Serverless AWS Lambda Development · Lesson

Invoking Lambda with API Gateway

Configure API Gateway to act as an HTTP endpoint for your Lambda functions, enabling them to serve web requests and build RESTful APIs.

Invoking Lambda with API Gateway is a free Serverless AWS Lambda Development lesson on CoddyKit — lesson 2 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Serverless AWS Lambda Development learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Your Lambda's Front Door

Imagine you have a fantastic serverless function, but how do people access it from a web browser or another application? That's where Amazon API Gateway comes in!

API Gateway acts as the "front door" for your applications. It's a fully managed service that helps developers create, publish, maintain, monitor, and secure APIs at any scale.

Why Pair API Gateway with Lambda?

Lambda functions are great for running code without managing servers. But by themselves, they don't have public HTTP endpoints accessible over the internet.

API Gateway provides these endpoints, transforming simple Lambda functions into powerful, accessible web services. This combination is a core pattern for building serverless RESTful APIs.

Turning Lambda into an HTTP Endpoint

When you integrate Lambda with API Gateway, API Gateway handles the incoming HTTP request and routes it to your Lambda function. After your Lambda processes the request and returns a response, API Gateway takes that response and sends it back to the client.

Client Request: Browser or app sends HTTP request.
API Gateway: Receives, authenticates, and routes request.
Lambda Invocation: API Gateway triggers your Lambda.
Lambda Response: Lambda processes and returns data.
Client Response: API Gateway formats and sends response back.

Simplified Lambda Proxy Integration

One of the most common ways to integrate Lambda with API Gateway is using Lambda Proxy Integration.

With proxy integration, API Gateway passes the raw HTTP request data (like headers, body, query parameters) directly to your Lambda function. Your Lambda then returns a response in a specific format that API Gateway understands, which it then uses to create the HTTP response for the client.

Building an API-Ready Lambda

For API Gateway's proxy integration, your Lambda function needs to expect an event object containing HTTP request details and return an object with statusCode, headers, and body.

Let's look at a simple Python example:

import json

def lambda_handler(event, context):
    # Log the incoming event for debugging
    print(f"Received event: {event}")

    # Extract path parameter if available
    name = "World"
    if event.get('pathParameters') and 'name' in event['pathParameters']:
        name = event['pathParameters']['name']

    # Construct the response body
    response_message = f"Hello, {name} from CoddyKit Lambda!"

    # API Gateway expects a specific response format
    return {
        'statusCode': 200,
        'headers': {
            'Content-Type': 'application/json'
        },
        'body': json.dumps(response_message)
    }

Lambda Response Format

The Python Lambda function we saw returns a dictionary. API Gateway uses this dictionary to construct the HTTP response sent back to the client.

statusCode: The HTTP status code (e.g., 200 for success).
headers: A dictionary of HTTP response headers.
body: The actual response content, which must be a string (often JSON stringified).

This strict format ensures API Gateway can correctly translate your Lambda's output into a standard HTTP response.

Setting Up the API Endpoint

To connect your Lambda function, you'd typically:

Create a new REST API in API Gateway.
Define a Resource (e.g., /hello or /hello/{name} for path parameters).
Add a Method (e.g., GET) to your resource.
Configure the method to use Lambda Proxy Integration, pointing to your Lambda function.
Grant API Gateway permission to invoke your Lambda.

These steps create the bridge between your HTTP request and your serverless function.

Deploying Your API

After configuring your API Gateway resources and methods, you need to deploy the API to a stage.

A stage is a logical reference to a lifecycle state of your API (e.g., dev, test, prod). Deploying creates a publicly accessible URL for your API, like https://abcdefg.execute-api.us-east-1.amazonaws.com/dev/hello.

You can then use this URL to send HTTP requests to your Lambda function.

Invoking Your New API

Once deployed, you can test your API endpoint using tools like a web browser, curl, or Postman.

For example, if your API is deployed to /dev/hello/{name}, you could visit:

https://your-api-id.execute-api.region.amazonaws.com/dev/hello/Coddy

This would invoke your Lambda, which would then return a "Hello, Coddy from CoddyKit Lambda!" message.

API Gateway Integration Check

You've learned how API Gateway acts as a front door for Lambda. Let's test your understanding of how these services work together.

Recap: API Gateway & Lambda

In this lesson, we discovered how Amazon API Gateway transforms your Lambda functions into accessible HTTP endpoints. You learned:

API Gateway acts as the "front door" for serverless applications.
Lambda Proxy Integration simplifies passing requests and responses.
The specific response format your Lambda needs to return.
The conceptual steps to define, deploy, and test your API.

This powerful combination is fundamental for building serverless web APIs!

Frequently asked questions

Is the “Invoking Lambda with API Gateway” lesson free?

Yes — the full text of “Invoking Lambda with API Gateway” is free to read here on the web, and the Serverless AWS Lambda Development course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Serverless AWS Lambda Development course, upgrade to CoddyKit PRO.

What will I learn in “Invoking Lambda with API Gateway”?

Configure API Gateway to act as an HTTP endpoint for your Lambda functions, enabling them to serve web requests and build RESTful APIs. You practise Serverless AWS Lambda Development with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Serverless AWS Lambda Development?

No prior experience is required. Serverless AWS Lambda Development on CoddyKit is structured for beginners through advanced learners; this is — lesson 2 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Invoking Lambda with API Gateway” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Serverless AWS Lambda Development lesson?

Yes. Every Serverless AWS Lambda Development lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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