fix: bundle generated warmer handler to avoid missing @smithy runtime dependency

package.json

@@ -34,5 +34,8 @@
 		"@biomejs/biome": "2.3.11",
 		"husky": "^9.1.7",
 		"jest": "^30.2.0"
+	},
+	"dependencies": {
+		"esbuild": "^0.27.2"
 	}
 }

src/warmer.js

@@ -3,6 +3,7 @@ const path = require('path');
 const { exec } = require('child_process');
 const util = require('util');
 const { capitalize } = require('./utils');
+const esbuild = require('esbuild');
 
 const execAsync = util.promisify(exec);
 
@@ -124,7 +125,7 @@ const uninstrumentedLambdaClient = new LambdaClient({
 ${
 	tracing
 		? `import * as AWSXRay from 'aws-xray-sdk';
-const lambdaClient = AWSXRay.captureAWSv3Client(uninstrumentedLambdaClient);`
+	const lambdaClient = AWSXRay.captureAWSv3Client(uninstrumentedLambdaClient);`
 		: 'const lambdaClient = uninstrumentedLambdaClient;'
 }
 
@@ -196,6 +197,32 @@ export const warmUp = async (event, context) => {
 		await execAsync('npm init -y', { cwd: handlerFolder });
 		await execAsync('npm install --save aws-xray-sdk-core', { cwd: handlerFolder });
 	}
+
+	// Bundle warmup handler so it does not rely on node_modules at runtime
+	const entryFile = path.join(handlerFolder, 'index.mjs');
+	const bundledFile = path.join(handlerFolder, 'index.bundled.mjs');
+
+	try {
+		await esbuild.build({
+			entryPoints: [entryFile],
+			outfile: bundledFile,
+			bundle: true,
+			platform: 'node',
+			format: 'esm',
+			target: 'node18',
+			packages: 'bundle',
+			// Important: bundle everything needed by the warmer into a single file
+			// (no externals), so the artifact can stay minimal.
+			sourcemap: false,
+			minify: false,
+		});
+
+		// Replace original with bundled output
+		await fs.unlink(entryFile);
+		await fs.rename(bundledFile, entryFile);
+	} catch (error) {
+		throw new Error(`Error bundling warmup function: ${error.message}`);
+	}
 }
 
 /**

test/bakcwardsCompatibility.test.js

@@ -4,10 +4,14 @@ jest.mock('fs', () => ({
 	promises: {
 		mkdir: jest.fn(),
 		unlink: jest.fn(),
+		rename: jest.fn(),
 		writeFile: jest.fn(),
 		rm: jest.fn(),
 	},
 }));
+jest.mock('esbuild', () => ({
+	build: jest.fn(() => Promise.resolve()),
+}));
 
 const fs = require('fs').promises;
 const path = require('path');
@@ -71,6 +75,13 @@ describe('Backward compatibility', () => {
 			fs.mkdir.mockResolvedValue(undefined);
 			fs.writeFile.mockClear();
 			fs.writeFile.mockResolvedValue(undefined);
+			fs.unlink.mockClear();
+			fs.unlink.mockResolvedValue(undefined);
+			fs.rename.mockClear();
+			fs.rename.mockResolvedValue(undefined);
+			const esbuild = require('esbuild');
+			esbuild.build.mockClear();
+			esbuild.build.mockResolvedValue({});
 		});
 
 		it('should fallback to servicePath if serviceDir is not defined', async () => {

test/hook.warmupAddWamersAddWamers.test.js

@@ -4,15 +4,20 @@ jest.mock('fs', () => ({
 	promises: {
 		mkdir: jest.fn(),
 		unlink: jest.fn(),
+		rename: jest.fn(),
 		writeFile: jest.fn(),
 		rm: jest.fn(),
 	},
 }));
 jest.mock('child_process', () => ({
 	exec: jest.fn((_path, _opts, cb) => cb()),
 }));
+jest.mock('esbuild', () => ({
+	build: jest.fn(() => Promise.resolve()),
+}));
 const fs = require('fs').promises;
 const { exec } = require('child_process');
+const esbuild = require('esbuild');
 const path = require('path');
 const WarmUp = require('../src/index');
 const {
@@ -30,7 +35,13 @@ describe('Serverless warmup plugin warmup:warmers:addWarmers:addWarmers hook', (
 		fs.mkdir.mockResolvedValue(undefined);
 		fs.writeFile.mockClear();
 		fs.writeFile.mockResolvedValue(undefined);
+		fs.unlink.mockClear();
+		fs.unlink.mockResolvedValue(undefined);
+		fs.rename.mockClear();
+		fs.rename.mockResolvedValue(undefined);
 		exec.mockClear();
+		esbuild.build.mockClear();
+		esbuild.build.mockResolvedValue({});
 	});
 
 	it('Should be called after package:initialize', async () => {
@@ -2756,6 +2767,52 @@ describe('Serverless warmup plugin warmup:warmers:addWarmers:addWarmers hook', (
 				}),
 			);
 		});
+
+		it('Should bundle warmup handler with esbuild to make it self-contained', async () => {
+			const serverless = getServerlessConfig({
+				service: {
+					custom: {
+						warmup: {
+							default: {
+								enabled: true,
+							},
+						},
+					},
+					functions: { someFunc1: { name: 'someFunc1' }, someFunc2: { name: 'someFunc2' } },
+				},
+			});
+			const pluginUtils = getPluginUtils();
+			const plugin = new WarmUp(serverless, {}, pluginUtils);
+
+			await plugin.hooks['before:warmup:addWarmers:addWarmers']();
+			await plugin.hooks['warmup:addWarmers:addWarmers']();
+
+			const handlerFolder = path.join('testPath', '.warmup', 'default');
+			const entryFile = path.join(handlerFolder, 'index.mjs');
+			const bundledFile = path.join(handlerFolder, 'index.bundled.mjs');
+
+			// Verify esbuild.build was called with correct parameters
+			expect(esbuild.build).toHaveBeenCalledTimes(1);
+			expect(esbuild.build).toHaveBeenCalledWith({
+				entryPoints: [entryFile],
+				outfile: bundledFile,
+				bundle: true,
+				platform: 'node',
+				packages: 'bundle',
+				format: 'esm',
+				target: 'node18',
+				sourcemap: false,
+				minify: false,
+			});
+
+			// Verify the original file was deleted
+			expect(fs.unlink).toHaveBeenCalledTimes(1);
+			expect(fs.unlink).toHaveBeenCalledWith(entryFile);
+
+			// Verify the bundled file was renamed to replace the original
+			expect(fs.rename).toHaveBeenCalledTimes(1);
+			expect(fs.rename).toHaveBeenCalledWith(bundledFile, entryFile);
+		});
 	});
 
 	describe('Other plugins integrations', () => {