The conceptual difference is that Flask etc are task oriented and Nginx is technology oriented. Specifically it's a kind of expanded instantiation of the entire

The conceptual difference is that Flask etc are task oriented and Nginx is technology oriented. Specifically it's a kind of expanded instantiation of the entire HTTP request cycle with hooks that allow some of the sub-events to be customised. This sounds like a good thing, but is actually a problem in practice. Nginx is one of the few pieces of software that has literally enraged me. The configuration process is so obtuse and full of random gotchas where it does what it wants for no obvious reason - with minimal docs - that it's very hard to get it working the way you want to. One obvious example is that index can trigger an internal rewrite. So you set up a location and Nginx will find your path and index correctly - and then it throws it away and decides to use a different location. Which most likely gets you a 404. You can stop this if you know the magic words, and no doubt there is a Very Good Reason for it. But intuitive it isn't.