How to Deploy a FastAPI Application on AWS Lambda with Serverless Framework

In today's fast-paced digital landscape, deploying applications efficiently is crucial for developers and businesses alike. FastAPI, a modern web framework for building APIs with Python, combined with AWS Lambda, a serverless compute service, offers an excellent solution for scalable and cost-effective application deployment. In this guide, we’ll walk through the steps to deploy a FastAPI application on AWS Lambda using the Serverless Framework, providing practical insights, code examples, and troubleshooting tips along the way.

What is FastAPI?

FastAPI is a high-performance web framework specifically designed for building APIs quickly and efficiently. Leveraging Python type hints, it provides automatic interactive API documentation through Swagger UI and ReDoc. FastAPI is ideal for applications requiring speed and performance, making it a popular choice among developers.

Use Cases for FastAPI

• Microservices: FastAPI is lightweight and efficient, making it suitable for microservices architecture.
• Data Science Applications: Its ability to handle asynchronous requests is beneficial for machine learning and data processing workloads.
• IoT Applications: FastAPI can efficiently manage numerous simultaneous connections, making it a good fit for IoT.

What is AWS Lambda?

AWS Lambda is a serverless computing service that lets you run code without provisioning or managing servers. You only pay for the compute time you consume, making it a cost-effective solution for running applications. Lambda automatically scales your application by running code in response to events such as HTTP requests via API Gateway.

Benefits of Using AWS Lambda

• Cost Efficiency: Pay only for what you use.
• Automatic Scaling: Handles varying loads seamlessly.
• Integration with AWS Services: Easily connects with other AWS services.

Setting Up Your Environment

Before we dive into the code, ensure you have the following prerequisites:

1. AWS Account: Sign up if you don’t have one.
2. Node.js and NPM: Install Node.js which comes with NPM.
3. Python 3.6+: Make sure you have Python installed.
4. Serverless Framework: Install globally using NPM:

bash npm install -g serverless

1. AWS CLI: Install the AWS Command Line Interface and configure it with your credentials:

bash aws configure

Step 1: Create a FastAPI Application

Let’s begin by creating a simple FastAPI application. Create a new directory for your project:

mkdir fastapi-lambda && cd fastapi-lambda

Then, create a virtual environment and install FastAPI and Uvicorn:

python -m venv venv
source venv/bin/activate  # On Windows use `venv\Scripts\activate`
pip install fastapi uvicorn

Now, create a main.py file and add the following code:

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"Hello": "World"}

@app.get("/items/{item_id}")
def read_item(item_id: int):
    return {"item_id": item_id}

Step 2: Initialize the Serverless Framework

Next, initialize a new Serverless service in your project directory:

serverless create --template aws-python3 --path fastapi-service
cd fastapi-service

This command will create a basic Serverless service structure.

Step 3: Configure the Serverless Framework

Edit the serverless.yml file to configure the service. Here’s a basic example:

service: fastapi-service

provider:
  name: aws
  runtime: python3.8
  region: us-east-1

functions:
  app:
    handler: main.app
    events:
      - http:
          path: /
          method: get
      - http:
          path: items/{item_id}
          method: get

Note on Handler Configuration

In the serverless.yml, the handler points to the FastAPI app. The Serverless Framework will use this to connect incoming requests to your FastAPI application.

Step 4: Deploying to AWS Lambda

Now that everything is set up, deploy your FastAPI application to AWS Lambda:

serverless deploy

After a successful deployment, you’ll see an output with the endpoints for your API.

Step 5: Testing Your API

You can test your FastAPI endpoints using tools like Postman or curl. For example, to test the root endpoint, use:

curl https://your-api-id.execute-api.us-east-1.amazonaws.com/dev/

You should receive a JSON response:

{"Hello": "World"}

Troubleshooting Common Issues

1. Cold Start: AWS Lambda functions may experience latency on the first request. Optimize function performance by keeping dependencies lightweight or using provisioned concurrency.

2. Timeouts: Ensure your function has sufficient timeout settings in the serverless.yml. The default timeout is 6 seconds; you can extend it as needed.

yaml provider: timeout: 30 # Increase timeout to 30 seconds

1. CORS Issues: If you encounter CORS errors, configure CORS settings in your serverless.yml under the http event:

yaml events: - http: path: / method: get cors: true

Conclusion

Deploying a FastAPI application on AWS Lambda using the Serverless Framework is a straightforward process that offers numerous benefits, including scalability and cost-efficiency. With this guide, you should have a solid foundation to create and deploy your FastAPI applications in a serverless environment. Experiment with more complex features like database integration or asynchronous processing to fully harness the power of FastAPI and AWS Lambda. Happy coding!