After CentOS 8.1 minimal installation, and Cockpit is not installed, then if you want the Web console Cockpit to manage KVM virtual machine, you'll need to install it, how to install? You can install it using the following command:
# yum install Cockpit 
installed cockpit, Web console is not started by default case, you use the following command to enable it:
#systemctl enable --now cockpit.socket 
After installing the Web-based interface as shown below shows:
Cockpit role console
Cockpit is a Web console that has a Web-based interface is easy to use, so that you can perform administrative tasks on the server. It allows you to access it through mobile devices. It can perform a variety of tasks, it's a variety of tasks you can see the following web pages. 
By default, the virtual machine module is not included in the standard Cockpit installation. We need to start the installation package from the cockpit-machines other software package, which can be installed by two ways:
① the command-line installation: # yum install cockpit-machines 
② through the cockpit's Web console installed
open the Web browser, cockpit using a 9090 port, for example:
to access the cockpit Web console example: https: // <host-ip >: 9090 
to see the menu on the left "virtual machine" option after you click install, and then click on the right the "Creat VM", you can create a new "virtual machine" as shown below: 
At this point, you are free to manage your virtual machines and new, is not very practical.