So, for the last 6 months or so, I've had issues with my websites throwing 503 errors after publishing them from Visual Studio. Not always the same error, but something along the lines of multiple apps in the same application pool.
Wasn't really sure what that meant, google didn't provide a good result and it was starting to annoy me.
I host a bunch of my clients websites on my shared hosting server. Some of them are flat static sites, html/css/js... the ones that have given me headaches are the razor pages.
By default my web-apps didn't always have a web.config, mostly probably due to my ignorance, but I've come to understand the meaning and how to set it up correctly to avoid the 503 error.