My employer (Wikimedia, which is a non-profit) has been running all our server infra on pure open source for many years, for very principled reasons. We even publish all of our internal infrastructure config in public git repos as well. We're an open-source-only shop that's doing very non-hobby work. We have thousands of servers, we run our own CDN on multiple continents, we have somewhere around a billion unique users per month, and our average global rate of inbound HTTP requests is around 135K/second.
However, it keeps getting harder to stick to our open source principles every year as more projects shift towards open-core models with this kind of "Anyone who needs feature X is surely a big corporation making billions who doesn't mind running closed source software" type of thinking. It's not just bad for us, it's bad for the whole larger open source and Internet ecosystems if all the important bits for running at scale are locked up and hidden away in closed-source software.
Avoiding recurring payments you can't easily stop makes reasonable financial sense to me. Particularly for a business that doesn't sell anything.
Many people assume that developing it in-house is a one-time cost. However, in my experience, code is not an asset but a liability for which you will have to pay interest in the form of maintenance. More specifically, in this case there will most likely need to be adjustments made to the in-house extension as the oss nginx version it was built on top is being updated over the years.
My point here is that you should probably treat in-house code as a recurring cost, because in practice it usually is.
The question then becomes which recurring cost is higher: The license or the in-house maintenance?
Accepting these "sprinkles on top" licenses is highly foolish. I do hope that the true free and open source licensed software prevails in the server space. As many as possible must continue to hold out and push forward with new better and better scalable fully open source software.
Curious how deep does it go? Do you only use firmware in server which has open source code. Do you require all drivers to be open source?
> It should be possible to run large-scale important things on pure open source.
It is definitely possible. With enough developer time, you could create copy of any software. Every paid or open core software runs on the philosophy that it is cheaper to pay them rather than to build them.
Which brings to the core issue, developer time is not free or cheap. The fact is that software quality and reliability is dependent on the money that the software has means paid software quality in general should be higher. While wikimedia could get enough money through donation, no one donates to open source projects that could be counted in full time developer salary, likely not even wikipedia(correct me if wrong).