FastAPI¶

A simple working code to get started

from fastapi import FastAPI

app = FastAPI()


@app.get("/")
def root():
    return {"Hello": "JK"}

@app.get("/items/{item_id}")
def get_item(item_id: int, skip: int = 0, limit: int = 30):
    return {
            "item_id": item_id,
            "limit": limit,
            "skip": skip
            }

Path Parameter¶

Path parameter is provided in python f-string style.

Query Parameter¶

Query parameters are the extra parameter that are not part of the path. In a URL they are provided after a ? and separated by &

Example : http://localhost:8000/items/4?skip=0&limit=10

If a parameter is also present in the path its a path parameter. If a parameter is of singular type like int , float , str ,bool etc... then it is a query parameter. If a parameter is a Pydantic Model then its a Request Body used in post or put calls.

Important Status Codes¶

Success Codes¶

Status Code	Description
200	Request was successful and a response body is returned
204	Request was successful but the response body is empty

Client-Side Status Codes¶

Status Code	Description
400	Bad Request
401	Unauthorized
403	Forbidden. The client (browser) is not allowed to access the requested resource.
404	Page not found

Server-Side Status Codes¶

Status Code	Description
500	Internal Server Error
502	Bad Gateway
503	Service Unavailable. The server is currently unavailable or turned off.

Testing¶

Testing of APIs are done by TestClient in Fastapi.

Import TestClient
Create a TestClient by passing your FastAPI application to it.
Create functions with a name that starts with test_ (this is standard pytest conventions).

from fastapi import FastAPI
from fastapi.testclient import TestClient

app = FastAPI()


@app.get("/")
async def read_main():
    return {"msg": "Hello World"}

Keep the testing logic in other file. Ex: test_main.py

from fastapi.testclient import TestClient


client = TestClient(app)


def test_read_main():
    response = client.get("/")
    assert response.status_code == 200
    assert response.json() == {"msg": "Hello World"}

Debugging¶

You can debug your FastAPI application using the following code snippet. Run the code with the VS Code Python debugger enabled.

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)

FastAPI deployment¶

To deploy an application means to perform the necessary steps to make it available to users.

Ensure that you use the appropriate version of FastAPI that is best suited for your production application. Using a dependency management tool like uv will handle this automatically.

fastapi[standard]>=0.112.0,<0.113.0

WARNING: Do not specify a version for the starlette library.

IMPORTANT : It is a common practice to have one program/HTTP server (TLS Termination Proxy) running on the server (the machine, host, etc.) and managing all the HTTPS parts like receiving the encrypted HTTPS requests, sending the decrypted HTTP requests to the actual HTTP application running in the same server (the FastAPI application, in this case), take the HTTP response from the application, encrypt it using the appropriate HTTPS certificate and sending it back to the client using HTTPS.

TLS Termination Proxy¶

Traefik (has certificate renewal feature)
Caddy (has certificate renewal feature)
Nginx (certbot can be used for cert renewal)
Kubernetes with an Ingress Controller like Nginx ✅