From the Captain to the Dockers

Google's operating system Chrome OS [19] inspired the design of Container Linux. The launch took place in fall 2013 under version 2 of the Apache license. Container Linux builds on components such as the kernel and systemd, so the respective licences apply. The resource consumption proves to be quite low: around 30 and 140MB (Figure 2) for the (virtual) hard disk and in memory.

Figure 2: Container Linux proves to be extremely frugal with resources, including disk space and memory.

Container Linux dispenses with a package manager for several reasons. Because the operating system only provides a few basic functions, the number of installed applications were decreased, so the need for a tool to manage them disappeared.

Container Linux ruthlessly replaces the entire /usr directory instead of individual files (Figure 3). The main work is handled by Linux containers à la Docker [20], or Rkt [21], etcd [22], and Kubernetes [23]. In earlier versions, Fleet was also on board, but CoreOS recently dropped it [24]. The name change for the Linux distribution was accompanied by complete orientation on Kubernetes as the orchestration software, making its transformation to managing containers complete.

Figure 3: Container Linux in normal operation does not make changes to /usr; this even applies to some files in /etc.

Channel Workers

A little logistical information can help get you started working with Container Linux. The developers manage three channels: stable, beta, and alpha. Seasoned Linux veterans are already familiar with this idea from Debian. The developers implement bug fixes or new features for Container Linux in the alpha channel first. Once no (more) errors occur, the changes move to the beta branch, and promotion to the stable channel follows the same principle.

One popular way of versioning Container Linux might be to derive the version from components such as the kernel, etcd, or the Docker version, but the project behind the technology has opted for a different, somewhat obscure approach. The version number is the number of days that have elapsed since the epoch of Container Linux – July 1, 2013. The first version was released October 3, 2013 and was thus numbered 94 as a result [25]. Because the developers also follow a semantic versioning scheme, it was dubbed 94.0.0. New features or bug fixes that are backward compatible thus do not lead to an increase in the number of days.

Bookcase OS

CirrOS and Container Linux still quite clearly show their descent from classic Linux distributions. The server or desktop versions of Linux were the starting point for these leaner, customized versions.

The question of how much operating system is still needed in the cloud can be viewed from a different perspective. MirageOS [26], according to the developers, traces its beginnings back to 2009. The project first offered it to the general public as version 1.0 in December 2013. However, MirageOS is less an operating system and more of a library.

The library operating system harks back to the 1990s [27] [28]. The concept is radical: The application is at the same time the operating system core to be booted – that is, more or less the complete virtual server. Many tasks of a traditional kernel fall away or are reduced significantly, such as managing the network or memory, opening up new options with respect to the choice of programming language.

MirageOS delegates many tasks to the underlying layer. Normally this is a hypervisor, but it can also be a traditional Linux. In the current version 3, MirageOS supports Xen [29] and KVM [30]. On the hardware side, the available architectures are x86 and ARM, where MirageOS is released under the Internet Systems Consortium (ISC) license [31]. Organizationally, the cloud operating system is listed as one of the incubator projects within Xen [32].