Are you getting this error in CentOS 8 when trying to use yum to install a package?
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
What we need to do is not use the automatic mirror list and manually set the base URL
sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS*
sed -i 's%#baseurl=http://mirror.centos.org%baseurl=http://vault.centos.org%g' /etc/yum.repos.d/CentOS*
We had to be creative above with the second sed as it was just easier to use a weird % as the delimiter for the sed statement, as the standard / would not work since the search and replace has a url with /'s in it.
After that run yum again and everything should work