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+# Serverless Architecture Patterns
+
+Comprehensive patterns for building serverless applications on AWS based on Well-Architected Framework principles.
+
+## Table of Contents
+
+- [Core Serverless Patterns](#core-serverless-patterns)
+- [API Patterns](#api-patterns)
+- [Data Processing Patterns](#data-processing-patterns)
+- [Integration Patterns](#integration-patterns)
+- [Orchestration Patterns](#orchestration-patterns)
+- [Anti-Patterns](#anti-patterns)
+
+## Core Serverless Patterns
+
+### Pattern: Serverless Microservices
+
+**Use case**: Independent, scalable services with separate databases
+
+**Architecture**:
+```
+API Gateway → Lambda Functions → DynamoDB/RDS
+              ↓ (events)
+         EventBridge → Other Services
+```
+
+**CDK Implementation**:
+```typescript
+// User Service
+const userTable = new dynamodb.Table(this, 'Users', {
+  partitionKey: { name: 'userId', type: dynamodb.AttributeType.STRING },
+  billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
+});
+
+const userFunction = new NodejsFunction(this, 'UserHandler', {
+  entry: 'src/services/users/handler.ts',
+  environment: {
+    TABLE_NAME: userTable.tableName,
+  },
+});
+
+userTable.grantReadWriteData(userFunction);
+
+// Order Service (separate database)
+const orderTable = new dynamodb.Table(this, 'Orders', {
+  partitionKey: { name: 'orderId', type: dynamodb.AttributeType.STRING },
+  billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
+});
+
+const orderFunction = new NodejsFunction(this, 'OrderHandler', {
+  entry: 'src/services/orders/handler.ts',
+  environment: {
+    TABLE_NAME: orderTable.tableName,
+    EVENT_BUS: eventBus.eventBusName,
+  },
+});
+
+orderTable.grantReadWriteData(orderFunction);
+eventBus.grantPutEventsTo(orderFunction);
+```
+
+**Benefits**:
+- Independent deployment and scaling
+- Database per service (data isolation)
+- Technology diversity
+- Fault isolation
+
+### Pattern: Serverless API Backend
+
+**Use case**: REST or GraphQL API with serverless compute
+
+**REST API with API Gateway**:
+```typescript
+const api = new apigateway.RestApi(this, 'Api', {
+  restApiName: 'serverless-api',
+  deployOptions: {
+    stageName: 'prod',
+    tracingEnabled: true,
+    loggingLevel: apigateway.MethodLoggingLevel.INFO,
+    dataTraceEnabled: true,
+    metricsEnabled: true,
+  },
+  defaultCorsPreflightOptions: {
+    allowOrigins: apigateway.Cors.ALL_ORIGINS,
+    allowMethods: apigateway.Cors.ALL_METHODS,
+  },
+});
+
+// Resource-based routing
+const items = api.root.addResource('items');
+items.addMethod('GET', new apigateway.LambdaIntegration(listFunction));
+items.addMethod('POST', new apigateway.LambdaIntegration(createFunction));
+
+const item = items.addResource('{id}');
+item.addMethod('GET', new apigateway.LambdaIntegration(getFunction));
+item.addMethod('PUT', new apigateway.LambdaIntegration(updateFunction));
+item.addMethod('DELETE', new apigateway.LambdaIntegration(deleteFunction));
+```
+
+**GraphQL API with AppSync**:
+```typescript
+const api = new appsync.GraphqlApi(this, 'Api', {
+  name: 'serverless-graphql-api',
+  schema: appsync.SchemaFile.fromAsset('schema.graphql'),
+  authorizationConfig: {
+    defaultAuthorization: {
+      authorizationType: appsync.AuthorizationType.API_KEY,
+    },
+  },
+  xrayEnabled: true,
+});
+
+// Lambda resolver
+const dataSource = api.addLambdaDataSource('lambda-ds', resolverFunction);
+
+dataSource.createResolver('QueryGetItem', {
+  typeName: 'Query',
+  fieldName: 'getItem',
+});
+```
+
+### Pattern: Serverless Data Lake
+
