This article described something I've wanted to do for a bit: using PID (and possibly other control algorithms) to control software systems. I've thought about this for a bit and I have some reservations (perhaps unfounded because I'm just not that knowledgeable) actually trying to implement it in live systems:<p>1. PID tuning is somewhat non-trivial. It's interesting to see that the author was able to tune their PID using a simulation. This is something I've thought about doing for a while but I don't know how I can effectively validate that the simulation approximates reality to an reasonable extent. Sure I could build the simulator and validate it against the live system, but the resource spent doing that might be better off just improving the live system. It would be nice to have some theoretical arguments over why the simulation would be correct. Now this shows my lack of knowledge, so perhaps someone else knows how to deal with this more effectively.<p>2. Software systems these days are always changing, especially when these things are running on your servers that you're constantly updating. Tuned PID constants are only valid for a particular system configuration (the "plant"). If the plant changes too much, the controller performance can degrade, or worse: it can become unstable and blow up. This makes any system controlled by the PID difficult to change: you want to avoid changes to the system because that means you have to retune the PID, which may be difficult to perform. This effectively becomes a technical debt, especially if the original author of the PID no longer works on that project (and assuming only a few knows how it works to begin with).<p>There are some other thoughts about non-linearity of software systems. Although these are routinely dealt with in the real world, it makes a topic that's already somewhat complex even more complicated, which further adds to the non-maintainable status of the controller.<p>This all makes me feel like PID may not be the best choice in software systems, but I don't have concrete proof either.<p>Sorry if this felt a little bit rambling. It's something that has been on my mind for a bit but I haven't had a chance to formalize.