How to fix Yum/DNF issue in CentOS 8

 Symptom:

[root@~]# yum update -y
CentOS Stream 8 - AppStream                                                             0.0  B/s |   0  B     00:00
Errors during downloading metadata for repository 'appstream':
  - Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8-stream&arch=x86_64&repo=AppStream&infra=ec2 [Could not resolve host: mirrorlist.centos.org]
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: Curl error (6): Couldn't resolve host name for http://mirrorlist.centos.org/?release=8-stream&arch=x86_64&repo=AppStream&infra=ec2 [Could not resolve host: mirrorlist.centos.org]

Solution:

cd /etc/yum.repos.d/

sudo sed -i 's/mirrorlist/#mirrorlist/g' /etc/yum.repos.d/CentOS-*
sudo sed -i 's|#baseurl=http://mirror.centos.org|baseurl=http://vault.centos.org|g' /etc/yum.repos.d/CentOS-*
sudo yum update -y