SymptomsWhen I try to upgrade my Parallels Plesk Panel (PP) from its web interface, it either keeps loading and nothing happens, or it is being very slow.
CauseMost probably PP is facing issues with name resolving - connection to DNS server is slow or has been lost.
Note: If you are upgrading from a version 9.x or lower to a version 10.x or higher, the upgrade may take a considerable amount of time. This is due to major changes in business logic, user model and overall product functionality. On highly loaded environments the wait times may be more than a day.
ResolutionTry configuring another name server that your PP server uses for resolving host names.
In Linux it can be done by adding a record to /etc/resolv.conf , for example add the following record without quotes and retry the upgrade: