Recently, I came across an engineering blog by Dropbox, talking about their latest iteration of Robinhood (an in-house built load balancing service). It is designed to dynamically adjust node weights for even load distribution by leveraging Proportional Integral Derivative (PID) controllers. I always had a blurry memory of control theory - But I never really had the opportunity to put it into practice. So, I decided to spent my Christmas evening implementing a PID controller (a mini-version of R...