{"id":6898,"date":"2020-10-22T09:12:14","date_gmt":"2020-10-22T13:12:14","guid":{"rendered":"https:\/\/www.lpi.org\/xen-virtualization-and-cloud-computing-04-containers-openstack-and-other-related\/"},"modified":"2023-05-10T04:27:46","modified_gmt":"2023-05-10T08:27:46","slug":"xen-virtualization-and-cloud-computing-04-containers-openstack-and-other-related","status":"publish","type":"post","link":"https:\/\/www.lpi.org\/it\/blog\/2020\/10\/22\/xen-virtualization-and-cloud-computing-04-containers-openstack-and-other-related\/","title":{"rendered":"Xen Virtualization and Cloud Computing #04: Containers, OpenStack, and Other Related Platforms"},"content":{"rendered":"

Previous articles in this series introduced virtualization, discussed how Xen\u2019s architecture provides it, and covered interesting Xen features. This article looks at some other platforms with which Xen interacts: containers and OpenStack.<\/p>\n

Virtualization, containers\u2014or both?<\/h3>\n

Containers are a mechanism for isolating processes, similar to virtualization. With Docker<\/a> and Kubernetes<\/a>, containers have became popular over the past decade and are considered by some people to be competition for virtualization. So I\u2019ll discuss the relationship briefly.<\/p>\n

Container technology was born in 1979 with Unix version 7 and its chroot feature. A command called chroot, which stands for \u201cchange root directory,\u201d isolates a process and restricts its access to a specific directory. For instance, if you change a process\u2019s root to \/tmp\/local23<\/em>, and the process tries to run \/usr\/bin\/python3<\/em>, it will actually run \/tmp\/local23\/usr\/bin\/python3<\/em>.<\/p>\n

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This technology was hard to use and didn\u2019t seem to have much application, so it was mostly forgotten. But in 2000s, the idea became more popular with the introduction of FreeBSD Jails<\/a>. This mechanism partitions a FreeBSD into several independent mini-systems that share the same kernel. Sun Microsystems entered the container era in 2004 with Solaris Containers (also called Solaris Zones<\/a>), which combined system resource controls with boundary separation.<\/p>\n

In 2001, this jail system was introduced into Linux with Linux Vserver<\/a>, and in 2005, with OpenVZ<\/a>, this technology was added to the Linux kernel. \u00a0In 2006, Linux introduced control groups (cgroups<\/a>) with accounts, resource limits, and isolation of resources such as CPU and memory. Two Google engineers, Paul Menage and Rohit Seth, extended the concept with a mechanism called \u201cprocess containers.\u201d Finally, in 2008, LXC<\/a> (Linux Containers) was introduced as virtualization at the operating system level. The reliability and stability of LXC persuaded developers to build other container technologies on it. The first of these was Warden in 2011, superseded by Docker in 2013.<\/p>\n

Docker was a revolution in container technology. It offers a GUI interface and is easy to use. After Docker, another technology with the name rkt<\/a> (pronounced Rocket) tried to improve on some of the gaps in Docker.<\/p>\n

Basically, container technology is a method of packaging an application so it can run with isolated dependencies. Whereas virtual machines run their own kernels and look like complete computer systems, containers run individual processes and share the host OS through the help of container engine. Containers are lightweight and deploying them is now fast and easy. They are highly suitable for short-term applications, and when the users\u2019 biggest priority is to run the maximum number of applications on a minimal number of servers.<\/p>\n

Figure 5 compares containers and virtualization.<\/p>\n

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Figure 5. Architecture of virtualization and containers<\/figcaption><\/figure>\n<\/p>\n

Despite the benefits of the containers, they also have disadvantages. I\u2019ll mention some here:<\/p>\n