CDK部署TypeScript Lambda报错：无法找到模块'index'

测试Lambda时出现以下错误：

{
  "errorType": "Runtime.ImportModuleError",
  "errorMessage": "Error: Cannot find module 'index'\nRequire stack:\n- /var/runtime/index.mjs",
  "trace": [
    "Runtime.ImportModuleError: Error: Cannot find module 'index'",
    "Require stack:",
    "- /var/runtime/index.mjs",
    "    at _loadUserApp (file:///var/runtime/index.mjs:996:17)",
    "    at async UserFunction.js.module.exports.load (file:///var/runtime/index.mjs:1031:21)",
    "    at async start (file:///var/runtime/index.mjs:1194:23)",
    "    at async file:///var/runtime/index.mjs:1200:1"
  ]
}

Lambda在CDK中的定义：

const postImages = new lambda.Function(scope, utils.prefixed('post_images'), {
    runtime: lambda.Runtime.NODEJS_18_X,
    handler: 'index.lambdaHandler',
    code: lambda.Code.fromAsset('./sd_service/post_images')
})

./sd_service/post_images目录包含以下文件：

index.ts #

import { Context, APIGatewayEvent, APIGatewayProxyResult } from 'aws-lambda';

export const lambdaHandler = async (event: APIGatewayEvent, context: Context): Promise<APIGatewayProxyResult> => {
    console.log(`Event: ${JSON.stringify(event, null, 2)}`);
    console.log(`Context: ${JSON.stringify(context, null, 2)}`);
    return {
        statusCode: 200,
        body: JSON.stringify({
            message: 'hello world',
        }),
    };
};

tsconfig.json #

{
    "$schema": "https://json.schemastore.org/tsconfig",
    "display": "Node 18",
    "compilerOptions": {
        "lib": ["es2022"],
        "module": "commonjs",
        "target": "es2022",
        "strict": true,
        "esModuleInterop": true,
        "skipLibCheck": true,
        "forceConsistentCasingInFileNames": true,
        "moduleResolution": "node"
    },
    "exclude": ["node_modules", "**/*.test.ts"]
}

package.json #

{
  "name": "post_images",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "author": "",
  "license": "ISC",
  "devDependencies": {
    "@types/aws-lambda": "^8.10.111",
    "@types/node": "^18.14.6",
    "aws-sdk": "^2.1330.0",
    "typescript": "^4.9.5"
  },
  "dependencies": {
    "aws-lambda": "^1.0.7"
  }
}

原因 #

Lambda运行环境（Node.js）只能执行JavaScript文件，你当前直接将TypeScript源码目录作为部署资产，CDK的lambda.Code.fromAsset不会自动编译TypeScript，导致部署到Lambda的是.ts文件而非.js文件，运行时找不到index.js模块。

解决方案 #

方案1：手动编译TypeScript后部署 #

1. 修改tsconfig.json，添加输出目录配置，将编译后的JS文件输出到dist目录：

   {
       "compilerOptions": {
           // 保留原有配置
           "outDir": "./dist"
       }
   }
   

2. 修改package.json，添加编译脚本：

   {
       "scripts": {
           "build": "tsc",
           "test": "echo \"Error: no test specified\" && exit 1"
       }
   }
   

3. 执行编译：在./sd_service/post_images目录下运行命令：

   npm run build
   

4. 修改CDK代码，将资产路径指向编译后的dist目录：

   const postImages = new lambda.Function(scope, utils.prefixed('post_images'), {
       runtime: lambda.Runtime.NODEJS_18_X,
       handler: 'index.lambdaHandler',
       code: lambda.Code.fromAsset('./sd_service/post_images/dist')
   })
   

5. 重新部署CDK栈即可。

方案2：使用CDK的NodejsFunction自动处理编译 #

使用AWS CDK提供的lambda.NodejsFunction构造，它会自动完成TypeScript编译、依赖打包等操作，无需手动处理：

1. 修改CDK代码：

   import { NodejsFunction } from 'aws-cdk-lib/aws-lambda-nodejs';
   
   const postImages = new NodejsFunction(scope, utils.prefixed('post_images'), {
       runtime: lambda.Runtime.NODEJS_18_X,
       handler: 'lambdaHandler',
       entry: './sd_service/post_images/index.ts'
   })
   

2. 直接重新部署CDK栈即可。

内容的提问来源于stack exchange，提问作者sak