1.3 Virtualization and Docker

Virtualization technology is a common concept and has different understandings in different fields. In the computational realm, it is generally referred to as computational virtualization (Computing Virtualization), or server virtualization, which is commonly said. The definitions on Wikipedia are as follows:

In computer technology, virtualization (virtualization) is a resource management technology, it is the computer's various physical resources, such as servers, networks, memory and storage, to be abstracted, transformed and rendered, breaking the non-cutting barriers between the physical structure, Enables users to apply these resources in a way that is better than the original configuration.

It can be seen that the core of virtualization is to abstract resources, the goal is often to run multiple systems or applications on the same host, thereby improving the utilization of system resources, while bringing cost reduction, ease of management and fault tolerance disaster and other benefits.

From the large class, virtualization technology can be divided into hardware-based virtualization and software-based virtualization. Among them, the real hardware-based virtualization technology is rare, a few such as the network card in the single-root multi-io virtualization (Virtualization andsharing Specification,sr-iov) and other technologies, is beyond the scope of this book's discussion.

Software-based virtualization can be divided into application virtualization and platform virtualization from the level of the object, which is typically the domain of virtual machine technology. Among them, the former generally refers to some analog equipment or wine such software. The latter can be subdivided into the following sub-categories:

Full virtualization. The virtual machine simulates the complete underlying hardware environment and the execution of privileged instructions without modification by the customer's operating system. such as VMware Workstation, VirtualBox, QEMU, and so on.

Hardware-assisted virtualization. Using hardware (primarily CPU) assisted support (currently available on the x86 architecture, including INTEL-VT and amd-v) to handle sensitive instructions for fully virtualized functions, the customer operating system does not need to be modified, such as Vmwareworkstation, Xen, Kvm.

Part of virtualization. Virtualization is only available for some hardware resources and needs to be modified by the guest operating system. Some of the earlier versions of virtualization technology now support only part of virtualization.

Hyper-Virtualization (paravirtualization). Some hardware interfaces are provided as software to the guest operating system, and the guest operating system needs to be modified, such as early Xen.

Operating system-level virtualization. The kernel isolates different processes by creating multiple virtual operating system instances (cores and libraries). Container-related technology is in this category.

As can be seen, Docker and other container technologies are part of the virtualization of the operating system.

Docker The virtualization approach has many advantages, which are inseparable from the characteristics of the operating system virtualization itself. Figure 1-1 below compares the differences between Docker and the common way of virtual machines.

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The traditional approach is to virtualize at the hardware level, requiring additional virtual machine management applications and virtual machine operating system tiers.

Docker containers are virtualized on the operating system level, and are directly reused on the local host's operating system, making them more lightweight.

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1.3 Virtualization and Docker