Defines a Phoenix endpoint.

The endpoint is the boundary where all requests to your web application start. It is also the interface your application provides to the underlying web servers.

Overall, an endpoint has three responsibilities:

• to provide a wrapper for starting and stopping the endpoint as part of a supervision tree

• to define an initial plug pipeline for requests to pass through

• to host web specific configuration for your application

Endpoints

An endpoint is simply a module defined with the help of Phoenix.Endpoint. If you have used the mix phx.new generator, an endpoint was automatically generated as part of your application:

defmodule YourApp.Endpoint do
  use Phoenix.Endpoint, otp_app: :your_app

  # plug ...
  # plug ...

  plug YourApp.Router
end

Endpoints must be explicitly started as part of your application supervision tree. Endpoints are added by default to the supervision tree in generated applications. Endpoints can be added to the supervision tree as follows:

children = [
  YourApp.Endpoint
]

Endpoint configuration

All endpoints are configured in your application environment. For example:

config :your_app, YourApp.Endpoint,
  secret_key_base: "kjoy3o1zeidquwy1398juxzldjlksahdk3"

Endpoint configuration is split into two categories. Compile-time configuration means the configuration is read during compilation and changing it at runtime has no effect. The compile-time configuration is mostly related to error handling.

Runtime configuration, instead, is accessed during or after your application is started and can be read through the config/2 function:

YourApp.Endpoint.config(:port)
YourApp.Endpoint.config(:some_config, :default_value)

Dynamic configuration

For dynamically configuring the endpoint, such as loading data from environment variables or configuration files, Phoenix invokes the init/2 callback on the endpoint, passing a :supervisor atom as first argument and the endpoint configuration as second.

All of Phoenix configuration, except the Compile-time configuration below can be set dynamically from the init/2 callback.

Compile-time configuration

• :code_reloader - when true, enables code reloading functionality. For the list of code reloader configuration options see Phoenix.CodeReloader.reload!/1

• :debug_errors - when true, uses Plug.Debugger functionality for debugging failures in the application. Recommended to be set to true only in development as it allows listing of the application source code during debugging. Defaults to false

• :render_errors - responsible for rendering templates whenever there is a failure in the application. For example, if the application crashes with a 500 error during a HTML request, render("500.html", assigns) will be called in the view given to :render_errors. Defaults to:

  [view: MyApp.ErrorView, accepts: ~w(html), layout: false]

  The default format is used when none is set in the connection

Runtime configuration

• :cache_static_manifest - a path to a json manifest file that contains static files and their digested version. This is typically set to "priv/static/cache_manifest.json" which is the file automatically generated by mix phx.digest. It can be either: a string containing a file system path or a tuple containing the application name and the path within that application.

• :check_origin - configure transports to check origin header or not. May be false, true, a list of hosts that are allowed, or a function provided as MFA tuple. Hosts also support wildcards.

  For example, using a list of hosts:

  check_origin: ["//phoenixframework.org", "//*.example.com"]

  or a custom MFA function:

  check_origin: {MyAppWeb.Auth, :my_check_origin?, []}

  The MFA is invoked with the request %URI{} as the first argument, followed by arguments in the MFA list

  Defaults to true.

• :http - the configuration for the HTTP server. Currently uses Cowboy and accepts all options as defined by Plug.Cowboy. Defaults to false

• :https - the configuration for the HTTPS server. Currently uses Cowboy and accepts all options as defined by Plug.Cowboy. Defaults to false

• :force_ssl - ensures no data is ever sent via HTTP, always redirecting to HTTPS. It expects a list of options which are forwarded to Plug.SSL. By default it sets the "strict-transport-security" header in HTTPS requests, forcing browsers to always use HTTPS. If an unsafe request (HTTP) is sent, it redirects to the HTTPS version using the :host specified in the :url configuration. To dynamically redirect to the host of the current request, set :host in the :force_ssl configuration to nil

• :secret_key_base - a secret key used as a base to generate secrets for encrypting and signing data. For example, cookies and tokens are signed by default, but they may also be encrypted if desired. Defaults to nil as it must be set per application

• :server - when true, starts the web server when the endpoint supervision tree starts. Defaults to false. The mix phx.server task automatically sets this to true

• :url - configuration for generating URLs throughout the app. Accepts the :host, :scheme, :path and :port options. All keys except :path can be changed at runtime. Defaults to:

  [host: "localhost", path: "/"]

  The :port option requires either an integer, string, or {:system, "ENV_VAR"}. When given a tuple like {:system, "PORT"}, the port will be referenced from System.get_env("PORT") at runtime as a workaround for releases where environment specific information is loaded only at compile-time.

  The :host option requires a string or {:system, "ENV_VAR"}. Similar to :port, when given a tuple like {:system, "HOST"}, the host will be referenced from System.get_env("HOST") at runtime.

