I think this illustrates something important, which is that: You don't need locking. You need <some high-level business constraint that might or might not require some form of locking>.

In your case, the constraint is "don't sell more than N tickets". For most realistic traffic volumes for that kind of problem, you can solve it with traditional rdbms transactional behavior and let it manage whatever locking it uses internally.

I wish developers were a lot slower to reach for "I'll build distributed locks". There's almost always a better answer, but it's specific to each application.