Script for setting up layer for a lambda containing node.js dependencies

__nodejs_lambda_layer

...

package.json

{
  "name": "my-lambda",
  "private": true,
  "version": "1.0.0",
  "scripts": {
    "prepare": "node prepare_layer.js",
    "package": "yarn prepare && yarn sls package --stage production"
  },
  "dependencies": {
    "//": "...",
    "@google-cloud/language": "^4.2.1"
  }
}

prepare_layer.js

const { mkdirSync, writeFileSync, unlinkSync, renameSync } = require('fs');
const { execSync } = require('child_process');
const { join } = require('path');
const { externals = [] } = require('./webpack.config');
const { dependencies = {} } = require('./package.json');

const layerDir = join(__dirname, '.google-cloud-deps');
const outputDir = join(layerDir, 'nodejs');

// Prepare Output Directories

console.log('Preparing output directories');

execSync(`rm -rf ${layerDir}`);
mkdirSync(outputDir, { recursive: true });

// Write package.json for layer dependencies

console.log('Writing package.json with external dependencies');

const dependenciesToPackage = Object.fromEntries(
  Object.entries(dependencies).filter(([name]) => externals.includes(name))
);

const outputPackageJson = join(layerDir, 'package.json');
const outputPackageJsonContent = JSON.stringify({ dependencies: dependenciesToPackage }, null, 2);
console.log(outputPackageJsonContent);
writeFileSync(outputPackageJson, outputPackageJsonContent);

// Install dependencies and organize layer files

console.log('Installing dependencies and organizing layer structure');

console.log(execSync('yarn --no-lockfile', { cwd: layerDir }).toString());
renameSync(join(layerDir, 'node_modules'), join(outputDir, 'node_modules'));

// Cleanup files

console.log('Cleaning up output folder');
unlinkSync(outputPackageJson);

// Voila!

console.log('Layer files ready!');

serverless.yaml

# ...

layers:
  GoogleCloudDeps:
    path: .google-cloud-deps
    compatibleRuntimes:
      - nodejs12.x

functions:
  my-lambda:
    # ...
    layers:
      - Ref: GoogleCloudDepsLambdaLayer

# ...

webpack.config.js

const baseWebpack = require('../../webpack.config');

module.exports = {
  ...baseWebpack,
  externals: [...baseWebpack.externals, '@google-cloud/language'],
};