Serverless Webpack Plugin - Significantly reduces Lambda file size and improves performance

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0.4.58 years ago8 years agoMinified + gzip package size for serverless-webpack-plugin in KB


Serverless Webpack Plugin
Forked from serverless-optimizer-plugin this plugin uses webpack to optimize your Serverless Node.js Functions on deployment.
Reducing the file size of your AWS Lambda Functions allows AWS to provision them more quickly, speeding up the response time of your Lambdas. Smaller Lambda sizes also helps you develop faster because you can upload them faster.
This Severless Plugin is absolutely recommended for every project including Lambdas with Node.js.
Note: Requires Serverless v0.5.0.


  • Install the plugin and webpack in the root of your Serverless Project:
npm install serverless-webpack-plugin webpack --save-dev

  • Add the plugin to the plugins array in your Serverless Project's s-project.json, like this:

plugins: [

  • In the custom property of either your s-project.json or s-function.json add an webpack property. The configPath is relative to the project root.

    "custom": {
        "webpack": {
            "configPath": "path/relative/to/project-path"

Webpack config

This plugin allows you to completely customize how your code is optimized by specifying your own webpack config. Heres a sample webpack.config.js:
var webpack = require('webpack');

module.exports = {
  // entry: provided by serverless
  // output: provided by serverless
  target: 'node',
  externals: [
  resolve: {
    extensions: ['', '.js', '.jsx']
  devtool: 'source-map',
  plugins: [
    new webpack.IgnorePlugin(/^\.\/locale$/, /moment$/),
    new webpack.optimize.DedupePlugin(),
    new webpack.optimize.OccurenceOrderPlugin(),
    new webpack.optimize.UglifyJsPlugin({
      compress: {
        unused: true,
        dead_code: true,
        warnings: false,
        drop_debugger: true
  module: {
    loaders: [
        test: /\.jsx?$/,
        loader: 'babel',
        exclude: /node_modules/,
        query: {
          presets: ['es2015', 'stage-0']
Note: Some node modules don't play nicely with webpack.optimize.UglifyJsPlugin in this case, you can omit it from your config, or add the offending modules to externals. For more on externals see below.


Externals specified in your webpack config will be properly packaged into the deployment. This is useful when working with modules that have binary dependencies, are incompatible with webpack.optimize.UglifyJsPlugin or if you simply want to improve build performance. Check out webpack-node-externals for an easy way to externalize all node modules.

Source Maps

Yes using devtool: 'source-map' works, include require('source-map-support').install(); you'll have pretty stacktraces.

Loading additional modules before the lambda function module

If you need to load modules before your lambda function module is loaded, you can specify those modules with entry option in your webpack config. For example if you need to load the babel-polyfill, you can do that by adding entry: ['babel-polyfill'] to your webpack config. This will first load the babel-polyfill module and then your lambda function module.

Improving deploy performance

The plugin builds directly from the source files, using "magic handlers" to include the parent directory (as mentioned in the 0.5.0 release notes) is unnecessary.