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How to Connect API Gateway and Lambda In 2 Easy Steps

Jainish Patel
API Gateway and Lambda Feature Image

Welcome, tech enthusiasts and professionals! 🌟 Today, we’re diving into the process of integrating AWS API Gateway with a Lambda function. This guide will walk you through each step, ensuring you have a seamless experience. Let’s get started!

Meet the Characters

  • Lenny the Lambda: A versatile robot designed to handle various tasks.
  • Gwen the Gateway: A powerful API Gateway that facilitates communication.
  • Pat the Postman: A reliable tool for testing and delivering messages.

The Problem Statement

I was recently looking for a comprehensive document on how to integrate AWS API Gateway with Lambda function, but I couldn’t find a single end-to-end guide. So, I decided to create one myself! This guide will cover everything from setting up your Lambda function to testing your API Gateway endpoints with Postman, and even troubleshooting common issues.

Creating Your Lambda Function

First, let’s create our Lambda function, which we’ll call Lenny.

Step 1: Create a new Lambda function

  • Log in to your AWS Management Console and navigate to the Lambda service.
  • Click on Create function.
  • Choose Author from scratch.
  • Name your function, e.g., LennyTheLambda.
  • Select the runtime (e.g., Python, Node.js).
  • Click Create function.

Step 2: Write the function code

  • In the code editor, input the following code:
def lambda_handler(event, context):
    return {
        'statusCode': 200,
        'body': 'Once upon a time in the land of AWS, a Lambda function named Lenny said, "Hello, world! I am here to assist you with your tasks!"'
    }

Step 3: Deploy the function:

  • Click Deploy to save and deploy your function.

For more details, refer to the AWS Lambda documentation.

Setting Up API Gateway

Next, we’ll set up an API Gateway, which we’ll call Gwen, to expose our Lambda function as an HTTP endpoint.

Step 1: Create a new API:

  • Navigate to the API Gateway service.
  • Click on Create API.
  • Choose REST API > Build.
  • Name your API, e.g., GwenAPI.
  • Click on Create API.

Step 2: Integrate with Lambda:

  • Click on Create resource.
  • Name your resource, e.g., CallingLenny.
  • Click on Create resource.
  •  Click on Create method.
  • Select method type as GET.
  • Select Lambda and choose the Lambda function you created.
  • Click Create method. 

Step 3: Deploy the API:

  • Click on Deploy API.
  • Provide your stage name, e.g., Test
  • Click Deploy.
  • Note the Invoke URL provided. This is your API endpoint.

For more details, refer to the Amazon API Gateway documentation.

Testing with Postman

Let’s test our API endpoint using Postman, which we’ll call Pat.

  1. Open Postman and create a new request.
  2. Set the request type to GET.
  3. Enter the Invoke URL from API Gateway.
  4. Send the request.

You should see a response saying, 

Once upon a time in the land of AWS, a Lambda function named Lenny said, "Hello, world! I am here to assist you with your tasks!"

The Unexpected Twist

Just when everything seemed perfect, an unexpected error appeared: “Error 500: Internal Server Error.” Let’s troubleshoot this issue.

  1. Investigate the Error:
    • Check the logs in the AWS Management Console.
    • Identify the issue in the code.
  1. Fix the Bug:
    • Correct the code and redeploy the function.
  1. Test Again:
    • Use Postman to send another request.
    • Ensure the message is delivered correctly.

Common Configuration Errors and Resolutions

Here are some common issues you might encounter and how to resolve them:

  1. Permission Errors:
    • If you see a 403 Forbidden error, ensure your Lambda function has the necessary permissions.
    • Go to the Lambda function’s Permissions tab and add an API Gateway trigger.
  1. Timeout Issues:
    • If your function takes too long to respond, increase the timeout setting in the Lambda function configuration.
  1. Invalid Response Format:
    • Ensure your Lambda function returns a properly formatted response with statusCode and body fields.

Expert Tips

Here are some tips from the experts:

  • Keep it Simple: Start with basic functions and gradually add complexity.
  • Test Frequently: Use tools like Postman to test your API regularly.
  • Utilize Documentation: AWS provides extensive documentation to help you understand and troubleshoot issues.

Conclusion

Congratulations! You’ve successfully integrated API Gateway with a Lambda function and tested it using Postman. By understanding and resolving common issues, you’re well on your way to mastering AWS integrations. If you have any questions or need further assistance, feel free to leave a comment. Happy coding!

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