> ## Documentation Index
> Fetch the complete documentation index at: https://docs.fly.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Run a FastAPI app

Getting an application running on Fly.io is essentially working out how to package it as a deployable image. Once packaged, it can be deployed to the Fly.io platform.

In this guide we’ll learn how to deploy a [FastAPI](https://fastapi.tiangolo.com/) application on Fly.io.

FastAPI is a modern, fast (high-performance), web framework for building APIs with Python based on standard Python type hints.

Deploying a FastAPI app on Fly.io is... well it's fast! You can be up and running in less than a minute.

## *Speedrun*

First, [install flyctl](/flyctl/install), the Fly.io CLI, and [sign up to Fly.io](/getting-started/sign-up-sign-in#first-time-or-no-fly-account-sign-up-for-fly) if you haven't already.

The fastest way to get a basic Fast Api server on Fly.io is to use our FastAPI template:

```sh theme={null}
git clone git@github.com:fly-apps/hello-fastapi.git fastapi-app
cd fastapi-app
fly launch --generate-name
```

## *Deploy a FastAPI app from scratch*

For managing our project, we use [Poetry](https://python-poetry.org/).
For more information on the initial setup with poetry, refer to [setting up a python environment](/python/the-basics/initial-setup).

We can initialize a new project like so:

```bash theme={null}
poetry new fastapi-app
cd fastapi-app
```

<Info>
  If you're using Poetry 2.0+ (the default when installed via `pipx`), the `poetry shell` command is no longer built in. Use `poetry run` to run commands (e.g., `poetry run python main.py`), or activate the environment with `poetry env activate`. See the [initial setup guide](/python/the-basics/initial-setup) for more details.
</Info>

Then we have to add the FastAPI dependency:

```bash theme={null}
poetry add "fastapi[standard]"
```

Now, let's create a simple FastAPI app in `main.py`:

```python theme={null}
from fastapi import FastAPI

app = FastAPI()

@app.get("/")
async def hello_fly():
    return 'hello from fly.io'

```

We can then serve the development version of the app using the `fastapi` cli tool:

```bash theme={null}
fastapi dev
```

This will display a 'hello from fly.io!' message when you visit the root URL.
With the development environment we also get cool features like hot-reloading.

To run in production mode, we can amend the command:

```bash theme={null}
fastapi run
```

<Info>
  The `fastapi` assumes your app is stored in `main.py` or `app.py` - if this is not the case, you must specify that when running the app:

  `fastapi run hello/entrypoint.py`
</Info>

And with that you can deploy the app!

<CodeGroup>
  ```bash cmd theme={null}
  fly launch
  ```

  ```output output theme={null}
  Scanning source code
  Detected a FastAPI app
  Warning: This organization has no payment method, turning off high availability
  Creating app in [redacted]/[app-name]
  We're about to launch your app on Fly.io. Here's what you're getting:

  Organization: Your Name              (fly launch defaults to the personal org)
  Name:         [app-name]             (derived from your directory name)
  Region:       Amsterdam, Netherlands (this is the fastest region for you)
  App Machines: shared-cpu-1x, 1GB RAM (most apps need about 1GB of RAM)
  Postgres:     <none>                 (not requested)
  Redis:        <none>                 (not requested)
  Sentry:       false                  (not requested)

  ...

  ==> Building image
  ...
  ==> Building image with Docker
  ...

  Watch your deployment at https://fly.io/apps/[app-name]/monitoring
  ...

  Visit your newly deployed app at https://[app-name].fly.dev/

  ```
</CodeGroup>

This will generate a `fly.toml` file with the configuration for your app and a Dockerfile that uses [multi-stage builds](/python/the-basics/multi-stage-builds).
Refer to the [fly.toml docs](/reference/configuration) for more configuration options.

To deploy a new version of your app, simply run `fly deploy` in the project directory.

You can check out the full (yet minimal) example in [this GitHub repository](https://github.com/fly-apps/) for a reference.