+**Use case**: Ingest, process, and analyze large-scale data
+
+**Architecture**:
+```
+S3 (raw data) → Lambda (transform) → S3 (processed)
+                  ↓ (catalog)
+               AWS Glue → Athena (query)
+```
+
+**Implementation**:
+```typescript
+const rawBucket = new s3.Bucket(this, 'RawData');
+const processedBucket = new s3.Bucket(this, 'ProcessedData');
+
+// Trigger Lambda on file upload
+rawBucket.addEventNotification(
+  s3.EventType.OBJECT_CREATED,
+  new s3n.LambdaDestination(transformFunction),
+  { prefix: 'incoming/' }
+);
+
+// Transform function
+export const transform = async (event: S3Event) => {
+  for (const record of event.Records) {
+    const key = record.s3.object.key;
+
+    // Get raw data
+    const raw = await s3.getObject({
+      Bucket: record.s3.bucket.name,
+      Key: key,
+    });
+
+    // Transform data
+    const transformed = await transformData(raw.Body);
+
+    // Write to processed bucket
+    await s3.putObject({
+      Bucket: process.env.PROCESSED_BUCKET,
+      Key: `processed/${key}`,
+      Body: JSON.stringify(transformed),
+    });
+  }
+};
+```
+
+## API Patterns
+
+### Pattern: Authorizer Pattern
+
+**Use case**: Custom authentication and authorization
+
+```typescript
+// Lambda authorizer
+const authorizer = new apigateway.TokenAuthorizer(this, 'Authorizer', {
+  handler: authorizerFunction,
+  identitySource: 'method.request.header.Authorization',
+  resultsCacheTtl: Duration.minutes(5),
+});
+
+// Apply to API methods
+const resource = api.root.addResource('protected');
+resource.addMethod('GET', new apigateway.LambdaIntegration(protectedFunction), {
+  authorizer,
+});
+```
+
+### Pattern: Request Validation
+
+**Use case**: Validate requests before Lambda invocation
+
+```typescript
+const requestModel = api.addModel('RequestModel', {
+  contentType: 'application/json',
+  schema: {
+    type: apigateway.JsonSchemaType.OBJECT,
+    required: ['name', 'email'],
+    properties: {
+      name: { type: apigateway.JsonSchemaType.STRING, minLength: 1 },
+      email: { type: apigateway.JsonSchemaType.STRING, format: 'email' },
+    },
+  },
+});
+
+resource.addMethod('POST', integration, {
+  requestValidator: new apigateway.RequestValidator(this, 'Validator', {
+    api,
+    validateRequestBody: true,
+    validateRequestParameters: true,
+  }),
+  requestModels: {
+    'application/json': requestModel,
+  },
+});
+```
+
+### Pattern: Response Caching
+
+**Use case**: Reduce backend load and improve latency
+
+```typescript
+const api = new apigateway.RestApi(this, 'Api', {
+  deployOptions: {
+    cachingEnabled: true,
+    cacheTtl: Duration.minutes(5),
+    cacheClusterEnabled: true,
+    cacheClusterSize: '0.5', // GB
+  },
+});
+
+// Enable caching per method
+resource.addMethod('GET', integration, {
+  methodResponses: [{
+    statusCode: '200',
+    responseParameters: {
+      'method.response.header.Cache-Control': true,
+    },
+  }],
+});
+```
+
+## Data Processing Patterns
+
+### Pattern: S3 Event Processing
+
+**Use case**: Process files uploaded to S3
+
+```typescript
+const bucket = new s3.Bucket(this, 'DataBucket');
+
+// Process images
+bucket.addEventNotification(
+  s3.EventType.OBJECT_CREATED,
+  new s3n.LambdaDestination(imageProcessingFunction),
+  { suffix: '.jpg' }
+);
+
+// Process CSV files
+bucket.addEventNotification(
+  s3.EventType.OBJECT_CREATED,
+  new s3n.LambdaDestination(csvProcessingFunction),
+  { suffix: '.csv' }
+);
+
+// Large file processing with Step Functions
+bucket.addEventNotification(
+  s3.EventType.OBJECT_CREATED,
+  new s3n.SfnDestination(processingStateMachine),
