AWS cloud patterns for Lambda, ECS, S3, DynamoDB, and Infrastructure as Code with CDK/Terraform

AWS Cloud Patterns

Lambda Function Pattern

import { APIGatewayProxyHandlerV2 } from "aws-lambda";
import { DynamoDBClient } from "@aws-sdk/client-dynamodb";
import { DynamoDBDocumentClient, GetCommand } from "@aws-sdk/lib-dynamodb";

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

export const handler: APIGatewayProxyHandlerV2 = async (event) => {
  const id = event.pathParameters?.id;
  if (!id) {
    return { statusCode: 400, body: JSON.stringify({ error: "Missing id" }) };
  }

  const result = await client.send(
    new GetCommand({ TableName: process.env.TABLE_NAME!, Key: { pk: id } })
  );

  if (!result.Item) {
    return { statusCode: 404, body: JSON.stringify({ error: "Not found" }) };
  }

  return {
    statusCode: 200,
    headers: { "Content-Type": "application/json" },
    body: JSON.stringify(result.Item),
  };
};

Initialize SDK clients outside the handler to reuse connections across invocations.

DynamoDB Single-Table Design

interface OrderItem {
  pk: string;          // USER#<userId>
  sk: string;          // ORDER#<orderId>
  gsi1pk: string;      // ORDER#<orderId>
  gsi1sk: string;      // ITEM#<itemId>
  entityType: string;  // "Order" | "OrderItem"
  data: Record<string, any>;
  ttl?: number;
}

const params = {
  TableName: "AppTable",
  KeyConditionExpression: "pk = :pk AND begins_with(sk, :prefix)",
  ExpressionAttributeValues: {
    ":pk": `USER#${userId}`,
    ":prefix": "ORDER#",
  },
};

Design access patterns first, then model keys. Use GSIs for alternative query patterns.

CDK Infrastructure

import * as cdk from "aws-cdk-lib";
import { Construct } from "constructs";
import * as lambda from "aws-cdk-lib/aws-lambda-nodejs";
import * as dynamodb from "aws-cdk-lib/aws-dynamodb";
import * as apigateway from "aws-cdk-lib/aws-apigatewayv2";

export class ApiStack extends cdk.Stack {
  constructor(scope: Construct, id: string, props?: cdk.StackProps) {
    super(scope, id, props);

    const table = new dynamodb.Table(this, "AppTable", {
      partitionKey: { name: "pk", type: dynamodb.AttributeType.STRING },
      sortKey: { name: "sk", type: dynamodb.AttributeType.STRING },
      billingMode: dynamodb.BillingMode.PAY_PER_REQUEST,
      pointInTimeRecovery: true,
      removalPolicy: cdk.RemovalPolicy.RETAIN,
    });

    const fn = new lambda.NodejsFunction(this, "ApiHandler", {
      entry: "src/handler.ts",
      runtime: cdk.aws_lambda.Runtime.NODEJS_22_X,
      architecture: cdk.aws_lambda.Architecture.ARM_64,
      memorySize: 256,
      timeout: cdk.Duration.seconds(10),
      environment: { TABLE_NAME: table.tableName },
    });

    table.grantReadWriteData(fn);
  }
}

S3 Event Processing

import { S3Event } from "aws-lambda";
import { S3Client, GetObjectCommand } from "@aws-sdk/client-s3";

const s3 = new S3Client({});

export async function handler(event: S3Event) {
  for (const record of event.Records) {
    const bucket = record.s3.bucket.name;
    const key = decodeURIComponent(record.s3.object.key.replace(/\+/g, " "));

    const obj = await s3.send(new GetObjectCommand({ Bucket: bucket, Key: key }));
    const body = await obj.Body?.transformToString();

    await processFile(key, body);
  }
}

Anti-Patterns

Hardcoding AWS credentials instead of using IAM roles
Not setting Lambda timeout and memory appropriately
Using SELECT * equivalent scans on DynamoDB instead of query with key conditions
Creating one Lambda per CRUD operation instead of grouping by domain
Missing CloudWatch alarms for error rates and throttling
Not enabling point-in-time recovery on DynamoDB tables

Checklist

SDK clients initialized outside Lambda handler
IAM roles follow least-privilege principle
DynamoDB access patterns designed before table schema
Lambda uses ARM64 architecture for cost savings
S3 buckets have versioning and lifecycle policies
CloudWatch alarms set for Lambda errors, duration, and throttles
Infrastructure defined as code (CDK or Terraform)
Secrets stored in Systems Manager Parameter Store or Secrets Manager

Aws Cloud Patterns (skill)

AWS Cloud Patterns

Lambda Function Pattern

DynamoDB Single-Table Design

CDK Infrastructure

S3 Event Processing

Anti-Patterns

Checklist