So, I've followed through the tutorial to get a basic end point working and it tells me I have to use ESP which is a Google thing based around Nginx.
Do I have to use this? What if I were to run my own web server/reverse proxy?
Would it work? I can't find anything anywhere about this.
To take advantage of Endpoints API Management on GKE/GCE/GAE Flexible environment, the short answer is yes. For App Engine Standard, you can't use ESP and instead have to use the Endpoints Frameworks.