+  { prefix: 'large-files/' }
+);
+```
+
+### Pattern: DynamoDB Streams Processing
+
+**Use case**: React to database changes
+
+```typescript
+const table = new dynamodb.Table(this, 'Table', {
+  partitionKey: { name: 'id', type: dynamodb.AttributeType.STRING },
+  stream: dynamodb.StreamViewType.NEW_AND_OLD_IMAGES,
+});
+
+// Process stream changes
+new lambda.EventSourceMapping(this, 'StreamConsumer', {
+  target: streamProcessorFunction,
+  eventSourceArn: table.tableStreamArn,
+  startingPosition: lambda.StartingPosition.LATEST,
+  batchSize: 100,
+  maxBatchingWindow: Duration.seconds(5),
+  bisectBatchOnError: true,
+  retryAttempts: 3,
+});
+
+// Example: Sync to search index
+export const processStream = async (event: DynamoDBStreamEvent) => {
+  for (const record of event.Records) {
+    if (record.eventName === 'INSERT' || record.eventName === 'MODIFY') {
+      const newImage = record.dynamodb?.NewImage;
+      await elasticSearch.index({
+        index: 'items',
+        id: newImage?.id.S,
+        body: unmarshall(newImage),
+      });
+    } else if (record.eventName === 'REMOVE') {
+      await elasticSearch.delete({
+        index: 'items',
+        id: record.dynamodb?.Keys?.id.S,
+      });
+    }
+  }
+};
+```
+
+### Pattern: Kinesis Stream Processing
+
+**Use case**: Real-time data streaming and analytics
+
+```typescript
+const stream = new kinesis.Stream(this, 'EventStream', {
+  shardCount: 2,
+  streamMode: kinesis.StreamMode.PROVISIONED,
+});
+
+// Fan-out with multiple consumers
+const consumer1 = new lambda.EventSourceMapping(this, 'Analytics', {
+  target: analyticsFunction,
+  eventSourceArn: stream.streamArn,
+  startingPosition: lambda.StartingPosition.LATEST,
+  batchSize: 100,
+  parallelizationFactor: 10, // Process 10 batches per shard in parallel
+});
+
+const consumer2 = new lambda.EventSourceMapping(this, 'Alerting', {
+  target: alertingFunction,
+  eventSourceArn: stream.streamArn,
+  startingPosition: lambda.StartingPosition.LATEST,
+  filters: [
+    lambda.FilterCriteria.filter({
+      eventName: lambda.FilterRule.isEqual('CRITICAL_EVENT'),
+    }),
+  ],
+});
+```
+
+## Integration Patterns
+
+### Pattern: Service Integration with EventBridge
+
+**Use case**: Decouple services with events
+
+```typescript
+const eventBus = new events.EventBus(this, 'AppBus');
+
+// Service A publishes events
+const serviceA = new NodejsFunction(this, 'ServiceA', {
+  entry: 'src/services/a/handler.ts',
+  environment: {
+    EVENT_BUS: eventBus.eventBusName,
+  },
+});
+
+eventBus.grantPutEventsTo(serviceA);
+
+// Service B subscribes to events
+new events.Rule(this, 'ServiceBRule', {
+  eventBus,
+  eventPattern: {
+    source: ['service.a'],
+    detailType: ['EntityCreated'],
+  },
+  targets: [new targets.LambdaFunction(serviceBFunction)],
+});
+
+// Service C subscribes to same events
+new events.Rule(this, 'ServiceCRule', {
+  eventBus,
+  eventPattern: {
+    source: ['service.a'],
+    detailType: ['EntityCreated'],
+  },
+  targets: [new targets.LambdaFunction(serviceCFunction)],
+});
+```
+
+### Pattern: API Gateway + SQS Integration
+
+**Use case**: Async API requests without Lambda
+
+```typescript
+const queue = new sqs.Queue(this, 'RequestQueue');
+
+const api = new apigateway.RestApi(this, 'Api');
+
+// Direct SQS integration (no Lambda)
+const sqsIntegration = new apigateway.AwsIntegration({
+  service: 'sqs',
+  path: `${process.env.AWS_ACCOUNT_ID}/${queue.queueName}`,
+  integrationHttpMethod: 'POST',
+  options: {
+    credentialsRole: sqsRole,
+    requestParameters: {