  The :scheme option accepts "http" and "https" values. Default value is infered from top level :http or :https option. It is useful when hosting Phoenix behind a load balancer or reverse proxy and terminating SSL there.

  The :path option can be used to override root path. Useful when hosting Phoenix behind a reverse proxy with URL rewrite rules

• :static_url - configuration for generating URLs for static files. It will fallback to url if no option is provided. Accepts the same options as url

• :watchers - a set of watchers to run alongside your server. It expects a list of tuples containing the executable and its arguments. Watchers are guaranteed to run in the application directory, but only when the server is enabled. For example, the watcher below will run the "watch" mode of the webpack build tool when the server starts. You can configure it to whatever build tool or command you want:

  [node: ["node_modules/webpack/bin/webpack.js", "--mode", "development",
      "--watch-stdin"]]

  The :cd option can be used on a watcher to override the folder from which the watcher will run. By default this will be the project's root: File.cwd!()

  [node: ["node_modules/webpack/bin/webpack.js", "--mode", "development",
      "--watch-stdin"], cd: "my_frontend"]

• :live_reload - configuration for the live reload option. Configuration requires a :patterns option which should be a list of file patterns to watch. When these files change, it will trigger a reload. If you are using a tool like pow in development, you may need to set the :url option appropriately.

  live_reload: [
    url: "ws://localhost:4000",
    patterns: [
      ~r{priv/static/.*(js|css|png|jpeg|jpg|gif)$},
      ~r{web/views/.*(ex)$},
      ~r{web/templates/.*(eex)$}
    ]
  ]

• :pubsub - configuration for this endpoint's pubsub adapter. Configuration either requires a :name of the registered pubsub server or a :name and :adapter pair. The pubsub name and adapter are compile time configuration, while the remaining options are runtime. The given adapter and name pair will be started as part of the supervision tree. If no adapter is specified, the pubsub system will work by sending events and subscribing to the given name. Defaults to:

  [adapter: Phoenix.PubSub.PG2, name: MyApp.PubSub]

  It also supports custom adapter configuration:

  [name: :my_pubsub, adapter: Phoenix.PubSub.Redis,
   host: "192.168.100.1"]

Endpoint API

In the previous section, we have used the config/2 function that is automatically generated in your endpoint. Here's a list of all the functions that are automatically defined in your endpoint:

• for handling paths and URLs: struct_url/0, url/0, path/1, static_url/0,static_path/1, and static_integrity/1
• for handling channel subscriptions: subscribe/2 and unsubscribe/1
• for broadcasting to channels: broadcast/3, broadcast!/3, broadcast_from/4, and broadcast_from!/4
• for configuration: start_link/0, config/2, and config_change/2
• as required by the Plug behaviour: Plug.init/1 and Plug.call/2

Instrumentation

Phoenix uses the :telemetry library for instrumentation. The following events are published by Phoenix with the following measurements and metadata:

• [:phoenix, :endpoint, :start] - dispatched by Plug.Telemetry in your endpoint at the beginning of every request.

  • Measurement: %{time: System.monotonic_time}
  • Metadata: %{conn: Plug.Conn.t}

• [:phoenix, :endpoint, :stop] - dispatched by Plug.Telemetry in your endpoint whenever the response is sent

  • Measurement: %{duration: native_time}
  • Metadata: %{conn: Plug.Conn.t}

• [:phoenix, :router_dispatch, :start] - dispatched by Phoenix.Router before dispatching to a matched route

  • Measurement: %{time: System.monotonic_time}
  • Metadata: %{conn: Plug.Conn.t, route: binary, plug: module, plug_opts: term, path_params: map, pipe_through: [atom]}

• [:phoenix, :router_dispatch, :stop] - dispatched by Phoenix.Router after successfully dispatching to a matched route

  • Measurement: %{duration: native_time}
  • Metadata: %{conn: Plug.Conn.t, route: binary, plug: module, plug_opts: term, path_params: map, pipe_through: [atom]}

• [:phoenix, :error_rendered] - dispatched at the end of an error view being rendered

  • Measurement: %{duration: native_time}
  • Metadata: %{status: Plug.Conn.status, kind: Exception.kind, reason: term, stacktrace: Exception.stacktrace}

• [:phoenix, :socket_connected] - dispatched at the end of a socket connection

  • Measurement: %{duration: native_time}
  • Metadata: %{endpoint: atom, transport: atom, params: term, connect_info: map, vsn: binary, user_socket: atom, result: :ok | :error, serializer: atom}

• [:phoenix, :channel_joined] - dispatched at the end of a channel join

  • Measurement: %{duration: native_time}
  • Metadata: %{params: term, socket: Phoenix.Socket.t}

• [:phoenix, :channel_handled_in] - dispatched at the end of a channel handle in

  • Measurement: %{duration: native_time}
  • Metadata: %{event: binary, params: term, socket: Phoenix.Socket.t}