AWS Lambda & API Gateway

AWS Lambda is a serverless compute service that lets you run code without provisioning or managing servers. Amazon API Gateway is a fully managed service that enables developers to create, publish, maintain, and secure APIs at scale. Together, they allow you to build scalable serverless applications with minimal infrastructure management.

This guide provides an overview of AWS Lambda and API Gateway, including how to set them up using the AWS Console (UI) and how to use them programmatically with the AWS CLI and SDKs. It also includes an example of invoking Lambda from API Gateway.

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AWS Lambda Overview

• Event-driven compute service that executes code in response to events.
• Supports multiple runtimes (Python, Node.js, Java, Go, .NET, Ruby).
• Automatically scales with demand.
• Billed per request and execution duration.

Key Components

• Function: The unit of deployment (your code).
• Trigger: Event source that invokes the Lambda (e.g., API Gateway, S3, DynamoDB, CloudWatch).
• Execution Role: IAM role Lambda uses to access other AWS services.

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API Gateway Overview

• Fully managed service for creating and deploying REST, HTTP, and WebSocket APIs.
• Provides authentication, authorization, rate limiting, caching, monitoring, and logging.
• Can trigger AWS Lambda functions directly as backends.

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Using AWS Console (UI)

Create a Lambda Function

1. Open the AWS Management Console.
2. Navigate to Lambda → Functions → Create function.
3. Choose Author from scratch.
4. Enter function name (e.g., HelloWorldLambda).
5. Choose runtime (e.g., Python 3.10).
6. Choose or create an execution role.
7. Click Create function.

8. Add handler code (example Python):

   def lambda_handler(event, context):
       return {
           'statusCode': 200,
           'body': 'Hello from Lambda!'
       }
   

9. Click Deploy.

Create an API Gateway to Trigger Lambda

1. In the AWS Console, navigate to API Gateway.
2. Click Create API → choose HTTP API.
3. Provide an API name (e.g., HelloWorldAPI).
4. Under Integrations, choose Lambda and select your function.
5. Configure routes (e.g., GET /hello).
6. Deploy the API.
7. Copy the endpoint URL and test with a browser or curl.

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Developer (SDK/CLI) Usage

Invoke Lambda with AWS CLI

aws lambda invoke \
  --function-name HelloWorldLambda \
  --payload '{"key":"value"}' \
  response.json

Deploy API Gateway with AWS CLI

aws apigatewayv2 create-api \
  --name "HelloWorldAPI" \
  --protocol-type HTTP \
  --target arn:aws:lambda:us-east-1:123456789012:function:HelloWorldLambda

Python (boto3) Example: Invoke Lambda

import boto3
import json

client = boto3.client('lambda')

response = client.invoke(
    FunctionName='HelloWorldLambda',
    Payload=json.dumps({"message": "Hello"})
)

print(response['Payload'].read().decode())

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Example: API Gateway Triggering Lambda

Step 1: Lambda Function (Python)

def lambda_handler(event, context):
    name = event.get("queryStringParameters", {}).get("name", "World")
    return {
        'statusCode': 200,
        'body': f"Hello, {name}!"
    }

Step 2: API Gateway Route

• Create route: GET /greet
• Integration: Link to the Lambda function.

Step 3: Test the Endpoint

curl "https://<api-id>.execute-api.us-east-1.amazonaws.com/greet?name=John"

Response:

{
  "statusCode": 200,
  "body": "Hello, John!"
}

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Best Practices

• IAM Roles: Use least-privilege IAM roles for Lambda and API Gateway execution.
• Error Handling: Implement structured error responses for Lambda functions.
• Logging: Use CloudWatch Logs for monitoring and debugging.
• Security: Protect APIs with IAM auth, Cognito, or Lambda authorizers.
• Performance: Keep functions lightweight and use environment variables for configuration.

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Common Use Cases

• Serverless REST APIs with Lambda backends.
• Webhook processing (e.g., from third-party services).
• IoT data ingestion via HTTP endpoints.
• Microservices architecture using multiple Lambda functions behind API Gateway.

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Summary

AWS Lambda and API Gateway form the backbone of serverless applications. Developers can use:

• AWS Console (UI) for quick setup and testing.
• AWS CLI and SDKs for automation and integration.

With API Gateway invoking Lambda functions, you can build scalable, secure, and cost-effective serverless APIs with minimal operational overhead.