https://ibmimedia.com/blog/66/solve-apache-error-ah01276-cannot-serve-directory
Looks like you are exposing port 5001 from local machine to port 80 on the docker instance, but then you are defining your #virtual #host on port 5001. So your site-default.conf it probably should read:
<VirtualHost *:80>
Notice that the error is about /var/www/html/ (some #Apache default directory) and not your own /usr/src/fileserver/public
