I have a mystery. So I set up an Azure Web app on Linux that pulls from a custom docker image stored in Azure container repo. The dockerfile for the image is pretty simple - ubuntu:latest as the base, installs apache, php, and wordpress using apt-get, sets config files, etc. I can bring up the Wordpress site just fine and do all the expected operations in the administration of it. Except none of the images load (png/jpg/svg/woff/woff2), even if I upload a new image in the wp-admin interface. Every image gives a 502 Bad gateway error.
Looking a bit deeper at the server response, the response headers for images say "Server: Microsoft-IIS/10.0." Wth? How did IIS get on here? If I look at the response for the base WP home page (or any text/html/php file), it says "Server: Apache/2.4.41 (Ubuntu)" as expected.
The bad gateway error makes me think somehow IIS has been set up as a proxy for certain file types, but I haven't set up any proxies in my configs (I may set up nginx in the future, but that's a story for another day). I'm fairly new to Azure web apps, so I wouldn't be surprised if I'm missing something obvious. Any ideas?