webpack - __webpack_require__ Module not found on the deployment server

Question

I am trying to use webpack to bundle my application through teamcity and deploy it on a remote server. I was able to achieve it as well, but on the final step of running the application using 'node ./dist/main' I am getting the below error.

PS C:engage-analytics> node .distmain.js
node:internal/modules/cjs/loader:928
throw err;
^

Error: Cannot find module '@nestjs/core'
Require stack:
- C:engage-analyticsdistmain.js
 at Function.Module._resolveFilename (node:internal/modules/cjs/loader:925:15)
 at Function.Module._load (node:internal/modules/cjs/loader:769:27)
 at Module.require (node:internal/modules/cjs/loader:997:19)
 at require (node:internal/modules/cjs/helpers:92:18)
 at Object.@nestjs/core (C:engage-analyticsdistmain.js:181:18)
 at __webpack_require__ (C:engage-analyticsdistmain.js:229:32)
 at fn (C:engage-analyticsdistmain.js:331:21)
 at eval (webpack://nestjs-intro/./src/main.ts?:3:16)
 at Object../src/main.ts (C:engage-analyticsdistmain.js:52:1)
 at __webpack_require__ (C:engage-analyticsdistmain.js:229:32) {
code: 'MODULE_NOT_FOUND',
requireStack: [ 'C:\engage-analytics\dist\main.js' ]
}

PS C:engage-analytics> webpack -v
webpack 5.18.0
webpack-cli 4.4.0

PS C:engage-analytics> node -v
v15.5.1

When I run the same command on the teamcity work directory I am able to start the application. After build I have simply copied the contents of dist to remote server. Here is the package.json, I am executing the highlighted scripts through npm on teamcity server.

package.json

{
name: "nestjs-intro",
version: "0.0.1",
description: "<p align="center"> <a href="http://nestjs.com/" target="blank"><img src="https://nestjs.com/img/logo_text.svg" width="320" alt="Nest Logo" /></a> </p>",
author: "",
private: true,
license: "UNLICENSED",
scripts: {
prebuild: "rimraf dist",
**build**: "npm install && npx webpack",
format: "prettier --write "src/**/*.ts" "test/**/*.ts"",
start: "nest start",
start:dev: "nest start --watch",
start:debug: "nest start --debug --watch",
**start:prod**: "node dist/main",
lint: "eslint "{src,apps,libs,test}/**/*.ts" --fix",
test: "jest",
test:watch: "jest --watch",
test:cov: "jest --coverage",
test:debug: "node --inspect-brk -r tsconfig-paths/register -r ts-node/register node_modules/.bin/jest --runInBand",
test:e2e: "jest --config ./test/jest-e2e.json"
},
dependencies: {
@nestjs/common: "^7.6.5",
@nestjs/core: "^7.5.1",
@nestjs/mongoose: "^7.2.2",
mongoose: "^5.11.3",
reflect-metadata: "^0.1.13",
@nestjs/platform-express: "^7.6.5",
rxjs: "^6.6.3"
},
devDependencies: {
@nestjs/cli: "^7.5.1",
@nestjs/schematics: "^7.1.3",
@nestjs/testing: "^7.5.1",
@types/express: "^4.17.8",
@types/jest: "^26.0.15",
@types/node: "^14.14.6",
@types/supertest: "^2.0.10",
@typescript-eslint/eslint-plugin: "^4.6.1",
@typescript-eslint/parser: "^4.6.1",
eslint: "^7.12.1",
eslint-config-prettier: "7.1.0",
eslint-plugin-prettier: "^3.1.4",
jest: "^26.6.3",
prettier: "^2.2.1",
rimraf: "^3.0.2",
ts-jest: "^26.4.4",
ts-loader: "^8.0.14",
ts-node: "^9.1.1",
tsconfig-paths: "^3.9.0",
tsconfig-paths-webpack-plugin: "^3.3.0",
typescript: "^4.0.5",
webpack: "^5.15.0",
webpack-cli: "^4.4.0"
},
jest: {
moduleFileExtensions: [
"js",
"json",
"ts"
],
rootDir: "src",
testRegex: ".*.spec.ts$",
transform: {
^.+.(t|j)s$: "ts-jest"
},
collectCoverageFrom: [
"**/*.(t|j)s"
],
coverageDirectory: "../coverage",
testEnvironment: "node"
},
main: "webpack.config.js",
}

webpack-config

const webpack = require('webpack');
const path = require('path');
const nodeExternals = require('webpack-node-externals');
// const config = require('config');
const isProduction = typeof process.env.NODE_ENV !== 'undefined' && process.env.NODE_ENV === 'production';
const mode = isProduction ? 'production' : 'development';

module.exports = {
    entry: [
      'webpack/hot/poll?100',
      './src/main.ts',
    ],
    optimization: {
        minimize: false,
    },
    target: 'node',
    mode,
    externals: [
      nodeExternals({
          allowlist: ['webpack/hot/poll?100'],
      }),
    ],
    module: {
        rules: [
            {
                test: /.tsx?$/,
                loader: 'ts-loader',
                options: {
                  transpileOnly: true
                },
                exclude: /node_modules/,
              }
        ]
    },
    resolve: {
        extensions: ['.tsx', '.ts', '.js'],
    },
    plugins: [
        new webpack.HotModuleReplacementPlugin(),
        // new webpack.WatchIgnorePlugin([/.js$/, /.d.ts$/]),        
        new webpack.DefinePlugin(
            { 
                // CONFIG: JSON.stringify(config) 
            }
        ),
    ],
    output: {
        path: path.join(__dirname, 'dist'),
        filename: 'main.js',
    },
};

question from:https://stackoverflow.com/questions/65949746/webpack-require-module-not-found-on-the-deployment-server

Answer 1

When using nodeExternals webpack skips bundling the node_modules into the final bundle, so you till need to run your production dependency install command on your production server.

This is done due to low level dependencies of some node packages, like pg needing C++ bindings or bcrypt using node-pre-gyp and python. Bundling these dependencies into your code isn't compatible, which is why they need to be left external. There's a lot of discussion that goes more into depth on this here