Even the most interesting technical things Yelp is doing probably involve reinventing something hundreds of other companies have already reinvented, because the

Even the most interesting technical things Yelp is doing probably involve reinventing something hundreds of other companies have already reinvented, because the existing things don’t work with their infrastructure or they’re written in the wrong language or they’re just kinda bad and maybe doing it from scratch will be better. After 20-some-odd years in the industry... oof. Sometimes it feels like groundhog day. You might have thought about web application authorization. You may have implemented it a few times and figured out how it ought to be done. And you might think that after twenty years it would be a solved problem. But you would be wrong. You're going to encounter yet another web application with a bespoke authorization system. It's going to take a shotgun approach to validation and nobody will be able to tell you if it works the way it's supposed to or not. The tests pass (if there are any). It might have errors in it but we haven't had any reports yet. We hired a pentester last year and they didn't find anything. It's probably fine. So you add a new feature and you need to extend this authorization system to handle it and you spend most of your time trying to make sure things continue working instead of focusing on what matters. The same thing over and over again. The same libraries, the same mistakes, the same solutions.