Over the years, this issue has happened to me a few times and I always seem to forget the cause and spend 10-20 minutes remembering. This usually happens when I start working with a new client on a brand new laptop. After getting the solution to build, when I try to view the site in IIS I get a 503 error like so:
Looking in the windows application log, IIS log and Episerver logs never shows anything useful. After some head scratching, I usually have a look a the IIS roles installed on the server and that’s when I usually notice Url Rewrite is not installing.
That’s when I head over to the MS site, download it and install it. After doing an IIS reset the 503 usually goes away and I can see a stack trace. If you are in the same boat and nothing useful is being logged, then it’s a sign that the application hasn’t run yet and the issue is higher up in the pipeline. If you are getting a 503, make sure that any module your site depends on is installed and that all your IIS features look correct.