+      'integration.request.header.Content-Type': "'application/x-www-form-urlencoded'",
+    },
+    requestTemplates: {
+      'application/json': 'Action=SendMessage&MessageBody=$input.body',
+    },
+    integrationResponses: [{
+      statusCode: '200',
+    }],
+  },
+});
+
+api.root.addMethod('POST', sqsIntegration, {
+  methodResponses: [{ statusCode: '200' }],
+});
+```
+
+### Pattern: EventBridge + Step Functions
+
+**Use case**: Event-triggered workflow orchestration
+
+```typescript
+// State machine for order processing
+const orderStateMachine = new stepfunctions.StateMachine(this, 'OrderFlow', {
+  definition: /* ... */,
+});
+
+// EventBridge triggers state machine
+new events.Rule(this, 'OrderPlacedRule', {
+  eventPattern: {
+    source: ['orders'],
+    detailType: ['OrderPlaced'],
+  },
+  targets: [new targets.SfnStateMachine(orderStateMachine)],
+});
+```
+
+## Orchestration Patterns
+
+### Pattern: Sequential Workflow
+
+**Use case**: Multi-step process with dependencies
+
+```typescript
+const definition = new tasks.LambdaInvoke(this, 'Step1', {
+  lambdaFunction: step1Function,
+  outputPath: '$.Payload',
+})
+  .next(new tasks.LambdaInvoke(this, 'Step2', {
+    lambdaFunction: step2Function,
+    outputPath: '$.Payload',
+  }))
+  .next(new tasks.LambdaInvoke(this, 'Step3', {
+    lambdaFunction: step3Function,
+    outputPath: '$.Payload',
+  }));
+
+new stepfunctions.StateMachine(this, 'Sequential', {
+  definition,
+});
+```
+
+### Pattern: Parallel Execution
+
+**Use case**: Execute independent tasks concurrently
+
+```typescript
+const parallel = new stepfunctions.Parallel(this, 'ParallelProcessing');
+
+parallel.branch(new tasks.LambdaInvoke(this, 'ProcessA', {
+  lambdaFunction: functionA,
+}));
+
+parallel.branch(new tasks.LambdaInvoke(this, 'ProcessB', {
+  lambdaFunction: functionB,
+}));
+
+parallel.branch(new tasks.LambdaInvoke(this, 'ProcessC', {
+  lambdaFunction: functionC,
+}));
+
+const definition = parallel.next(new tasks.LambdaInvoke(this, 'Aggregate', {
+  lambdaFunction: aggregateFunction,
+}));
+
+new stepfunctions.StateMachine(this, 'Parallel', { definition });
+```
+
+### Pattern: Map State (Dynamic Parallelism)
+
+**Use case**: Process array of items in parallel
+
+```typescript
+const mapState = new stepfunctions.Map(this, 'ProcessItems', {
+  maxConcurrency: 10,
+  itemsPath: '$.items',
+});
+
+mapState.iterator(new tasks.LambdaInvoke(this, 'ProcessItem', {
+  lambdaFunction: processItemFunction,
+}));
+
+const definition = mapState.next(new tasks.LambdaInvoke(this, 'Finalize', {
+  lambdaFunction: finalizeFunction,
+}));
+```
+
+### Pattern: Choice State (Conditional Logic)
+
+**Use case**: Branching logic based on input
+
+```typescript
+const choice = new stepfunctions.Choice(this, 'OrderType');
+
+choice.when(
+  stepfunctions.Condition.stringEquals('$.orderType', 'STANDARD'),
+  standardProcessing
+);
+
+choice.when(
+  stepfunctions.Condition.stringEquals('$.orderType', 'EXPRESS'),
+  expressProcessing
+);
+
+choice.otherwise(defaultProcessing);
+```
+
+### Pattern: Wait State
+
+**Use case**: Delay between steps or wait for callbacks
+
+```typescript
+// Fixed delay
+const wait = new stepfunctions.Wait(this, 'Wait30Seconds', {
+  time: stepfunctions.WaitTime.duration(Duration.seconds(30)),
+});
+
+// Wait until timestamp
+const waitUntil = new stepfunctions.Wait(this, 'WaitUntil', {
+  time: stepfunctions.WaitTime.timestampPath('$.expiryTime'),
+});
+
+// Wait for callback (.waitForTaskToken)
+const waitForCallback = new tasks.LambdaInvoke(this, 'WaitForApproval', {
+  lambdaFunction: approvalFunction,
