1.4. The Admin's Mental Model: Layers, Dependencies, and Blast Radius

💡 First Principle: Every server is a stack of interdependent layers. A failure at any layer affects every layer above it. Understanding this dependency structure is what separates systematic troubleshooting from random fix attempts—and what makes change management a safety practice, not just a formality.

When something breaks, the first question is always "which layer is the problem in?" An application that can't connect to a database might have a network problem (physical layer), a firewall rule (configuration), a DNS failure (service), or a bug in the application itself. Chasing the wrong layer wastes time and can introduce new problems.