aws-serverless

# AWS Serverless ## Patterns ### Lambda Handler Pattern Proper Lambda function structure with error handling **When to use**: ['Any Lambda function implementation', 'API handlers, event processors, scheduled tasks'] ```python ```javascript // 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 # 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 i ``` ### 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'] ```javascript ```yaml # 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: Type: AWS::Serverless::Function Properties: Handler: src/handlers/get.handler Events: GetItem: Type: HttpApi Properties: ApiId: !Ref HttpApi Path: /items/{id} Method: GET Policies: - DynamoDBReadPolicy: TableName: !Ref ItemsTable CreateItemFunction: Type: AWS::Serverless::Function Properties: Handler: src/handlers/create.handler Events: CreateItem: Type: HttpApi Properties: ApiId: !Ref HttpApi Path: /items Method: POST Policies: - DynamoDBCrudPolicy: TableName: !Ref ItemsTable # DynamoDB Table ItemsTable: Type: AWS::DynamoDB::Table Properties: AttributeDefinitions: - AttributeName: id AttributeType: S KeySchema: - AttributeName: id KeyType: HASH BillingMode: PAY_PER_REQUEST Outputs: ApiUrl: Value: !Sub "https://${HttpApi}.execute-api.${AWS::Region}.amazonaws.com/prod" ``` ```javascript // src/handlers/get.js const { getItem } = require('../lib/dynamodb'); exports.handler = async (event) => { const id = event.pathParameters?.id; if (!id) { return { statusCode: 400, body: JSON.stringify({ error: 'Missing id parameter' }) }; } const item = ``` ### Event-Driven SQS Pattern Lambda triggered by SQS for reliable async processing **When to use**: ['Decoupled, asynchronous processing', 'Need retry logic and DLQ', 'Processing messages in batches'] ```python ```yaml # template.yaml Resources: ProcessorFunction: Type: AWS::Serverless::Function Properties: Handler: src/handlers/processor.handler Events: SQSEvent: Type: SQS Properties: Queue: !GetAtt ProcessingQueue.Arn BatchSize: 10 FunctionResponseTypes: - ReportBatchItemFailures # Partial batch failure handling ProcessingQueue: Type: AWS::SQS::Queue Properties: VisibilityTimeout: 180 # 6x Lambda timeout RedrivePolicy: deadLetterTargetArn: !GetAtt DeadLetterQueue.Arn maxReceiveCount: 3 DeadLetterQueue: Type: AWS::SQS::Queue Properties: MessageRetentionPeriod: 1209600 # 14 days ``` ```javascript // src/handlers/processor.js exports.handler = async (event) => { const batchItemFailures = []; for (const record of event.Records) { try { const body = JSON.parse(record.body); await processMessage(body); } catch (error) { console.error(`Failed to process message ${record.messageId}:`, error); // Report this item as failed (will be retried) batchItemFailures.push({ itemIdentifier: record.messageId }); } } // Return failed items for retry return { batchItemFailures }; }; async function processMessage(message) { // Your processing logic console.log('Processing:', message); // Simulate work await saveToDatabase(message); } ``` ```python # Python version import json import logging logger = logging.getLogger() def handler(event, context): batch_item_failures = [] for record in event['Records']: try: body = json.loads(record['body']) process_message(body) except Exception as e: logger.error(f"Failed to process {record['messageId']}: {e}") batch_item_failures.append({ 'itemIdentifier': record['messageId'] }) return {'batchItemFailures': batch_ite ``` ## Anti-Patterns ### ❌ Monolithic Lambda **Why bad**: Large deployment packages cause slow cold starts. Hard to scale individual operations. Updates affect entire system. ### ❌ Large Dependencies **Why bad**: Increases deployment package size. Slows down cold starts significantly. Most of SDK/library may be unused. ### ❌ Synchronous Calls in VPC **Why bad**: VPC-attached Lambdas have ENI setup overhead. Blocking DNS lookups or connections worsen cold starts. ## ⚠️ Sharp Edges | Issue | Severity | Solution | |-------|----------|----------| | Issue | high | ## Measure your INIT phase | | Issue | high | ## Set appropriate timeout | | Issue | high | ## Increase memory allocation | | Issue | medium | ## Verify VPC configuration | | Issue | medium | ## Tell Lambda not to wait for event loop | | Issue | medium | ## For large file uploads | | Issue | high | ## Use different buckets/prefixes | --- > Converted and distributed by [TomeVault](https://tomevault.io) | [Claim this content](https://tomevault.io/claim/davila7/claude-code-templates) <!-- tomevault:2.0:skill_md:2026-04-05 -->