chore: progressing with chapter 12

Author: lmammino

12-scalability-and-architectural-patterns/04-http-cluster-zero-downtime/README.md

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+# 04-http-cluster-zero-downtime
+
+This example demonstrates how to benchmark a simple HTTP server that uses the
+cluster module and provides auto restarting of failed workers.
+
+## Dependencies
+
+This example requires you to install some third-party dependencies from npm.
+
+If you have `pnpm` installed, you can do that with:
+
+```bash
+pnpm install
+```
+
+Alternatively, if you prefer to use another package manager, make sure to delete
+the `pnpm-lock.yaml` file before using it.
+
+If you want to use `npm`, you can run:
+
+```bash
+npm install
+```
+
+If you want to use `yarn`, you can run:
+
+```bash
+yarn install
+```
+
+## Run
+
+To run the example server:
+
+```bash
+npm start # or `node app.js`
+```
+
+To run a benchmark (in another terminal):
+
+```bash
+npm run benchmark # or `npx autocannon http://localhost:8080`
+```

12-scalability-and-architectural-patterns/04-http-cluster-zero-downtime/app.js

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+import cluster from 'node:cluster'
+import { once } from 'node:events'
+import { createServer } from 'node:http'
+import { cpus } from 'node:os'
+
+if (cluster.isPrimary) {
+  const availableCpus = cpus()
+  console.log(`Clustering to ${availableCpus.length} processes`)
+  for (const _ of availableCpus) {
+    cluster.fork()
+  }
+  cluster.on('exit', (worker, code) => {
+    if (code !== 0 && !worker.exitedAfterDisconnect) {
+      console.log(`Worker ${worker.process.pid} crashed. Starting a new worker`)
+      cluster.fork()
+    }
+  })
+  process.on('SIGUSR2', async () => {
+    const workers = Object.values(cluster.workers)
+    for (const worker of workers) {
+      console.log(`Stopping worker: ${worker.process.pid}`)
+      worker.disconnect()
+      await once(worker, 'exit')
+      if (!worker.exitedAfterDisconnect) {
+        continue
+      }
+      const newWorker = cluster.fork()
+      await once(newWorker, 'listening')
+    }
+  })
+} else {
+  const server = createServer((_req, res) => {
+    // simulates CPU intensive work
+    let i = 1e7
+    while (i > 0) {
+      i--
+    }
+
+    console.log(`Handling request from ${process.pid}`)
+    res.end(`Hello from ${process.pid}\n`)
+  })
+
+  server.listen(8080, () => console.log(`Started at ${process.pid}`))
+}

12-scalability-and-architectural-patterns/04-http-cluster-zero-downtime/package.json

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+{
+  "name": "04-http-cluster-zero-downtime",
+  "version": "1.0.0",
+  "description": "This example demonstrates how to benchmark a simple HTTP server that uses the cluster module and provides auto restarting of failed workers",
+  "type": "module",
+  "scripts": {
+    "start": "node app.js",
+    "benchmark": "autocannon http://localhost:8080"
+  },
+  "engines": {
+    "node": ">=24"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "devDependencies": {
+    "autocannon": "^8.0.0"
+  }
+}