Rate limiting in FastAPI - Mini Project: Build & Apply

Rate Limiting with FastAPI

📖 Scenario: You are building a simple API with FastAPI that serves user data. To protect your API from too many requests, you want to add rate limiting.

🎯 Goal: Create a FastAPI app that limits the number of requests a client can make within a time window.

📋 What You'll Learn

Create a FastAPI app instance named app

Define a dictionary called request_counts to track requests per client IP

Set a limit variable called MAX_REQUESTS to 5

Implement a dependency function rate_limiter that checks and updates request counts

Apply the rate_limiter dependency to a GET endpoint /data

Return a JSON response with {'message': 'Here is your data'} if under limit

Return a 429 HTTP error if the client exceeds the limit

💡 Why This Matters

🌍 Real World

APIs often need to protect themselves from too many requests that can overload servers or cause abuse. Rate limiting helps keep services stable and fair.

💼 Career

Backend developers frequently implement rate limiting to ensure APIs are reliable and secure under heavy traffic.

1

Create the FastAPI app and request tracking dictionary

Create a FastAPI app instance called app and a dictionary called request_counts to store the number of requests per client IP.

FastAPI

from fastapi import FastAPI

# Your code here

Need a hint?

Use app = FastAPI() to create the app and request_counts = {} for the dictionary.

2

Set the maximum requests limit

Add a variable called MAX_REQUESTS and set it to 5 to limit the number of requests per client.

FastAPI

from fastapi import FastAPI

app = FastAPI()
request_counts = {}

# Your code here

Need a hint?

Just create a variable MAX_REQUESTS and assign it the value 5.

3

Create the rate limiting dependency function

Write a function called rate_limiter that takes request from fastapi.Request. Inside, get the client IP from request.client.host. Increase the count in request_counts for that IP. If the count is greater than MAX_REQUESTS, raise fastapi.HTTPException with status code 429 and detail 'Too many requests'.

FastAPI

from fastapi import FastAPI

app = FastAPI()
request_counts = {}

MAX_REQUESTS = 5

# Your code here

Need a hint?

Use request.client.host to get the IP and update request_counts. Raise HTTPException if over limit.

4

Add the GET endpoint with rate limiting

Create a GET endpoint /data using @app.get('/data'). Add the rate_limiter function as a dependency using Depends. The endpoint should return a dictionary {'message': 'Here is your data'}.

FastAPI

from fastapi import FastAPI, Request, HTTPException, Depends

app = FastAPI()
request_counts = {}

MAX_REQUESTS = 5

def rate_limiter(request: Request):
    client_ip = request.client.host
    count = request_counts.get(client_ip, 0) + 1
    request_counts[client_ip] = count
    if count > MAX_REQUESTS:
        raise HTTPException(status_code=429, detail='Too many requests')

# Your code here

Need a hint?

Use @app.get('/data') and add Depends(rate_limiter) as a parameter to the endpoint function.