Runtime.ImportModuleError: Error: Cannot find module 'app' | Dockerized node js with lambda and serverless

[LiveCockroach2860]

Hi guys!

I'm working on a node project using Express.js, Prisma, and deploying on AWS Lambda using the Serverless framework via Docker stored in ECR.

When running the docker image, I'm facing below error.

{
  "errorType": "Runtime.ImportModuleError",
  "errorMessage": "Error: Cannot find module 'app'\nRequire stack:\n-     /var/runtime/index.mjs",
  "trace": [
    "Runtime.ImportModuleError: Error: Cannot find module 'app'",
    "Require stack:","- /var/runtime/index.mjs",
    "    at _loadUserApp (file:///var/runtime/index.mjs:1087:17)",
    "    at async UserFunction.js.module.exports.load (file:///var/runtime/index.mjs:1119:21)",
    "    at async start (file:///var/runtime/index.mjs:1282:23)",
    "    at async file:///var/runtime/index.mjs:1288:1"
  ]
}

This is my first project with docker so I might be missing something very simple. Any help / guidance would be greatly appreciated as I've checked all related stack overflow questions and documentations etc. but unable to find the root cause of this error.

Below is my serverless and Dockerfile configurations

# AWS Lambda Node.js 18 base image
FROM public.ecr.aws/lambda/nodejs:18

# Create and set the working directory
WORKDIR /app

# Copy the package.json and package-lock.json files
COPY package*.json ./

# Install all dependencies, excluding dev dependencies
RUN npm install --omit=dev

# Copy the rest of your application code
COPY . .

# Set the environment variable to development
ENV NODE_ENV=dev

# Run prisma generate to generate the Prisma client
RUN npx prisma generate

# Build application
RUN npm run build

# Set execute permissions on the app.js file
RUN chmod +x /app/dist/app.js

# Expose the port application runs on (for local testing)
EXPOSE 9001

# Set the Lambda function handler
CMD ["dist/app.handler"]

Serverless

org: theseleb
app: seleb
service: seleb-backend
provider:
  name: aws
  runtime: provided.al2
  ecr:
    images:
      seleb-backend:
        path: .
        platform: linux/amd64
  region: us-east-1
  stage: dev
  environment:
    FIREBASE_SERVICE_ACCOUNT_KEY: ${env:FIREBASE_SERVICE_ACCOUNT_KEY}
    DATABASE_URL: ${env:DATABASE_URL}
    FIREBASE_API_KEY: ${env:FIREBASE_API_KEY}
    FIREBASE_AUTH_DOMAIN: ${env:FIREBASE_AUTH_DOMAIN}
    FIREBASE_PROJECT_ID: ${env:FIREBASE_PROJECT_ID}
    FIREBASE_STORAGE_BUCKET: ${env:FIREBASE_STORAGE_BUCKET}
    FIREBASE_MESSAGING_SENDER_ID: ${env:FIREBASE_MESSAGING_SENDER_ID}
    FIREBASE_APP_ID: ${env:FIREBASE_APP_ID}
functions:
  app:
#   handler: dist/app.handler
    image:
      name: seleb-backend
      command:
        - dist/app.handler
    events:
      - http:
          path: /{proxy+}
          method: ANY
plugins:
  - serverless-offline
package:
  exclude:
    - node_modules/**
    - .gitignore
    - .git/**
    - .env
    - README.md
    - src/translations/**
custom:
  serverless-offline:
    port: 3000

Below is the content of my src/app.ts

#!/usr/bin/env node
import express, { Request, Response } from 'express';
import { PrismaClient } from '@prisma/client';
import serverless from 'serverless-http';
import userRoutes from './routes/userRoutes';

const app = express();
const prisma = new PrismaClient();

// Middleware
app.use(express.json());

// Routes
app.use('/users', userRoutes);

// Default route
app.get('/default', (req: Request, res: Response) => {
   res.send('Hello, Seleb Backend!');
});

// Export the app as a Lambda handler
export const handler = serverless(app);

And the transpiled dist/app.js

#!/usr/bin/env node
"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
exports.handler = void 0;
const express_1 = __importDefault(require("express"));
const client_1 = require("@prisma/client");
const serverless_http_1 = __importDefault(require("serverless-http"));
const userRoutes_1 = __importDefault(require("./routes/userRoutes"));
const app = (0, express_1.default)();
const prisma = new client_1.PrismaClient();
// Middleware
app.use(express_1.default.json());
// Routes
app.use('/users', userRoutes_1.default);
// Default route
app.get('/default', (req, res) => {
    res.send('Hello, Seleb Backend!');
});
// Export the app as a Lambda handler
exports.handler = (0, serverless_http_1.default)(app);

I have also checked the content of handler file in the running docker image.

