Virtualization
EFFECTIVE AND FLEXIBLE USE OF IT INFRASTRUCTURE
Currently available servers are designed to take advantage of virtualization. Thanks to this technique, on a single physical server we can run practically any (limited by server resources) number of virtual machines, which are independent operating systems with their own CPU and RAM resources, access to mass storage, and network interfaces.
Virtualization, in addition to the above mentioned way of effective use of existing hardware, allows for a number of additional functions that are impossible or very difficult to achieve using traditional physical servers.
The most important include HA (High Availability) and "live" migration. (Live).
HA is simply a reliability cluster consisting of at least two servers, providing resistance to physical server failure. In case of a server failure, the virtual machines running on it will be automatically activated on the other servers in the cluster according to certain rules (e.g. order).
Another very useful feature of virtualization is the migration of machines between physical servers while they are running. This is very useful in situations where one of the servers needs to be shut down, e.g. for maintenance purposes or because of e.g. memory expansion. Then, without any noticeable interruption to the users, it is possible to release the load on a particular server and turn it off. This mechanism is also often used for load balancing on servers in a cluster.
