When you sign up to a VPS plan you will receive access to your hardware, but it will stay in the provider’s data center. You will obviously need to connect to the machine to be able to work on your server, and that is where virtualization and hypervisors come in. With the help of these you can run programs on your server and manage the content of your website. Let’s check out what these are and what they do.
The word virtualization refers to the process of creating something virtual based on an actual version of something. Hardware virtualization refers to the creation of a virtual machine that acts like a functioning computer. The programs running on the virtual machines are separated from the hardware and the other parts of the computer that the virtual machine is running on.
This allows the virtual private servers to be separated from the resources of the host computer. The host machine is the actual hardware what the virtualization is running on and the virtual machines are called guest machines. The software that creates a virtual machine is called a hypervisor or virtual machine manager, but more about that a bit later.
Virtualization makes it possible to run a complete OS on the guest system. This way you can have Windows running in the host machines and Windows, Linux or any other on the guest machines.
These virtualized operating systems are that you can connect to. The two most important features that is possible thanks to the virtualization are snapshots and migration. Snapshots are a frozen states of the virtual machine, generally the storages of the device.
Making a snapshot is taking the state and saving it, so you can resume operation from that point. This is extremely useful as a backup technique before trying out new updates, new features or simply to restore the normal operation after an attack.
Migration is the process of moving snapshots between virtual machines. This way you can change providers or servers in the same provider without the need to reconfigure everything again or uploading your content one more time.
A hypervisor or virtual machine monitor is a software, firmware or hardware that creates and runs virtual machines. The hypervisor is responsible of connecting the guest operating systems with the hardware that they are using.
This way multiple virtualized operating systems can share the host hardware regarding the type of the guest operating systems. This is where hypervisors differs from operating system level virtualization, where all guests must share a single kernel.
Gerald J. Popek and Robert P. Goldberg classified two types of hypervisor in their 1974 article.
The Type-1 native or bare-metal hypervisors run directly on the host hardware and manages the guest operating systems. The Type 2 or hosted hypervisors run on an operating system on the host hardware. The distinction between the two types are not necessarily clear. The Kernel-based Virtual Machine (KVM) from Linux is converting the host operating system to a type-1 hypervisor for example.
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Kernel-based Virtual Machine (KVM) is a full virtualization solution for Linux on x86 hardware. It consists of a loadable kernel module, kvm.ko, that provides the core virtualization infrastructure and a processor specific module, kvm-intel.ko or kvm-amd.ko. If you choose KVM you can use multiple unmodified Linux or Windows images on your guest machines, with perfectly separated resources. The Kernel-based Virtual Machine is an open-source software, making it up-to-date and widely used.
Linux-VServer provides virtualization for GNU/Linux systems. VServer is working with kernel level isolation, allowing multiple virtual machines to run at once. The guest machines are using separated resources but efficiently, since they are running on the same kernel.
VServer was created by adding operation system-level virtualization to the Linux kernel.The project was started by Jacques Gélinas and now it is developed and distributed as an open-source software. Linux-VServer is a jail mechanism in that it can be used to securely partition resources in such a way that processes cannot mount a denial-of-service attack on anything outside their partition.
OpenVZ is also an operating-system level virtualization like VServer, allowing it to run only Linux guest machines. OpenVZ creates multiple secure, isolated Linux containers (otherwise known as VEs or VPSs) on a single physical server enabling better server utilization and ensuring that applications do not conflict.
Each container performs and executes exactly like a stand-alone server; a container can be rebooted independently and have root access, users, IP addresses, memory, processes, files, applications, system libraries and configuration files. OpenVZ is also an open-source software with all its perks.