ranbot-ai/aws-serverless

AWS Serverless

Specialized skill for building production-ready serverless applications on AWS. Covers Lambda functions, API Gateway, DynamoDB, SQS/SNS event-driven patterns, SAM/CDK deployment, and cold start optimization.

Principles

• Right-size memory and timeout (measure before optimizing)
• Minimize cold starts for latency-sensitive workloads
• Use SnapStart for Java/.NET functions
• Prefer HTTP API over REST API for simple use cases
• Design for failure with DLQs and retries
• Keep deployment packages small
• Use environment variables for configuration
• Implement structured logging with correlation IDs

Patterns

Lambda Handler Pattern

Proper Lambda function structure with error handling

When to use: Any Lambda function implementation,API handlers, event processors, scheduled tasks

// Node.js Lambda Handler
// handler.js

// Initialize outside handler (reused across invocations)
const { DynamoDBClient } = require('@aws-sdk/client-dynamodb');
const { DynamoDBDocumentClient, GetCommand } = require('@aws-sdk/lib-dynamodb');

const client = new DynamoDBClient({});
const docClient = DynamoDBDocumentClient.from(client);

// Handler function
exports.handler = async (event, context) => {
  // Optional: Don't wait for event loop to clear (Node.js)
  context.callbackWaitsForEmptyEventLoop = false;

  try {
    // Parse input based on event source
    const body = typeof event.body === 'string'
      ? JSON.parse(event.body)
      : event.body;

    // Business logic
    const result = await processRequest(body);

    // Return API Gateway compatible response
    return {
      statusCode: 200,
      headers: {
        'Content-Type': 'application/json',
        'Access-Control-Allow-Origin': '*'
      },
      body: JSON.stringify(result)
    };
  } catch (error) {
    console.error('Error:', JSON.stringify({
      error: error.message,
      stack: error.stack,
      requestId: context.awsRequestId
    }));

    return {
      statusCode: error.statusCode || 500,
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({
        error: error.message || 'Internal server error'
      })
    };
  }
};

async function processRequest(data) {
  // Your business logic here
  const result = await docClient.send(new GetCommand({
    TableName: process.env.TABLE_NAME,
    Key: { id: data.id }
  }));
  return result.Item;
}

# Python Lambda Handler
# handler.py

import json
import os
import logging
import boto3
from botocore.exceptions import ClientError

# Initialize outside handler (reused across invocations)
logger = logging.getLogger()
logger.setLevel(logging.INFO)

dynamodb = boto3.resource('dynamodb')
table = dynamodb.Table(os.environ['TABLE_NAME'])

def handler(event, context):
    try:
        # Parse input
        body = json.loads(event.get('body', '{}')) if isinstance(event.get('body'), str) else event.get('body', {})

        # Business logic
        result = process_request(body)

        return {
            'statusCode': 200,
            'headers': {
                'Content-Type': 'application/json',
                'Access-Control-Allow-Origin': '*'
            },
            'body': json.dumps(result)
        }

    except ClientError as e:
        logger.error(f"DynamoDB error: {e.response['Error']['Message']}")
        return error_response(500, 'Database error')

    except json.JSONDecodeError:
        return error_response(400, 'Invalid JSON')

    except Exception as e:
        logger.error(f"Unexpected error: {str(e)}", exc_info=True)
        return error_response(500, 'Internal server error')

def process_request(data):
    response = table.get_item(Key={'id': data['id']})
    return response.get('Item')

def error_response(status_code, message):
    return {
        'statusCode': status_code,
        'headers': {'Content-Type': 'application/json'},
        'body': json.dumps({'error': message})
    }

Best_practices

• Initialize clients outside handler (reused across warm invocations)
• Always return proper API Gateway response format
• Log with structured JSON for CloudWatch Insights
• Include request ID in error logs for tracing

API Gateway Integration Pattern

REST API and HTTP API integration with Lambda

When to use: Building REST APIs backed by Lambda,Need HTTP endpoints for functions

# template.yaml (SAM)
AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Globals:
  Function:
    Runtime: nodejs20.x
    Timeout: 30
    MemorySize: 256
    Environment:
      Variables:
        TABLE_NAME: !Ref ItemsTable

Resources:
  # HTTP API (recommended for simple use cases)
  HttpApi:
    Type: AWS::Serverless::HttpApi
    Properties:
      StageName: prod
      CorsConfiguration:
        AllowOrigins:
          - "*"
        AllowMethods:
          - GET
          - POST
          - DELETE
        AllowHeaders:
          - "*"

  # Lambda Functions
  GetItemFunction: