New pattern - lambda-az-aware-routing-cdk

lambda-az-aware-routing-cdk/README.md

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+# AWS Lambda AZ-aware routing with metadata endpoint
+
+This pattern deploys a Lambda function that uses the new Lambda metadata endpoint to discover its Availability Zone ID and demonstrates same-AZ routing to reduce cross-AZ latency and data transfer costs.
+
+Learn more about this pattern at Serverless Land Patterns: https://serverlessland.com/patterns/lambda-az-aware-routing-cdk
+
+Important: this application uses various AWS services and there are costs associated with these services after the Free Tier usage - please see the [AWS Pricing page](https://aws.amazon.com/pricing/) for details. You are responsible for any AWS costs incurred. No warranty is implied in this example.
+
+## Requirements
+
+* [Create an AWS account](https://portal.aws.amazon.com/gp/aws/developer/registration/index.html) if you do not already have one and log in. The IAM user that you use must have sufficient permissions to make necessary AWS service calls and manage AWS resources.
+* [AWS CLI](https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2.html) installed and configured
+* [Git Installed](https://git-scm.com/book/en/v2/Getting-Started-Installing-Git)
+* [Node and NPM](https://nodejs.org/en/download/) installed
+* [AWS CDK](https://docs.aws.amazon.com/cdk/latest/guide/cli.html) installed
+
+## How it works
+
+![Architecture](architecture.png)
+
+1. A client invokes the Lambda function.
+2. The function calls the Lambda metadata endpoint (`http://${AWS_LAMBDA_METADATA_API}/2026-01-15/metadata/execution-environment`) using the `AWS_LAMBDA_METADATA_TOKEN` for authentication.
+3. The endpoint returns the AZ ID (e.g., `use1-az1`) — a consistent identifier across all AWS accounts.
+4. The function uses the AZ ID to make routing decisions, such as selecting same-AZ endpoints for ElastiCache, RDS, or DynamoDB DAX.
+5. Same-AZ routing eliminates cross-AZ data transfer costs (~$0.01/GB) and reduces latency by ~1ms per hop.
+
+## Deployment
+
+1. Clone the repository and navigate to the pattern directory:
+    ```bash
+    git clone https://github.com/aws-samples/serverless-patterns
+    cd serverless-patterns/lambda-az-aware-routing-cdk
+    ```
+
+2. Install dependencies:
+    ```bash
+    npm install
+    ```
+
+3. Deploy the stack:
+    ```bash
+    cdk deploy
+    ```
+
+## Testing
+
+Invoke the function multiple times to see different AZ assignments:
+
+```bash
+FUNCTION_NAME=$(aws cloudformation describe-stacks \
+  --stack-name LambdaAzAwareRoutingStack \
+  --query 'Stacks[0].Outputs[?OutputKey==`FunctionName`].OutputValue' \
+  --output text)
+
+# Invoke 5 times to see AZ distribution
+for i in {1..5}; do
+  aws lambda invoke --function-name $FUNCTION_NAME --payload '{}' /dev/stdout 2>/dev/null | python3 -m json.tool
+  echo "---"
+done
+```
+
+Expected output: Each invocation returns the AZ ID where the function is running (e.g., `use1-az1`, `use1-az2`).
+
+## Cleanup
+
+```bash
+cdk destroy
+```
+
+----
+Copyright 2026 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+
+SPDX-License-Identifier: MIT-0

lambda-az-aware-routing-cdk/bin/app.ts

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+#!/usr/bin/env node
+import "source-map-support/register";
+import * as cdk from "aws-cdk-lib";
+import { LambdaAzAwareRoutingStack } from "../lib/lambda-az-aware-routing-stack";
+
+const app = new cdk.App();
+new LambdaAzAwareRoutingStack(app, "LambdaAzAwareRoutingStack", {
+  env: {
+    account: process.env.CDK_DEFAULT_ACCOUNT,
+    region: process.env.CDK_DEFAULT_REGION,
+  },
+});

lambda-az-aware-routing-cdk/cdk.json

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+{
+  "app": "npx ts-node --prefer-ts-exts bin/app.ts"
+}

lambda-az-aware-routing-cdk/example-pattern.json

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+{
+  "title": "AWS Lambda AZ-aware routing with metadata endpoint",
+  "description": "Deploy a Lambda function that reads its Availability Zone ID from the new metadata endpoint and demonstrates same-AZ routing to reduce cross-AZ latency.",
+  "language": "TypeScript",
+  "level": "300",
+  "framework": "AWS CDK",
+  "services": {
+    "from": "lambda",
+    "to": "dynamodb"
+  },
+  "introBox": {
+    "headline": "How it works",
+    "text": [
+      "This pattern deploys a Lambda function that uses the new Lambda metadata endpoint (March 2026) to discover which Availability Zone it is running in. The function reads the AZ ID (e.g., use1-az1) and demonstrates how to use it for same-AZ routing decisions.",
+      "Same-AZ routing eliminates cross-AZ data transfer costs and reduces latency by approximately 1ms per hop. This is valuable for latency-sensitive workloads that call downstream services like ElastiCache, RDS, or DynamoDB DAX."
+    ]
+  },
+  "gitHub": {
+    "template": {
+      "repoURL": "https://github.com/aws-samples/serverless-patterns/tree/main/lambda-az-aware-routing-cdk",
+      "templateURL": "serverless-patterns/lambda-az-aware-routing-cdk",
+      "projectFolder": "lambda-az-aware-routing-cdk",
+      "templateFile": "lib/lambda-az-aware-routing-stack.ts"
+    }
+  },
+  "resources": {
+    "bullets": [
+      { "text": "Lambda AZ metadata announcement", "link": "https://aws.amazon.com/about-aws/whats-new/2026/03/lambda-availability-zone-metadata/" },
+      { "text": "Using the Lambda metadata endpoint", "link": "https://docs.aws.amazon.com/lambda/latest/dg/configuration-metadata-endpoint.html" },
+      { "text": "AZ IDs for cross-account consistency", "link": "https://docs.aws.amazon.com/global-infrastructure/latest/regions/az-ids.html" }
+    ]
+  },
+  "deploy": {
+    "text": ["cdk deploy"],
+    "file": "lib/lambda-az-aware-routing-stack.ts"
+  },
+  "testing": {
+    "text": ["See the README for testing instructions."]
+  },
+  "cleanup": {
+    "text": ["cdk destroy"]
+  },
+  "authors": [
+    {
+      "name": "Nithin Chandran R",
+      "bio": "Technical Account Manager at AWS",
+      "linkedin": "nithin-chandran-r"
+    }
+  ]
+}

lambda-az-aware-routing-cdk/lib/lambda-az-aware-routing-stack.ts

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+import * as cdk from "aws-cdk-lib";
+import * as dynamodb from "aws-cdk-lib/aws-dynamodb";
+import * as lambda from "aws-cdk-lib/aws-lambda";
+import * as nodejs from "aws-cdk-lib/aws-lambda-nodejs";
+import { Construct } from "constructs";
+
+export class LambdaAzAwareRoutingStack extends cdk.Stack {
+  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
+    super(scope, id, props);
+
+    // DynamoDB table to record AZ routing decisions
+    const table = new dynamodb.Table(this, "AzRoutingTable", {
+      partitionKey: { name: "pk", type: dynamodb.AttributeType.STRING },
+      sortKey: { name: "sk", type: dynamodb.AttributeType.STRING },
+      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
+      removalPolicy: cdk.RemovalPolicy.DESTROY,
+    });
+
+    // Lambda function that reads AZ metadata and demonstrates routing
+    const routerFn = new nodejs.NodejsFunction(this, "AzRouterFn", {
+      entry: "src/az-router/index.ts",
+      handler: "handler",
+      runtime: lambda.Runtime.NODEJS_22_X,
+      timeout: cdk.Duration.seconds(30),
+      memorySize: 256,
+      environment: {
+        TABLE_NAME: table.tableName,
+      },
+      bundling: {
+        minify: true,
+        sourceMap: true,
+      },
+      description:
+        "Reads Lambda AZ metadata and demonstrates same-AZ routing",
+    });
+
+    table.grantWriteData(routerFn);
+
+    // Function URL for easy testing
+    const fnUrl = routerFn.addFunctionUrl({
+      authType: lambda.FunctionUrlAuthType.AWS_IAM,
+    });
+
+    new cdk.CfnOutput(this, "FunctionName", {
+      value: routerFn.functionName,
+    });
+    new cdk.CfnOutput(this, "FunctionUrl", {
+      value: fnUrl.url,
+    });
+    new cdk.CfnOutput(this, "TableName", {
+      value: table.tableName,
+    });
+  }
+}