+  integrationPattern: stepfunctions.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
+  payload: stepfunctions.TaskInput.fromObject({
+    token: stepfunctions.JsonPath.taskToken,
+    data: stepfunctions.JsonPath.entirePayload,
+  }),
+});
+```
+
+## Anti-Patterns
+
+### ❌ Lambda Monolith
+
+**Problem**: Single Lambda handling all operations
+
+```typescript
+// BAD
+export const handler = async (event: any) => {
+  switch (event.operation) {
+    case 'createUser': return createUser(event);
+    case 'getUser': return getUser(event);
+    case 'updateUser': return updateUser(event);
+    case 'deleteUser': return deleteUser(event);
+    case 'createOrder': return createOrder(event);
+    // ... 20 more operations
+  }
+};
+```
+
+**Solution**: Separate Lambda functions per operation
+
+```typescript
+// GOOD - Separate functions
+export const createUser = async (event: any) => { /* ... */ };
+export const getUser = async (event: any) => { /* ... */ };
+export const updateUser = async (event: any) => { /* ... */ };
+```
+
+### ❌ Recursive Lambda Pattern
+
+**Problem**: Lambda invoking itself (runaway costs)
+
+```typescript
+// BAD
+export const handler = async (event: any) => {
+  await processItem(event);
+
+  if (hasMoreItems()) {
+    await lambda.invoke({
+      FunctionName: process.env.AWS_LAMBDA_FUNCTION_NAME,
+      InvocationType: 'Event',
+      Payload: JSON.stringify({ /* next batch */ }),
+    });
+  }
+};
+```
+
+**Solution**: Use SQS or Step Functions
+
+```typescript
+// GOOD - Use SQS for iteration
+export const handler = async (event: SQSEvent) => {
+  for (const record of event.Records) {
+    await processItem(record);
+  }
+  // SQS handles iteration automatically
+};
+```
+
+### ❌ Lambda Chaining
+
+**Problem**: Lambda directly invoking another Lambda
+
+```typescript
+// BAD
+export const handler1 = async (event: any) => {
+  const result = await processStep1(event);
+
+  // Directly invoking next Lambda
+  await lambda.invoke({
+    FunctionName: 'handler2',
+    Payload: JSON.stringify(result),
+  });
+};
+```
+
+**Solution**: Use EventBridge, SQS, or Step Functions
+
+```typescript
+// GOOD - Publish to EventBridge
+export const handler1 = async (event: any) => {
+  const result = await processStep1(event);
+
+  await eventBridge.putEvents({
+    Entries: [{
+      Source: 'service.step1',
+      DetailType: 'Step1Completed',
+      Detail: JSON.stringify(result),
+    }],
+  });
+};
+```
+
+### ❌ Synchronous Waiting in Lambda
+
+**Problem**: Lambda waiting for slow operations
+
+```typescript
+// BAD - Blocking on slow operation
+export const handler = async (event: any) => {
+  await startBatchJob(); // Returns immediately
+
+  // Wait for job to complete (wastes Lambda time)
+  while (true) {
+    const status = await checkJobStatus();
+    if (status === 'COMPLETE') break;
+    await sleep(1000);
+  }
+};
+```
+
+**Solution**: Use Step Functions with callback pattern
+
+```typescript
+// GOOD - Step Functions waits, not Lambda
+const waitForJob = new tasks.LambdaInvoke(this, 'StartJob', {
+  lambdaFunction: startJobFunction,
+  integrationPattern: stepfunctions.IntegrationPattern.WAIT_FOR_TASK_TOKEN,
+  payload: stepfunctions.TaskInput.fromObject({
+    token: stepfunctions.JsonPath.taskToken,
+  }),
+});
+```
+
+### ❌ Large Deployment Packages
+
+**Problem**: Large Lambda packages increase cold start time
+
+**Solution**:
+- Use layers for shared dependencies
+- Externalize AWS SDK
+- Minimize bundle size
+
+```typescript
+new NodejsFunction(this, 'Function', {
+  entry: 'src/handler.ts',
+  bundling: {
+    minify: true,
