Hypervisors play an essential role in enabling server virtualization, which is itself essential to enabling cloud computing. Broadly speaking, virtualization refers to the use of software to simulate or emulate physical resources. In the case of server virtualization, a hypervisor is a software process that creates and runs virtual machines (VMs) using the resources of physical hardware. The hypervisor abstracts and isolates the VMs and their programs from the underlying server hardware, enabling a more efficient use of physical resources, simpler maintenance and operations, and reduced costs.
Why use a hypervisor?
The primary technological problem that hypervisors solved was that most physical hardware could run only one operating system at a time. This constraint often led to wasted resources, as a single OS seldom fully utilized the hardware’s capacity.
Hypervisors address the above constraint by aggregating the resources of virtualized physical servers (such as memory, network bandwidth and CPU cycles) and then allocating those resources to virtual environments, called virtual machines. Hypervisors are also known as virtual machine monitors (VMM). A VM is essentially a software-based computer, with access to the same resources as a physical computer, including an OS and apps. However, a hypervisor lets you run multiple VMs as guests, thereby using the physical resources of the underlying host machine much more efficiently. Each VM can act as a dedicated machine for every service, app or operating system, allowing you, for example, to run multiple different OSs on a single server. The hypervisor also separates the VMs logically, which protects each individual VM against the effects of problems with other individual VMs on the same hypervisor, such as crashing, errors, or security attacks.
What are the benefits of hypervisors?
As software, hypervisors decouple the OS and apps from the physical host. This decoupling provides an array of benefits, including the ability to easily and quickly migrate the VM from one host to another without disruption. This capacity, called live migration, is essential for workload balancing. Live migration also occurs automatically in the case of node failure, providing high availability and increased uptime.
Virtualization enables cost savings through reducing physical footprint, which in turn reduces costs for electricity, cooling, and maintenance. Virtualization also greatly improves agility and speed in delivering IT services. For example, it is far easier to spin up a VM than to provision new environments to satisfy customer requests.