> For the complete documentation index, see [llms.txt](https://openai.gitbook.io/code-cheatsheets/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://openai.gitbook.io/code-cheatsheets/all/elixir/phoenix.md).

# Phoenix

Web servers, API backends, and distributed messaging systems

Phoenix is ergonomic way to build web interfaces

* MVC framework, Ruby on Rails like
* Real-time messaging [Channels](https://hexdocs.pm/phoenix/channels.html) allowing pubsub and websockets out of the box
* Easy to test with high productivity & performance(**observer tool** can be used in prod, to find bottlenecks just see which process has a big message queue)
* Auto hot reloading, Postgres default
* **Presence** lets you replicate data across clients easily like which users are online

## Phoenix Layers

* [Endpoint](https://hexdocs.pm/phoenix/endpoint.html) - *lib/hello\_web/endpoint.ex*
  * the start and end of the request lifecycle
  * uses Plugs to do stuff like serve static files, log info, parse bodys => then routes to router
* [Router](https://hexdocs.pm/phoenix/routing.html) *- lib/hello\_web/router.ex*
  * parses incoming requests and dispatches them to the correct controller/action, passing parameters as needed
  * Pipelines - groups plugs that requests can go through
* [Controllers](https://hexdocs.pm/phoenix/controllers.html) - *lib/hello\_web/controllers/page\_controller.ex*
  * provide functions, called *actions*, to handle requests
  * actions:
    * prepare data then render views
    * perform redirects
* [Views](https://hexdocs.pm/phoenix/views.html) - *lib/hello\_web/views/page\_view\.ex*
  * controllers render templates, and views called implicitly
  * define helper functions, available in templates, to decorate data for presentation
* [Templates](https://hexdocs.pm/phoenix/templates.html) - *lib/hello\_web/templates/page/index.html.eex*.
  * files that will be served allowing dynamic data/code
  * nested in the app template found in app.html.eex
* [Channels](https://hexdocs.pm/phoenix/channels.html)
  * manage sockets for easy realtime communication
  * are analogous to controllers except that they allow bi-directional communication with persistent connections
* PubSub
  * underlies the channel layer and allows clients to subscribe to *topics*
  * abstracts the underlying pubsub adapter for third-party pubsub integration

## Other parts

### Plug

simple abstraction for dealing with different web servers

* Spec to create composable functions to build pipeline for requests to response
* Plug.Conn struct gives function for working with connections, session, body etc(both req and res object)
* Function Plugs -> recieves a connection and options and return connection
* Module plug is a module that must export init and call, extension of function

### Cowboy

most popular small, fast, modular HTTP server written in Erlang that underlies Phoenix

### Ecto

A DSL for writing queries and interacting with databases

### Contexts

Dedicated Modules that expose and group related functionality