lambda-az-aware-routing-cdk/package.json

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+{
+  "name": "lambda-az-aware-routing-cdk",
+  "version": "1.0.0",
+  "bin": { "app": "bin/app.ts" },
+  "scripts": { "build": "tsc", "cdk": "cdk" },
+  "dependencies": {
+    "aws-cdk-lib": "^2.180.0",
+    "constructs": "^10.4.2"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "ts-node": "^10.9.0",
+    "typescript": "~5.7.0"
+  }
+}

lambda-az-aware-routing-cdk/src/az-router/index.ts

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+/**
+ * Lambda AZ-aware routing — reads AZ metadata from the Lambda metadata endpoint
+ * and demonstrates same-AZ routing by writing the AZ info to DynamoDB.
+ */
+
+import http from "http";
+
+const METADATA_API = process.env.AWS_LAMBDA_METADATA_API;
+const METADATA_TOKEN = process.env.AWS_LAMBDA_METADATA_TOKEN;
+
+interface MetadataResponse {
+  AvailabilityZoneID: string;
+}
+
+let cachedAzId: string | null = null;
+
+async function getAzId(): Promise<string> {
+  if (cachedAzId) return cachedAzId;
+
+  return new Promise((resolve, reject) => {
+    const url = `http://${METADATA_API}/2026-01-15/metadata/execution-environment`;
+    const req = http.get(url, { headers: { Authorization: `Bearer ${METADATA_TOKEN}` } }, (res) => {
+      let data = "";
+      res.on("data", (chunk) => (data += chunk));
+      res.on("end", () => {
+        const parsed: MetadataResponse = JSON.parse(data);
+        cachedAzId = parsed.AvailabilityZoneID;
+        resolve(cachedAzId!);
+      });
+    });
+    req.on("error", reject);
+    req.end();
+  });
+}
+
+// Fallback for local testing where metadata endpoint is unavailable
+async function getAzIdSafe(): Promise<string> {
+  if (!METADATA_API || !METADATA_TOKEN) return "local-dev";
+  try {
+    return await getAzId();
+  } catch {
+    return "unknown";
+  }
+}
+
+export const handler = async (event: any) => {
+  const azId = await getAzIdSafe();
+  const requestId = event.requestContext?.requestId ?? "direct-invoke";
+
+  // In production, use azId to select same-AZ endpoints:
+  // - ElastiCache: pick the reader endpoint in the same AZ
+  // - RDS: pick the reader in the same AZ
+  // - DynamoDB DAX: pick the same-AZ DAX node
+  // This demo logs the AZ and returns it.
+
+  const result = {
+    azId,
+    functionName: process.env.AWS_LAMBDA_FUNCTION_NAME,
+    region: process.env.AWS_REGION,
+    message: `Lambda running in ${azId}. Use this to route to same-AZ downstream services.`,
+    routingExample: {
+      description: "In production, map AZ IDs to same-AZ endpoints",
+      sameAzBenefit: "Eliminates cross-AZ data transfer costs and reduces latency by ~1ms",
+    },
+  };
+
+  return { statusCode: 200, body: JSON.stringify(result) };
+};

lambda-az-aware-routing-cdk/tsconfig.json

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+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "commonjs",
+    "lib": ["es2020"],
+    "declaration": true,
+    "strict": true,
+    "noImplicitAny": true,
+    "strictNullChecks": true,
+    "noImplicitThis": true,
+    "alwaysStrict": true,
+    "outDir": "build",
+    "rootDir": ".",
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "esModuleInterop": true
+  },
+  "exclude": ["node_modules", "build"]
+}