The historical context of virtualization

Traditional virtualization appeared on the Linux kernel in the form of hypervisors such as Xen and KVM. This allowed users to isolate their runtime environment in the form of virtual machines (VMs). Virtual machines run their own operating system kernel. Users attempted to use the resources on host machines as much as possible. However, high densities were difficult to achieve with this form of virtualization, especially when a deployed application was small in size compared to a kernel; most of the host's memory was consumed by multiple copies of kernels running on it. Hence, in such high-density workloads, machines were pided using technologies such as chroot jails which provided imperfect workload isolation and carried security implications.

In 2001, an operating system virtualization in the form of Linux vServer was introduced as a series of kernel patches.

This led to an early form of container virtualization. In such forms of virtualization, the kernel groups and isolates processes belonging to different tenants, each sharing the same kernel.

Here is a table that explains the various developments that took place to enable operating system virtualization: