AWS Lambda Typescript Integration

my-nestjs-lambda/
├── src/
│   ├── app.module.ts
│   ├── main.ts
│   ├── lambda.ts           # Lambda entry point
│   └── modules/
│       └── api/
├── package.json
├── tsconfig.json
└── serverless.yml

my-ts-lambda/
├── src/
│   ├── handlers/
│   │   └── api.handler.ts
│   ├── services/
│   └── utils/
├── dist/                   # Compiled output
├── package.json
├── tsconfig.json
└── template.yaml

// lambda.ts
import { NestFactory } from '@nestjs/core';
import { ExpressAdapter } from '@nestjs/platform-express';
import serverlessExpress from '@codegenie/serverless-express';
import { Context, Handler } from 'aws-lambda';
import express from 'express';
import { AppModule } from './src/app.module';

let cachedServer: Handler;

async function bootstrap(): Promise<Handler> {
  const expressApp = express();
  const adapter = new ExpressAdapter(expressApp);
  const nestApp = await NestFactory.create(AppModule, adapter);
  await nestApp.init();
  return serverlessExpress({ app: expressApp });
}

export const handler: Handler = async (event: any, context: Context) => {
  if (!cachedServer) {
    cachedServer = await bootstrap();
  }
  return cachedServer(event, context);
};

// src/handlers/api.handler.ts
import { APIGatewayProxyEvent, APIGatewayProxyResult, Context } from 'aws-lambda';

export const handler = async (
  event: APIGatewayProxyEvent,
  context: Context
): Promise<APIGatewayProxyResult> => {
  return {
    statusCode: 200,
    headers: { 'Content-Type': 'application/json' },
    body: JSON.stringify({ message: 'Hello from TypeScript Lambda!' })
  };
};

// GOOD: Initialize once, reuse across invocations
import { DynamoDBClient } from '@aws-sdk/client-dynamodb';

const dynamoClient = new DynamoDBClient({ region: process.env.AWS_REGION });

export const handler = async (event: APIGatewayProxyEvent) => {
  // Use dynamoClient - already initialized
};

// src/config/env.config.ts
export const env = {
  region: process.env.AWS_REGION || 'us-east-1',
  tableName: process.env.TABLE_NAME || '',
  debug: process.env.DEBUG === 'true',
};

// Validate required variables
if (!env.tableName) {
  throw new Error('TABLE_NAME environment variable is required');
}

{
  "dependencies": {
    "aws-lambda": "^3.1.0",
    "@aws-sdk/client-dynamodb": "^3.450.0"
  },
  "devDependencies": {
    "typescript": "^5.3.0",
    "esbuild": "^0.19.0"
  }
}

export const handler = async (event: APIGatewayProxyEvent): Promise<APIGatewayProxyResult> => {
  try {
    const result = await processEvent(event);
    return {
      statusCode: 200,
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify(result)
    };
  } catch (error) {
    console.error('Error processing request:', error);
    return {
      statusCode: 500,
      headers: { 'Content-Type': 'application/json' },
      body: JSON.stringify({ error: 'Internal server error' })
    };
  }
};

const log = (level: string, message: string, meta?: object) => {
  console.log(JSON.stringify({
    level,
    message,
    timestamp: new Date().toISOString(),
    ...meta
  }));
};

log('info', 'Request processed', { requestId: context.awsRequestId });

service: my-typescript-api

provider:
  name: aws
  runtime: nodejs20.x

functions:
  api:
    handler: dist/handler.handler
    events:
      - http:
          path: /{proxy+}
          method: ANY

AWSTemplateFormatVersion: '2010-09-09'
Transform: AWS::Serverless-2016-10-31

Resources:
  ApiFunction:
    Type: AWS::Serverless::Function
    Properties:
      CodeUri: dist/
      Handler: handler.handler
      Runtime: nodejs20.x
      Events:
        ApiEvent:
          Type: Api
          Properties:
            Path: /{proxy+}
            Method: ANY