Creating an API Gateway with AWS SAM and Node.js

If you're building a serverless application with Lambda, chances are you need to expose your functions as APIs. That's where Amazon API Gateway comes in — and AWS SAM makes it incredibly easy to define and deploy them.

In this post, you’ll learn how to:

• Define an API Gateway in template.yml
  


• Connect it to a Lambda function


• Understand the difference between REST API and HTTP API in terms of performance and cost

🧱 Step 1: Define the Lambda Function

Here’s a simple function that responds to HTTP requests:

Resources:

  HelloWorldFunction:

    Type: AWS::Serverless::Function

    Properties:

      Handler: index.handler

      Runtime: nodejs22.x

      Events:

        HelloWorldApi:

          Type: Api

          Properties:

            Path: /hello

            Method: get

This tells SAM to automatically provision an API Gateway and connect it to your Lambda. The Path and Method define the route.

💡 Optional: Define the API Resource Explicitly

To configure advanced settings (like CORS or API type), you can explicitly define an API Gateway:

Globals:

  Api:

    Name: MyApi

    Cors:

      AllowMethods: "'GET,POST,OPTIONS'"

      AllowHeaders: "'Content-Type'"

      AllowOrigin: "'*'"

Or define the resource yourself:

Events:

  HelloWorldApi:

    Type: Api

    Properties:

      RestApiId: !Ref MyApi

      Path: /hello

      Method: get

Then connect it to your function like this:

Events:

  HelloWorldApi:

    Type: Api

    Properties:

      RestApiId: !Ref MyApi

      Path: /hello

      Method: get

🧪 Step 2: Write the Handler Code

Here’s your basic index.ts (or index.js):

export const handler = async (event) => {

  return {

    statusCode: 200,

    body: JSON.stringify({ message: "Hello from Lambda!" }),

  };

};

⚔️ REST API vs HTTP API: Which Should You Use?

AWS offers two types of API Gateway APIs:

🚀 HTTP API (Recommended for Most Use Cases)

• Faster cold starts


• Lower cost (~70% cheaper than REST API)


• Supports most common use cases (JWT auth, CORS, etc.)


• Limited advanced features (e.g., direct VPC integration)

🧱 REST API

• More mature, full feature set


• Supports API keys, usage plans, request validation


• More expensive and slightly higher latency

TL;DR:

• Use HTTP API for most web or mobile apps


• Use REST API if you need advanced API Gateway features

To switch to HTTP API in SAM:

Events:

  HelloWorldApi:

    Type: HttpApi

    Properties:

      Path: /hello

      Method: get

Conclusion

Creating APIs with AWS SAM is incredibly simple — just define an event and SAM handles the rest. Now you can:

✅ Connect Lambda to API Gateway

✅ Choose between REST or HTTP API based on needs