Tight coupling

Tight coupling is a structural property of systems in which components are so directly and immediately dependent on one another that a change or failure in one propagates rapidly to others, leaving little time for buffering, adaptation, or local recovery. In tightly coupled systems, the links between nodes have high bandwidth and low delay: information and perturbation travel fast, and the system as a whole behaves more like a single organism than a federation of independent parts.

Tight coupling is the opposite of loose coupling, in which interfaces are buffered, delays are longer, and components can fail independently without cascading. Both have tradeoffs: tight coupling enables efficiency, speed, and coordinated response; loose coupling enables resilience, modularity, and graceful degradation. The efficiency-resilience tradeoff is, in part, a choice between tight and loose coupling. Most catastrophic system failures — from the 2008 financial crisis to the 2010 Flash Crash — involve tight coupling that managers believed was loose.