Deploying a new version of your app without kicking users out or causing errors sounds like a dream, right? Let's make it real. The Problem You git push, run your build, restart the server... and for 5–30 seconds, your users see: Cannot GET / 502 Bad Gateway Or just a blank white screen of sadness That's downtime. In 2025, it's not acceptable. The Setup We'll assume: Frontend: React (built with Vite or CRA) Backend: Node.js + Express Server: Linux (Ubuntu) Process manager: PM2 The Strategy The goal: Old version keeps running until new version is ready. Here's the plan: Build the new React bundle Prepare the new Node backend Switch traffic atomically Handle in-flight requests gracefully Step 1: Build in a Staging Directory Don't overwrite your live files directly.…