Updating Plesk or system packages on CentOS 8 server fails: Failed to download metadata for repo: Cannot prepare internal mirrorlist: No URLs in mirrorlist

Symptoms

• After January 31st, 2022, updating Plesk or system packages either via Tools & Settings > System Updates or manually with dnf update on a server with CentOS 8 fails:

  PLESK_ERROR: Failed to check system configuration - Yum utility finished with errors. Installation may fail.
  dnf.exceptions.RepoError: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
  
  Plesk pre-upgrade check
  Error: Cache-only enabled but no cache for 'appstream'
  WARNING: Unable to detect package duplicates: /usr/bin/package-cleanup --dupes returns 1.Output is:

  Note: repository name in the error may be different, for example, baseos or powertools.

• In the Tools & Settings > Updates menu buttons may be greyed out and the following error may be present:

  PLESK_WARN: There are no products for your operating system
  ( 'CentOS' 'Linux' '8.2.2004' 'x86_64' ) available
  from the selected source.

Cause

CentOS 8 reached its end-of-life on December 31st, 2021, and thus, since January 31st, 2022, repositories for that OS were disabled by its vendor and archived to https://vault.centos.org/.

Resolution

Use one of the solutions:

• Convert the server in-place to AlmaLinux 8 (recommended), Rocky Linux 8, or CloudLinux 8 (note that CloudLinux is a paid OS).

• Deploy a new Plesk server with a supported operating system and migrate to it using Plesk Migrator.

• Temporary solution: configure archived repositories (not recommended)

  1. Connect to the server using SSH.

  2. Edit the files /etc/yum.repos.d/CentOS-Linux-AppStream.repo, /etc/yum.repos.d/CentOS-Linux-BaseOS.repo, and /etc/yum.repos.d/CentOS-Linux-PowerTools.repo so they look like below:

     • /etc/yum.repos.d/CentOS-Linux-AppStream.repo:

       [appstream]
       name=CentOS Linux $releasever - AppStream
       baseurl=http://vault.centos.org/$contentdir/$releasever/AppStream/$basearch/os/
       gpgcheck=1
       enabled=1
       gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial

     • /etc/yum.repos.d/CentOS-Linux-BaseOS.repo:

       [baseos]
       name=CentOS Linux $releasever - BaseOS
       baseurl=http://vault.centos.org/$contentdir/$releasever/BaseOS/$basearch/os/
       gpgcheck=1
       enabled=1
       gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial

     • /etc/yum.repos.d/CentOS-Linux-PowerTools.repo:

       [powertools]
       name=CentOS Linux $releasever - PowerTools
       baseurl=http://vault.centos.org/$contentdir/$releasever/PowerTools/$basearch/os/
       gpgcheck=1
       enabled=1
       gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-centosofficial