Published: March 18, 2026 3 AM, October 2025. A single DNS configuration error on an AWS server brought Snapchat, Roblox, and McDonald's to a standstill. 3,500 companies across 60 countries were stopped cold by one small crack. Systems are far more fragile than we think. Large-scale processing isn't a trend about boosting server specs. It's the engineering discipline that keeps services alive at the edge of their limits. So where does "large-scale" actually begin? 10,000 users? A million? That's the wrong question. Large-scale isn't a number. It's the moment a system hits the ceiling of its available resources. That's why what's a normal Tuesday for Amazon can be a catastrophe for a growing startup. This series is about how to detect that ceiling, understand why systems break, and build things that hold. The Signals Before a System Breaks Systems don't collapse without warning. There are always signs. The Google SRE team calls them the Four Golden Signals . ref.…