Add example of custom sandbox domain proxy

Author: ValentaTomas

examples/custom-sandbox-domain-proxy/.env.template

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+# TODO: Get your E2B API key from https://e2b.dev/docs/getting-started/api-key
+E2B_API_KEY=""

examples/custom-sandbox-domain-proxy/.gitignore

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+.env
+node_modules

examples/custom-sandbox-domain-proxy/README.md

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+# Custom Sandbox Domain Proxy
+
+Example of mapping custom subdomains to your E2B sandboxes. Access sandboxes at `my-app.yourdomain.com` instead of default URLs.
+
+## Tech Stack
+- [E2B Code Interpreter SDK](https://github.com/e2b-dev/code-interpreter)
+- Express.js
+
+## How It Works
+1. Create E2B sandbox, start Python HTTP server inside (port 8000)
+2. Generate custom subdomain (e.g., `happy-blue-tiger`)
+3. Map subdomain → sandbox ID in `sandboxCustomSubdomains` object
+4. Express proxy extracts subdomain from requests, looks up sandbox ID, forwards to E2B sandbox
+5. Works with any domain (`.localhost` for dev, your domain in production)
+
+## Setup
+### 1. Set up API keys
+- Copy `.env.template` to `.env`
+- Get your [E2B API KEY](https://e2b.dev/docs/getting-started/api-key) and add it to `.env`
+
+### 2. Install packagesInstall the E2B Code Interpreter SDK and other dependencies
+
+```bash
+npm i
+```
+
+### 3. Run the example
+```bash
+npm run start
+```
+
+This creates a sandbox, assigns it a custom subdomain, starts the proxy on port 3000, and opens your browser.
+
+Press `Ctrl+C` to stop and cleanup.
+
+## Use Cases
+- Branded URLs instead of random IDs
+- Multi-tenant apps: one subdomain per user (`user-123.yourapp.com`)
+- Named environments: dev/staging/prod
+
+## Learn More
+[E2B Documentation](https://e2b.dev/docs)

examples/custom-sandbox-domain-proxy/app.ts

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+import { Sandbox } from '@e2b/code-interpreter'
+import express from 'express'
+import { createProxyMiddleware } from 'http-proxy-middleware'
+import open from 'open'
+import { uniqueNamesGenerator, adjectives, colors, animals } from 'unique-names-generator'
+import 'dotenv/config'
+
+// Start sandbox
+const sandbox = await Sandbox.create({
+    apiKey: process.env.E2B_API_KEY,
+})
+console.log(`Sandbox created: ${sandbox.sandboxId}`)
+
+
+// Start python file serving server inside of the sandbox
+const PORT_IN_SANDBOX = 8000
+await sandbox.commands.run(
+    `python3 -m http.server ${PORT_IN_SANDBOX}`,
+    { background: true, cwd: '/', user: 'root' }
+)
+console.log(`Python HTTP server started on port ${PORT_IN_SANDBOX} inside sandbox`)
+
+
+// Start express proxy to proxy requests to the sandbox
+// Map custom subdomains to sandbox IDs - users can customize these subdomains however they want.
+const customSubdomain = uniqueNamesGenerator({
+    dictionaries: [adjectives, colors, animals],
+    separator: '-',
+    length: 3,
+})
+const sandboxCustomSubdomains: Record<string, string> = {
+    [customSubdomain]: sandbox.sandboxId,
+}
+
+const app = express()
+const PROXY_PORT = process.env.PORT ? parseInt(process.env.PORT) : 80
+
+// Proxy middleware that maps custom subdomains to sandbox IDs
+app.use((req, res, next) => {
+    const host = req.headers.host || ''
+    const subdomain = host.split('.')[0]
+
+    // Check if this is a subdomain request (has at least one dot)
+    if (!host.includes('.')) {
+        return res.status(400).send('Please use subdomain format: <custom-subdomain>.<domain>')
+    }
+
+    // Look up sandbox ID by custom subdomain
+    const sandboxId = sandboxCustomSubdomains[subdomain]
+
+    if (!sandboxId) {
+        return res.status(404).send(`Sandbox with subdomain "${subdomain}" not found`)
+    }
+
+    // Get the sandbox hostname for proxying
+    const sandboxHost = sandbox.getHost(PORT_IN_SANDBOX)
+
+    // Create proxy middleware dynamically
+    const proxy = createProxyMiddleware({
+        target: `https://${sandboxHost}`,
+        changeOrigin: true,
+        secure: true,
+    })
+
+    return proxy(req, res, next)
+})
+
+app.listen(PROXY_PORT, () => {
+    console.log(`Proxy server running on http://localhost:${PROXY_PORT}`)
+    console.log(`Sandbox ${sandbox.sandboxId} accessible via custom subdomain: "${customSubdomain}"`)
+    console.log(`Access via: http://${customSubdomain}.localhost:${PROXY_PORT}/`)
+})
+
+// Open browser pointing to the custom subdomain
+await open(`http://${customSubdomain}.localhost:${PROXY_PORT}/`)
+
+// Keep process alive and handle cleanup
+process.on('SIGINT', async () => {
+    console.log('\nShutting down...')
+    await sandbox.kill()
+    process.exit(0)
+})