+    externalModules: ['@aws-sdk/*'], // Provided by runtime
+    nodeModules: ['only-needed-deps'], // Selective bundling
+  },
+});
+```
+
+## Performance Optimization
+
+### Cold Start Optimization
+
+**Techniques**:
+1. Minimize package size
+2. Use provisioned concurrency for critical paths
+3. Lazy load dependencies
+4. Reuse connections outside handler
+5. Use Lambda SnapStart (Java)
+
+```typescript
+// For latency-sensitive APIs
+const apiFunction = new NodejsFunction(this, 'ApiFunction', {
+  entry: 'src/api.ts',
+  memorySize: 1769, // 1 vCPU for faster initialization
+});
+
+const alias = apiFunction.currentVersion.addAlias('live');
+alias.addAutoScaling({
+  minCapacity: 2,
+  maxCapacity: 10,
+}).scaleOnUtilization({
+  utilizationTarget: 0.7,
+});
+```
+
+### Right-Sizing Memory
+
+**Test different memory configurations**:
+
+```typescript
+// CPU-bound workload
+new NodejsFunction(this, 'ComputeFunction', {
+  memorySize: 1769, // 1 vCPU
+  timeout: Duration.seconds(30),
+});
+
+// I/O-bound workload
+new NodejsFunction(this, 'IOFunction', {
+  memorySize: 512, // Less CPU needed
+  timeout: Duration.seconds(60),
+});
+
+// Simple operations
+new NodejsFunction(this, 'SimpleFunction', {
+  memorySize: 256,
+  timeout: Duration.seconds(10),
+});
+```
+
+### Concurrent Execution Control
+
+```typescript
+// Protect downstream services
+new NodejsFunction(this, 'Function', {
+  reservedConcurrentExecutions: 10, // Max 10 concurrent
+});
+
+// Unreserved concurrency (shared pool)
+new NodejsFunction(this, 'Function', {
+  // Uses unreserved account concurrency
+});
+```
+
+## Testing Strategies
+
+### Unit Testing
+
+Test business logic separate from AWS services:
+
+```typescript
+// handler.ts
+export const processOrder = async (order: Order): Promise<Result> => {
+  // Business logic (easily testable)
+  const validated = validateOrder(order);
+  const priced = calculatePrice(validated);
+  return transformResult(priced);
+};
+
+export const handler = async (event: any): Promise<any> => {
+  const order = parseEvent(event);
+  const result = await processOrder(order);
+  await saveToDatabase(result);
+  return formatResponse(result);
+};
+
+// handler.test.ts
+test('processOrder calculates price correctly', () => {
+  const order = { items: [{ price: 10, quantity: 2 }] };
+  const result = processOrder(order);
+  expect(result.total).toBe(20);
+});
+```
+
+### Integration Testing
+
+Test with actual AWS services:
+
+```typescript
+// integration.test.ts
+import { LambdaClient, InvokeCommand } from '@aws-sdk/client-lambda';
+
+test('Lambda processes order correctly', async () => {
+  const lambda = new LambdaClient({});
+
+  const response = await lambda.send(new InvokeCommand({
+    FunctionName: process.env.FUNCTION_NAME,
+    Payload: JSON.stringify({ orderId: '123' }),
+  }));
+
+  const result = JSON.parse(Buffer.from(response.Payload!).toString());
+  expect(result.statusCode).toBe(200);
+});
+```
+
+### Local Testing with SAM
+
+```bash
+# Test API locally
+sam local start-api
+
+# Invoke function locally
+sam local invoke MyFunction -e events/test-event.json
+
+# Generate sample event
+sam local generate-event apigateway aws-proxy > event.json
+```
+
+## Summary
+
+- **Single Purpose**: One function, one responsibility
+- **Concurrent Design**: Think concurrency, not volume
+- **Stateless**: Use external storage for state
+- **State Machines**: Orchestrate with Step Functions
+- **Event-Driven**: Use events over direct calls
+- **Idempotent**: Handle failures and duplicates gracefully
+- **Observability**: Enable tracing and structured logging