Just for completeness:
GitHub or docker might do the trick.
It's basically a micro service implemented in java/spring boot, which is wrapping pdflatex. Urls are immutable and the pdfs are stored on disk/distributed storage. You'll have to host it on your own though. The code is pretty simple and you're able/allowed to customize it to your needs. See the "Scaling the service" section in readme for more details about setting up a production environment.