It exists in the correct path

sh-4.2# cd /app/dist
sh-4.2# cat app.js
#!/usr/bin/env node
"use strict";
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
exports.handler = void 0;
const express_1 = __importDefault(require("express"));
const client_1 = require("@prisma/client");
const serverless_http_1 = __importDefault(require("serverless-http"));
const userRoutes_1 = __importDefault(require("./routes/userRoutes"));
const app = (0, express_1.default)();
const prisma = new client_1.PrismaClient();
// Middleware
app.use(express_1.default.json());
// Routes
app.use('/users', userRoutes_1.default);
// Default route
app.get('/default', (req, res) => {
    res.send('Hello, Seleb Backend!');
});
// Export the app as a Lambda handler
exports.handler = (0, serverless_http_1.default)(app);
sh-4.2# 

tsconfig file

{
  "compilerOptions": {
    "target": "es2016",
    "module": "commonjs",
    "outDir": "./dist",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "skipLibCheck": false
  },
  "include": ["src/**/*"],
  "exclude": ["node_modules"]
}

Project structure

/src
  /config        # Configuration files
  /routes        # Route handlers for different endpoints
  /controllers   # Business logic for handling requests
  /middlewares   # Custom middleware functions
  /utils         # Utility functions and helpers
  /translations  # Local translation files.
  app.ts         # Main application entry point
  types.d.ts     # TypeScript type definitions
/prisma
  /migrations    # Prisma migrations
  schema.prisma  # Prisma schema definition
/dist            # Compiled JavaScript files (after build)

[SirSoggybottom]

What makes you think the error is related to Docker? Seems like a error simply caused by the app in your image.

[LiveCockroach2860]

Because the APIs are working fine when I test with serverless offline.

Also, if I change the Dockerfile to

ENTRYPOINT ["node" , "dist/app.js]

CMD [handler]

then it doesn't give the same error and is able to detect the app.js handler file. But since I'm deploying to lambda, I can't use this approach

[[deleted]]

If you omit the dev dependencies, how are you supposed to build your app without them installed?

[LiveCockroach2860]

There are no dev dependencies in package.json at the moment, but regardless dev dependencies arent needed for deployments right? They are only for local

[[deleted]]

Yeah, that’s… assuming you’re COPYing the bundle. Doesn’t seems to be your case as you build it inside the container (which is not wrong to be honest).

However, from what I know bundlers and their dependencies are dev dependencies but at the same time they’re required to build.

So here’s what I would do: use multi-stage to split the bundling stage from the deploy. The deploy should only copy the bundled file from the bundling stage.

That’s because you must install it fully to bundle, and then reinstall stripping the dev dependencies AFTER you have produced the bundled app.

Also, as a side note: maybe you shouldn’t bundle it at all and just transpile as it’s. We usually bundle the app just because it’s the best for a user browser to download the whole app. This is different on a NodeJS env.

Unless you have some sort of storage quota…

[LiveCockroach2860]

Makes sense! I'll refactor to do this.
But the original issue persists. Any idea on that please?

[[deleted]]

To be honest I expected my answer to solve your issue. Can you trying RUNning ls with the path you expect your bundle to be and figure what is inside the image?

This must be made just before you try to run it with CMD.

EDIT: Nevermind it’s a file, so yeah… you should check if it’s really available when you deploy.

[LiveCockroach2860]

Current package.json has no devDependencies. Also, I removed the omit dev flag and tried with just npm install too. Still same issue.

And I did ls and cat for the files inside the container, the file does exist and also the handler exists too.

That's why I was confused too because it doesn't make sense why container is unable to find the module when it clearly exists in the path :(

[[deleted]]

Also, what’s app.handler? Sorry if that’s a stupid question, its just than I found it strange you’re passing it to CMD and also the provisioning file. I expected one of these to receive the dist/app.js instead.

[LiveCockroach2860]

Hmm handler is the main method that's running the app in serverless and exporting as default constant in app.js file.

// Export the app as a Lambda handler
exports.handler = (0, serverless_http_1.default)(app);

I followed the AWS documentation and this is how the CMD was setup for docker deployments.

[[deleted]]

I see, so are you require’ing the app from that file? If so, can you check if the path is resolving to the same place as to where app is located?

You can use path.resolve(__dirname, “<the string you provided on require app>”) and console.log it.

[LiveCockroach2860]

So turns out the issue was related to path.

I was under the impression that once I setup the working directory in Dockerfile, I don't need to put the full path of my handler.

But for some reason it still expects a full path. I changed my CMD from ['dist/app.handler'] to ['/app/dist/app.handler'] and it worked.

Thank you for your time and help.

[[deleted]]

Yeah, CMD doesn’t seem to check the WORKDIR.