chore: continuing with chapter 12

Author: lmammino

12-scalability-and-architectural-patterns/07-peer-to-peer-load-balancing/README.md

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+# 07-peer-to-peer-load-balancing
+
+This example demonstrates how to implement peer-to-peer load balancing
+
+## Run
+
+Run 2 instances of the app with:
+
+```bash
+node app.js 8081
+node app.js 8082
+```
+
+Now run the client with:
+
+```bash
+node client.js
+```
+
+We should notice how each request is sent to a different server, confirming that
+we are now able to balance the load without a dedicated reverse proxy!

12-scalability-and-architectural-patterns/07-peer-to-peer-load-balancing/app.js

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+import { createServer } from 'node:http'
+
+const { pid } = process
+const server = createServer((req, res) => {
+  const url = new URL(req.url, `http://${req.headers.host}`)
+  const searchParams = url.searchParams
+
+  console.log(`Handling request ${searchParams.get('request')} from ${pid}`)
+  res.end(`Hello from ${pid}\n`)
+})
+
+const port = Number.parseInt(process.env.PORT || process.argv[2]) || 8080
+server.listen(port, () => console.log(`Started at ${pid}`))

12-scalability-and-architectural-patterns/07-peer-to-peer-load-balancing/balancedRequest.js

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+const servers = [
+  { host: 'localhost', port: 8081 },
+  { host: 'localhost', port: 8082 },
+]
+let i = 0
+
+export function balancedRequest(url, fetchOptions = {}) {
+  i = (i + 1) % servers.length
+  const server = servers[i]
+
+  const rewrittenUrl = new URL(url, `http://${server.host}:${server.port}`)
+  rewrittenUrl.host = `${server.host}:${server.port}`
+
+  return fetch(rewrittenUrl.toString(), fetchOptions)
+}

12-scalability-and-architectural-patterns/07-peer-to-peer-load-balancing/client.js

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+import { balancedRequest } from './balancedRequest.js'
+
+for (let i = 0; i < 10; i++) {
+  const response = await balancedRequest(`/?request=${i}`)
+  const body = await response.text()
+  console.log(
+    `Request ${i} completed\nStatus: ${response.status}\nBody: ${body}`
+  )
+}

12-scalability-and-architectural-patterns/07-peer-to-peer-load-balancing/package.json

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+{
+  "name": "07-peer-to-peer-load-balancing",
+  "version": "1.0.0",
+  "description": "This example demonstrates how to implement peer-to-peer load balancing",
+  "type": "module",
+  "scripts": {},
+  "engines": {
+    "node": ">=24"
+  },
+  "engineStrict": true,
+  "keywords": [],
+  "author": "Luciano Mammino and Mario Casciaro",
+  "license": "MIT",
+  "devDependencies": {},
+  "dependencies": {}
+}