これを実現するために、通常は**別のプログラム**を用意し、起動時にアプリケーションが実行されるようにします。そして多くの場合、他のコンポーネントやアプリケーション、例えばデータベースも実行されるようにします。

### 起動時に実行するツールの例

実行するツールの例をいくつか挙げます:

* Docker
* Kubernetes
* Docker Compose
* Swarm モードによる Docker
* Systemd
* Supervisor
* クラウドプロバイダーがサービスの一部として内部的に処理
* そのほか...

次の章で、より具体的な例を挙げていきます。

## 再起動

起動時にアプリケーションが実行されることを確認するのと同様に、失敗後にアプリケーションが**再起動**されることも確認したいと思われます。

### 我々は間違いを犯す

This means that instead of the normal process of your users sending requests to your API, it's **your API** (or your app) that could **send requests to their system** (to their API, their app).

This is normally called a **webhook**.

## Webhooks steps

The process normally is that **you define** in your code what is the message that you will send, the **body of the request**.

* the data from the client to be sent through the network
* the data sent by your program to be received by the client through the network
* the contents of a file in the disk to be read by the system and given to your program
* the contents your program gave to the system to be written to disk
* a remote API operation
* a database operation to finish
* a database query to return the results
* etc.

Linux containers run using the same Linux kernel of the host (machine, virtual machine, cloud server, etc). This just means that they are very lightweight (compared to full virtual machines emulating an entire operating system).

All built as reusable tools and components that are easy to integrate with your systems, data stores, relational and NoSQL databases, etc.

### Dependency Injection

FastAPI includes an extremely easy to use, but extremely powerful <abbr title='also known as "components", "resources", "services", "providers"'><strong>Dependency Injection</strong></abbr> system.

First you need to install `WebSockets`:

<div class="termy">

```console
$ pip install websockets

---> 100%
```

</div>

## WebSockets client

### In production

In your production system, you probably have a frontend created with a modern framework like React, Vue.js or Angular.

And to communicate using WebSockets with your backend you would probably use your frontend's utilities.

## Recap

You can use **Gunicorn** (or also Uvicorn) as a process manager with Uvicorn workers to take advantage of **multi-core CPUs**, to run **multiple processes in parallel**.

You could use these tools and ideas if you are setting up **your own deployment system** while taking care of the other deployment concepts yourself.

* dados do cliente para serem enviados através da rede
* dados enviados pelo seu programa para serem recebidos pelo clente através da rede
* conteúdo de um arquivo no disco pra ser lido pelo sistema e entregar ao seu programa
* conteúdo que seu programa deu ao sistema para ser escrito no disco
* uma operação remota API
* uma operação no banco de dados para finalizar
* uma solicitação no banco de dados esperando o retorno do resultado
* etc.

* `/items/{item_id}`

...as we intended.

* They will be marked with a list of tags that contain a single string `"items"`.
    * These "tags" are especially useful for the automatic interactive documentation systems (using OpenAPI).
* All of them will include the predefined `responses`.
* All these *path operations* will have the list of `dependencies` evaluated/executed before them.

* Declaración de **parámetros** en otros lugares diferentes cómo los: **headers**, **cookies**, **formularios** y **archivos**.
* Cómo agregar **requisitos de validación** cómo `maximum_length` o `regex`.
* Un sistema de **<abbr title="también conocido en inglés cómo: components, resources, providers, services, injectables">Dependency Injection</abbr>** poderoso y fácil de usar.