: :one_for_one, name: <%= app_module %>.Supervisor]
            Supervisor.start_link(children, opts)

And here for the umbrella version:

github.com/phoenixframework/phoenix

installer/templates/phx_umbrella/apps/app_name/lib/app_name/application.ex

v1.5


      
            # for more information on OTP Applications
            @moduledoc false
          
            use Application
          
            def start(_type, _args) do
              children = [<%= if ecto do %>
                # Start the Ecto repository
                <%= app_module %>.Repo,<% end %>
                # Start the PubSub system
                {Phoenix.PubSub, name: <%= app_module %>.PubSub}
                # Start a worker by calling: <%= app_module %>.Worker.start_link(arg)
                # {<%= app_module %>.Worker, arg}
              ]
          
              Supervisor.start_link(children, strategy: :one_for_one, name: <%= app_module %>.Supervisor)
            end
          end

Post #8

Also Liked

josefrichter

I would like to add this here for future reference:

I ran into this problem while going thru Programming Phoenix 1.4 book, Chapter 11, section Extracting Rumbl and RumblWeb, page 238 very bottom.

The error encountered is this (adding to be google-able):

** (Mix) Could not start application rumbl_web: RumblWeb.Application.start(:normal, []) returned an error: shutdown: failed to start child: RumblWeb.Presence
    ** (EXIT) shutdown: failed to start child: Phoenix.Presence.Tracker
        ** (EXIT) shutdown: failed to start child: RumblWeb.Presence_shard0
            ** (EXIT) an exception was raised:
                ** (ArgumentError) unknown registry: RumblWeb.PubSub
...

The exact solution based on this thread seems to be editing /rumbl_umbrella/apps/rumbl/lib/rumbl/application.ex so that the children there are:

children = [
      Rumbl.Repo,
      {Phoenix.PubSub, name: Rumbl.PubSub}, # added missing piece
    ]

The file /rumbl_umbrella/config/config.exs says that the pub_sub server for rumbl_web is this

config :rumbl_web, RumblWeb.Endpoint,
  ...
  pubsub_server: Rumbl.PubSub,
  ...

so then I also changed /rumbl_umbrella/apps/rumbl_web/lib/rumbl_web/channels/presence.ex so that it starts with

use Phoenix.Presence,
    otp_app: :rumbl_web,
    pubsub_server: Rumbl.PubSub

Upon all these changes it seems to work (despite having some “connection refused” messages in console). Long story short, seems like one needs Rumbl.PubSub consistently everywhere.

Hope this helps somebody.

Post #14

NobbZ

PubSub, even though used by the channels, is not a web concern. It is to send (publish) messages to a couple of subscribers, in a way that the publisher does not need to know the subscribers, while also the subscribers do not need to know the publisher(s) in advance.

It can be used for a lot more things than just “web”.

Post #2

Thomas-Sciaroni

In addition to what Jose mentioned, I also needed to update the children in
./rumbl_umbrella/apps/rumbl_web/lib/rumbl_web/application.ex
by adding

children = [
  ...
  RumbWeb.Presence
]

otherwise I was getting the error:

[error] GenServer #PID<{PID}> terminating
** (ArgumentError) argument error
(stdlib 3.13) :ets.lookup(RumblWeb.Presence, :pool_size)
    (phoenix_pubsub 2.0.0) lib/phoenix/tracker.ex:311: Phoenix.Tracker.pool_size/1
    (phoenix_pubsub 2.0.0) lib/phoenix/tracker.ex:240: Phoenix.Tracker.list/2
    (phoenix 1.5.6) lib/phoenix/presence.ex:401: Phoenix.Presence.list/2
    (rumbl_web 0.1.0) lib/rumbl_web/channels/video_channel.ex:40: RumblWeb.VideoChannel.handle_info/2
    (phoenix 1.5.6) lib/phoenix/channel/server.ex:344: Phoenix.Channel.Server.handle_info/2
    (stdlib 3.13) gen_server.erl:680: :gen_server.try_dispatch/4
    (stdlib 3.13) gen_server.erl:756: :gen_server.handle_msg/6
    (stdlib 3.13) proc_lib.erl:226: :proc_lib.init_p_do_apply/3
Last message: :after_join
State: %Phoenix.Socket{assigns: %{user_id: ...
...}

Post #15