> Next, we keep the DERP network costs under control… by trying to never use it. When using Tailscale, almost all of your traffic goes peer to peer, so DERP is only used as a backup. We continue to improve our core product so it can build point-to-point links in ever-more-obscure situations.

This is mentioned in passing, but shows a very good technique. They incentivize technical excellence by tying it to a concrete cost. A free plan, with DERP, is the sacred cow that must not ever be removed. If they don't fix the "ever more obscure situations", then the cost goes up. If they pay an engineer to investigate and fix this, not only does the engineer get to do interesting technical work, and not only does the system become more reliable and "good", they can also think of it as increasing the profit margin of the product (by not increasing costs).

I worked with Avery on Google Fiber, and we did the same thing. Our sacred cow was excellent US-based phone support. That is quite expensive. If there were bugs in our product, users would call in, and our call center costs would increase because we'd have to have more people working. So every week in our team meeting, we would look at summaries of calls, and take on engineering work to address the most common class of problems. That let us scale up the business and still provide friendly and competent phone support, because we were reducing the problems that people called in about. (This was things like having our Wifi access points steer 5GHz capable devices away from flakier 2.4GHz signals, or fixing "black screen" bugs where TV randomly stopped playing for software or network reasons.) Because we had that "sacred cow", every obscure bug that we spent months fixing not only made the product better and were intellectually stimulating to finally figure out, but had a concrete impact on how costly it was to deliver the service.

What most companies would do here to reduce costs is simple. Don't fix DERP bugs, just charge for it. Don't fix "black screen" bugs, just hide the phone number on your website so people can't figure out to call.

Avery has found the perfect balance between cost reduction, interesting engineering, and the somewhat nebulous "good product". Normally conflicting concerns, all living together in harmony. If everyone copied his technique here, the world would be a better place.