How to Deploy a Flask REST API on AWS Lambda

In today's fast-paced development environment, deploying applications in a serverless architecture has become increasingly popular. AWS Lambda allows developers to run code without provisioning or managing servers, making it ideal for deploying a Flask REST API. In this article, we'll walk through the process of deploying a Flask REST API on AWS Lambda, covering everything from setup to code snippets, and troubleshooting tips.

What is Flask?

Flask is a lightweight WSGI web application framework in Python. It’s designed to make web development easy and straightforward. Flask is often used for building REST APIs due to its flexibility and simplicity. It allows developers to easily create routes, handle HTTP requests, and integrate with databases.

Why Use AWS Lambda?

AWS Lambda provides a serverless computing environment where you can run your code in response to events without the need to manage servers. Some advantages of using AWS Lambda include:

• Cost Efficiency: You pay only for the compute time you consume.
• Scalability: Automatically scales your application in response to incoming requests.
• Maintenance-Free: No need to manage servers, allowing you to focus on developing your application.

Prerequisites

Before we begin, ensure you have the following:

• An AWS account
• Python installed on your machine (preferably version 3.6 or higher)
• Basic knowledge of Flask
• AWS CLI installed and configured

Step-by-Step Guide to Deploy a Flask REST API on AWS Lambda

Step 1: Set Up Your Flask Application

First, let's create a simple Flask application. Create a new directory for your project and navigate into it.

mkdir flask_lambda
cd flask_lambda

Next, create a file named app.py and add the following code:

from flask import Flask, jsonify, request

app = Flask(__name__)

@app.route('/api/hello', methods=['GET'])
def hello():
    return jsonify({'message': 'Hello, World!'})

if __name__ == '__main__':
    app.run(debug=True)

Step 2: Install Dependencies

You will need to use the Flask library and gunicorn for running your application. Install them using pip:

pip install flask gunicorn

Step 3: Create a Lambda Function

1. Zip Your Application: AWS Lambda requires your application to be in a ZIP format. To prepare your application, run:

   bash zip -r flask_lambda.zip app.py

2. Create a Lambda Function: Log into your AWS Management Console, navigate to the Lambda service, and click "Create function."

3. Configure the Function:

4. Choose "Author from scratch."
5. Provide a name for your function (e.g., FlaskLambdaFunction).
6. Set the runtime to Python 3.x.
7. Choose or create an IAM role with permissions to run Lambda functions.

Step 4: Add AWS API Gateway

AWS API Gateway acts as the interface for your Flask app. Follow these steps:

1. Create a New API: In the AWS API Gateway console, click on "Create API."

2. Select REST API: Choose the REST API option and click "Build."

3. Configure Your API:

4. Enter a name for your API.

5. Set up resource paths, e.g., /api/hello.

6. Create a Method:

7. Select the resource you created.
8. Click "Actions" and then choose "Create Method."
9. Select "GET" and integrate it with your Lambda function.

Step 5: Deploy Your API

1. Create a Deployment Stage: In the API Gateway console, click "Actions" and select "Deploy API."

2. Set Up the Stage: Create a new stage (e.g., prod) and deploy your API.

3. Invoke Your API: After deployment, you’ll receive an endpoint URL. You can test your API using curl or Postman:

curl https://your-api-id.execute-api.region.amazonaws.com/prod/api/hello

Step 6: Testing and Troubleshooting

• Testing: Make sure your API is returning the expected response.
• CloudWatch Logs: If you run into issues, check AWS CloudWatch for logs related to your Lambda function.
• Timeouts: Adjust the timeout settings if your function takes longer to execute than expected.

Best Practices for Flask on Lambda

• Keep Functions Lightweight: Avoid long-running processes and limit the size of your deployment package.
• Use Environment Variables: Securely manage configuration settings and secrets.
• Implement CORS: If you're planning to access your API from a web application, configure CORS in API Gateway.

Conclusion

Deploying a Flask REST API on AWS Lambda is a straightforward process that allows you to leverage serverless architecture effectively. By following these steps, you can set up, deploy, and manage your API without worrying about server maintenance. With the scalability and cost-efficiency of AWS Lambda, your Flask application can handle varying loads while allowing you to focus on building great features. Happy coding!