In the past, a physical server usually ran exactly one application, and the server was barely utilized most of the time. Virtualization separates the software from the hardware: several virtual servers share the resources of one or more physical hosts. This saves hardware, power, and space and makes IT more flexible. Today, virtualization is the foundation of most data centers and cloud platforms.
How does virtualization work?
At its core is the hypervisor, a software layer that distributes processor, memory, storage, and network among several virtual machines (VMs) and isolates them from each other.
- Type 1 hypervisors run directly on the hardware and are used in data centers. Well-known examples are Microsoft Hyper-V, VMware ESXi, and KVM, on which Proxmox, for example, is based.
- Type 2 hypervisors run as a program on an ordinary operating system and are suited mainly for testing and development.
A VM essentially consists of files for virtual disks and configuration. It can be copied, moved, and reset to an earlier state via snapshot. Several hosts with shared storage form a cluster: if one host fails, its VMs restart on another. During operation, they can be moved between hosts without interruption.
Besides servers, desktops, networks, and storage are also virtualized. Containers are a lighter variant in which applications share the operating system kernel.
Typical examples
- Domain controllers, file servers, and line-of-business applications run together on a few hosts.
- Before an update of the inventory management system, a snapshot is created so that you can return quickly if problems arise.
- A copy of a server is provided at short notice for a test.
- Workstations are provided centrally, for example with Azure Virtual Desktop.
What companies should keep in mind
- Protect the hypervisor: Place management access in a separate network segment, secure it with multi-factor authentication, and install updates promptly. Attackers specifically target hypervisors because this lets them hit many systems at once.
- Snapshots are not backups: Back up VMs regularly and separately from the host, for example according to the 3-2-1 backup rule.
- Plan reserves: The remaining hosts must be able to absorb the failure of one host.
- Keep an eye on licenses: Licensing models for hypervisors and for software in VMs can change and should be reviewed regularly.
How it differs
Virtualization is a technology; cloud is a delivery model. Cloud platforms use virtualization and add self-service, usage-based billing, and automation, see IaaS, PaaS, and SaaS.
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