Build an API with Lambda and API Gateway

Back to AWS for Developers
Arjit Sharma
01 Min

Let’s build a simple REST API using AWS Lambda and API Gateway. This API will respond to HTTP GET requests.

Step 1: Create a Lambda Function

  • Go to the AWS Lambda Console.
  • Click Create function.
  • Choose Author from scratch.
  • Function name as HelloFunction and Runtime as Node.js
  • In the Function code section, use this basic example
exports.handler = async (event) => {
    return {
        statusCode: 200,
        body: JSON.stringify({ message: "Hello from Lambda!" }),
    };
};
  • Click Deploy to save your code.

Step 2: Add Execution Permissions

Ensure your Lambda function has permissions to be triggered by API Gateway:

  • Go to the Permissions tab of your Lambda function.
  • Under Execution role, click the role name to go to IAM.
  • Attach the AWSLambdaBasicExecutionRole if not already attached.

Step 3: Create a REST API in API Gateway

  • Go to the API Gateway Console.
  • Click Create API.
  • Choose REST API (not private).
  • Select New API and enter:
    • API name: MyAPI
    • Endpoint Type: Regional

Step 4: Create a Resource and Method

  • In your new API, under Resources, click Actions > Create Resource.
  • Enter:
    • Resource Name: hello
    • Resource Path: /hello
  • With the resource selected, click Actions > Create Method > GET.
  • Choose:
    • Integration type: Lambda Function
    • Check Use Lambda Proxy integration
    • Enter the function name: HelloFunction
  • Click Save. Confirm to give API Gateway permission to invoke Lambda.

Step 5: Deploy the API

  • Click Actions > Deploy API.
  • Choose:
    • Deployment stage: [New Stage]
    • Stage name: prod
  • Click Deploy.

You’ll receive a public Invoke URL, e.g.:

https://<api-id>.execute-api.<region>.amazonaws.com/prod/hello

Step 6: Test Your API

Use curl, Postman, or a browser:

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

Expected output:

{"message": "Hello from Lambda!"}
Next →