title: Running a Webpack Dev Server inside a webpack bundle
body: <p>I have a webpack configuration for a node server running with Express. The entry file if it's in production runs the Express server, if in development also runs the Express Server and a Webpack Dev Server. The problem lies when the webpack dev server is initialized; it complains about <code>Unhandled rejection Error: invalid argument</code> or not found paths. The client configuration that is used in the webpack dev server runs well when used on it's own from the CLI, also it works when the webpackdevserver is initialized in a regular (not-bundled) file.</p>
  
  <p>The difference from each method is the paths that are printed from the configuration are different between the cases that work and the one that doesn't. These paths are resolved from the __dirname which is different in each case. Why could the reason for this be, and is it possible to obtain the normal __dirname path?</p>
  
  <p>Thanks in advance.</p>
  
  <p>Server Config:</p>
  
  <pre><code>{
    target: 'node',
    entry: rootDirectory,
    externals: nodeModules,//readDirSync('node_modules').filter(x =&gt; x !== '.bin'),
    output: {
      path: join(rootDirectory, 'build'),
      filename: 'index.js'
    },
    module: {
      loaders: [
        {
          test: /\.js$/,
          exclude: /node_modules/,
          loader: 'babel'
        }
      ]
    },
    plugins: [
      new DefinePlugin({
        'process.env': {
          'NODE_ENV': JSON.stringify('development'),
          'PORT': 8080,
          'SERVER': true,
          'CLIENT': false
        }
      })
    ],
    node: {
      __dirname: false,
      __filename: false
    }
  };
  </code></pre>
  
  <p>Client Config:</p>
  
  <pre><code>{
    entry: {
      client: [
        'webpack-dev-server/client?http://localhost:8080',
        'webpack/hot/only-dev-server',
        './client'
      ]
    },
    output: {
      path: join(rootDirectory, 'public'),
      filename: 'bundle.js',
      publicPath: ''
    },
    module: {
      loaders: [
        {
          test: /\.js$/,
          exclude: /node_modules/,
          loader: 'babel'
        }
      ]
    },
    plugins: [
      // new DefinePlugin({
      //   'process.env': {
      //     'NODE_ENV': JSON.stringify('development'),
      //     'PORT': 8080,
      //     'SERVER': false,
      //     'CLIENT': true
      //   }
      // }),
      new HTMLWebpackPlugin({
        template: './index.tmp.html',
        filename: 'index.html',
        chunks: ['client']
      }),
      new webpack.HotModuleReplacementPlugin()
    ]
  }
  </code></pre>
  
  <p>index.js</p>
  
  <pre><code>import devServer from './devServer';
  import server from './server';
  
  const PORT = process.env.PORT || 8080;
  
  switch (process.env.NODE_ENV || 'development') {
    case 'development': devServer(PORT);
    case 'production': server(PORT - 1);
  }
  </code></pre>
  
  <p>devServer.js</p>
  
  <pre><code>// import Express from 'express';
  import webpack from 'webpack';
  import WebpackDevServer from 'webpack-dev-server';
  // import webpackDevMiddleware from 'webpack-dev-middleware';
  // import webpackHotMiddleware from 'webpack-hot-middleware';
  
  import {join} from 'path';
  
  import config from './webpack/dev/client.config';
  
  export default (PORT) =&gt; {
    // let app = new Express();
    let compiler = webpack(config);
    let serverOptions = {
      inline: true,
      hot: true,
      contentBase: '/public',
      publicPath: config.output.publicPath,
      proxy: {
        '*': `http://localhost:${PORT - 1}`
      }
    }
    let app = new WebpackDevServer(compiler, serverOptions);
    app.listen(PORT);
  }
  </code></pre>
  
  <p>client.js</p>
  
  <pre><code>console.log('hello world');
  </code></pre>
  
  <p>code structure</p>
  
  <pre><code>./index.js
  ./server.js
  ./devServer.js
  ./client.js
  ./webpack/dev/server.config.js
  ./webpack/dev/client.js
  ./public
  ./build
  </code></pre>
  
  <p>Error Stack</p>
  
  <pre><code>Unhandled rejection Error: invalid argument
      at pathToArray (/Users/AJ/Desktop/winebox/node_modules/memory-fs/lib/MemoryFileSystem.js:44:10)
      at MemoryFileSystem.mkdirpSync (/Users/AJ/Desktop/winebox/node_modules/memory-fs/lib/MemoryFileSystem.js:139:13)
      at MemoryFileSystem.(anonymous function) [as mkdirp] (/Users/AJ/Desktop/winebox/node_modules/memory-fs/lib/MemoryFileSystem.js:279:34)
      at Compiler.&lt;anonymous&gt; (/Users/AJ/Desktop/winebox/node_modules/webpack/lib/Compiler.js:229:25)
      at Compiler.next (/Users/AJ/Desktop/winebox/node_modules/tapable/lib/Tapable.js:67:11)
      at /Users/AJ/Desktop/winebox/node_modules/html-webpack-plugin/index.js:163:9
      at PassThroughHandlerContext.finallyHandler (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/finally.js:55:23)
      at PassThroughHandlerContext.tryCatcher (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/util.js:16:23)
      at Promise._settlePromiseFromHandler (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/promise.js:503:31)
      at Promise._settlePromise (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/promise.js:560:18)
      at Promise._settlePromise0 (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/promise.js:605:10)
      at Promise._settlePromises (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/promise.js:684:18)
      at Async._drainQueue (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/async.js:126:16)
      at Async._drainQueues (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/async.js:136:10)
      at Immediate.Async.drainQueues [as _onImmediate] (/Users/AJ/Desktop/winebox/node_modules/bluebird/js/release/async.js:16:14)
      at processImmediate [as _immediateCallback] (timers.js:383:17)
  </code></pre>