Feedback control for computer systems applies classical control theory—originally used for physical systems like engines—to digital environments like web servers, databases, and caches. It enables systems to self-adjust to maintain performance goals despite unpredictable workloads or resource shifts. ⚙️ Core Concepts of Feedback Control

The primary objective of a feedback loop is to minimize the —the difference between a desired state ( Setpoint ) and the actual state ( Measured Output ). Setpoint (

The controller is the most common algorithm used to close the feedback loop. Feedback Control for Computer Systems [Book] - O'Reilly

): The target value (e.g., a 95% cache hit rate or 200ms latency). Controller (

): The lever the controller pulls (e.g., scaling server instances or adjusting cache size). The computer process being managed. Measured Output ( ): The actual current performance metric. 🛠️ The PID Controller: The Standard Algorithm

): The algorithm that calculates what change to apply based on the error. Control Input (