## Previous Steps Before Starting

There are many cases where you want to perform some steps **before starting** your application.

For example, you might want to run **database migrations**.

But in most cases, you will want to perform these steps only **once**.

So, you will want to have a **single process** to perform those **previous steps**, before starting the application.

You can see it directly at: <a href="http://127.0.0.1:8000/openapi.json" class="external-link" target="_blank">http://127.0.0.1:8000/openapi.json</a>.

It will show a JSON starting with something like:

```JSON
{
    "openapi": "3.1.0",
    "info": {
        "title": "FastAPI",
        "version": "0.1.0"
    },
    "paths": {
        "/items/": {
            "get": {

!!! tip
    If you know perfectly how imports work, continue to the next section below.

A single dot `.`, like in:

```Python
from .dependencies import get_token_header
```

would mean:

* Starting in the same package that this module (the file `app/routers/items.py`) lives in (the directory `app/routers/`)...
* find the module `dependencies` (an imaginary file at `app/routers/dependencies.py`)...

## 구니콘을 유비콘 워커와 함께 실행하기

설치 후 구니콘 실행하기:

<div class="termy">

```console
$ gunicorn main:app --workers 4 --worker-class uvicorn.workers.UvicornWorker --bind 0.0.0.0:80

[19499] [INFO] Starting gunicorn 20.1.0
[19499] [INFO] Listening at: http://0.0.0.0:80 (19499)
[19499] [INFO] Using worker: uvicorn.workers.UvicornWorker
[19511] [INFO] Booting worker with pid: 19511
[19513] [INFO] Booting worker with pid: 19513

* In code blocks within the Markdown document, translate comments (`# a comment`), but leave the rest unchanged.

* Do not change anything enclosed in "``" (inline code).

* In lines starting with `===` or `!!!`, translate only the ` "... Text ..."` part. Leave the rest unchanged.

                            "items": {
                                "anyOf": [{"type": "string"}, {"type": "integer"}]
                            },
                        },
                        "msg": {"title": "Message", "type": "string"},
                        "type": {"title": "Error Type", "type": "string"},
                    },
                },
                "HTTPValidationError": {

                            "items": {
                                "anyOf": [{"type": "string"}, {"type": "integer"}]
                            },
                        },
                        "msg": {"title": "Message", "type": "string"},
                        "type": {"title": "Error Type", "type": "string"},
                    },
                },
                "HTTPValidationError": {

### Single Container

If you have a simple setup, with a **single container** that then starts multiple **worker processes** (or also just one process), then you could run those previous steps in the same container, right before starting the process with the app. The official Docker image supports this internally.

Dann können Sie Gunicorn ausführen mit:

<div class="termy">

```console
$ gunicorn main:app --workers 4 --worker-class uvicorn.workers.UvicornWorker --bind 0.0.0.0:80

[19499] [INFO] Starting gunicorn 20.1.0
[19499] [INFO] Listening at: http://0.0.0.0:80 (19499)
[19499] [INFO] Using worker: uvicorn.workers.UvicornWorker
[19511] [INFO] Booting worker with pid: 19511
[19513] [INFO] Booting worker with pid: 19513

### Flask REST frameworks

There are several Flask REST frameworks, but after investing the time and work into investigating them, I found that many are discontinued or abandoned, with several standing issues that made them unfit.

### <a href="https://marshmallow.readthedocs.io/en/stable/" class="external-link" target="_blank">Marshmallow</a>