FastAPI CLI¶
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FastAPI CLI is a command line program that you can use to serve your FastAPI app, manage your FastAPI project, and more.
When you install FastAPI (e.g. with pip install "fastapi[standard]"), it includes a package called fastapi-cli, this package provides the fastapi command in the terminal.
To run your FastAPI app for development, you can use the fastapi dev command:
$ <font color="#4E9A06">fastapi</font> dev <u style="text-decoration-style:single">main.py</u>
<font color="#3465A4">INFO </font> Using path <font color="#3465A4">main.py</font>
<font color="#3465A4">INFO </font> Resolved absolute path <font color="#75507B">/home/user/code/awesomeapp/</font><font color="#AD7FA8">main.py</font>
<font color="#3465A4">INFO </font> Searching for package file structure from directories with <font color="#3465A4">__init__.py</font> files
<font color="#3465A4">INFO </font> Importing from <font color="#75507B">/home/user/code/</font><font color="#AD7FA8">awesomeapp</font>
╭─ <font color="#8AE234"><b>Python module file</b></font> ─╮
│ │
│ 🐍 main.py │
│ │
╰──────────────────────╯
<font color="#3465A4">INFO </font> Importing module <font color="#4E9A06">main</font>
<font color="#3465A4">INFO </font> Found importable FastAPI app
╭─ <font color="#8AE234"><b>Importable FastAPI app</b></font> ─╮
│ │
│ <span style="background-color:#272822"><font color="#FF4689">from</font></span><span style="background-color:#272822"><font color="#F8F8F2"> main </font></span><span style="background-color:#272822"><font color="#FF4689">import</font></span><span style="background-color:#272822"><font color="#F8F8F2"> app</font></span><span style="background-color:#272822"> </span> │
│ │
╰──────────────────────────╯
<font color="#3465A4">INFO </font> Using import string <font color="#8AE234"><b>main:app</b></font>
<span style="background-color:#C4A000"><font color="#2E3436">╭────────── FastAPI CLI - Development mode ───────────╮</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ Serving at: http://127.0.0.1:8000 │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ API docs: http://127.0.0.1:8000/docs │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ Running in development mode, for production use: │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ </font></span><span style="background-color:#C4A000"><font color="#555753"><b>fastapi run</b></font></span><span style="background-color:#C4A000"><font color="#2E3436"> │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">│ │</font></span>
<span style="background-color:#C4A000"><font color="#2E3436">╰─────────────────────────────────────────────────────╯</font></span>
<font color="#4E9A06">INFO</font>: Will watch for changes in these directories: ['/home/user/code/awesomeapp']
<font color="#4E9A06">INFO</font>: Uvicorn running on <b>http://127.0.0.1:8000</b> (Press CTRL+C to quit)
<font color="#4E9A06">INFO</font>: Started reloader process [<font color="#34E2E2"><b>2265862</b></font>] using <font color="#34E2E2"><b>WatchFiles</b></font>
<font color="#4E9A06">INFO</font>: Started server process [<font color="#06989A">2265873</font>]
<font color="#4E9A06">INFO</font>: Waiting for application startup.
<font color="#4E9A06">INFO</font>: Application startup complete.
The command line program called fastapi is FastAPI CLI.
FastAPI CLI takes the path to your Python program (e.g. main.py) and automatically detects the FastAPI instance (commonly named app), determines the correct import process, and then serves it.
For production you would use fastapi run instead. 🚀
Internally, FastAPI CLI uses Uvicorn, a high-performance, production-ready, ASGI server. 😎
fastapi dev¶
Running fastapi dev initiates development mode.
By default, auto-reload is enabled, automatically reloading the server when you make changes to your code. This is resource-intensive and could be less stable than when it's disabled. You should only use it for development. It also listens on the IP address 127.0.0.1, which is the IP for your machine to communicate with itself alone (localhost).
fastapi run¶
Executing fastapi run starts FastAPI in production mode by default.
By default, auto-reload is disabled. It also listens on the IP address 0.0.0.0, which means all the available IP addresses, this way it will be publicly accessible to anyone that can communicate with the machine. This is how you would normally run it in production, for example, in a container.
In most cases you would (and should) have a "termination proxy" handling HTTPS for you on top, this will depend on how you deploy your application, your provider might do this for you, or you might need to set it up yourself.
Tip
You can learn more about it in the deployment documentation.