phoenix-api-channels

Phoenix APIs, Channels, and Presence (Elixir/BEAM)

Phoenix excels at REST/JSON APIs and WebSocket Channels with minimal boilerplate, leveraging the BEAM for fault tolerance, lightweight processes, and supervised PubSub/Presence.

Core pillars

• Controllers for JSON APIs with plugs, pipelines, and versioning.
• Contexts own data (Ecto schemas + queries) and expose a narrow API to controllers/channels.
• Channels + PubSub for fan-out real-time updates; Presence for tracking users/devices.
• Auth via plugs (session/cookie for browser, token/Bearer for APIs), with signed params.

---

Project Setup

mix phx.new my_api --no-html --no-live
cd my_api
mix deps.get
mix ecto.create
mix phx.server

Key files:

• lib/my_api_web/endpoint.ex — plugs, sockets, instrumentation
• lib/my_api_web/router.ex — pipelines, scopes, versioning, sockets
• lib/my_api_web/controllers/* — REST/JSON controllers
• lib/my_api/* — contexts + Ecto schemas (ownership of data logic)
• lib/my_api_web/channels/* — Channel modules

---

Routing and Pipelines

Separate browser vs API pipelines; version APIs with scopes.

defmodule MyApiWeb.Router do
  use MyApiWeb, :router

  pipeline :api do
    plug :accepts, ["json"]
    plug :fetch_session
    plug :protect_from_forgery
    plug MyApiWeb.Plugs.RequireAuth
  end

  scope "/api", MyApiWeb do
    pipe_through :api

    scope "/v1", V1, as: :v1 do
      resources "/users", UserController, except: [:new, :edit]
      post "/sessions", SessionController, :create
    end
  end

  socket "/socket", MyApiWeb.UserSocket,
    websocket: [connect_info: [:peer_data, :x_headers]],
    longpoll: false
end

Tips

• Keep pipelines short; push auth/guards into plugs.
• Expose socket "/socket" for Channels; restrict transports as needed.

---

Controllers and Plugs

Controllers stay thin; contexts own the logic.

defmodule MyApiWeb.V1.UserController do
  use MyApiWeb, :controller
  alias MyApi.Accounts

  action_fallback MyApiWeb.FallbackController

  def index(conn, _params) do
    users = Accounts.list_users()
    render(conn, :index, users: users)
  end

  def create(conn, params) do
    with {:ok, user} <- Accounts.register_user(params) do
      conn
      |> put_status(:created)
      |> put_resp_header("location", ~p\"/api/v1/users/#{user.id}\")
      |> render(:show, user: user)
    end
  end
end