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Container Linux

Developer	CoreOS team, Red Hat
OS family	Linux (based on Gentoo Linux)
Working state	Discontinued
Source model	Open source
Initial release	October 3, 2013; 11 years ago (2013-10-03)
Latest release	2512.3.0 / May 22, 2020; 4 years ago (2020-05-22)
Latest preview	2513.2.0(Beta) / May 22, 2020; 4 years ago (2020-05-22) 2514.1.0(Alpha) / May 22, 2020; 4 years ago (2020-05-22)
Marketing target	Servers and clusters
Platforms	x86-64
Kernel type	Monolithic (Linux kernel)
License	Apache License 2.0
Succeeded by	Fedora CoreOS RHEL CoreOS Flatcar Container Linux
Official website	coreos.com

Container Linux (formerly CoreOS Linux) is a discontinued open-source lightweight operating system based on the Linux kernel and designed for providing infrastructure for clustered deployments. One of its focuses was scalability. As an operating system, Container Linux provided only the minimal functionality required for deploying applications inside software containers, together with built-in mechanisms for service discovery and configuration sharing.

Container Linux shares foundations with Gentoo Linux, ChromeOS, and ChromiumOS through a common software development kit (SDK). Container Linux adds new functionality and customization to this shared foundation to support server hardware and use cases. CoreOS was developed primarily by Alex Polvi, Brandon Philips, and Michael Marineau, with its major features available as a stable release.

The CoreOS team announced the end-of-life for Container Linux on May 26, 2020, offering Fedora CoreOS, and RHEL CoreOS as its replacement, both based on Red Hat Enterprise Linux.

Overview

Container Linux provides no package manager as a way for distributing payload applications, requiring instead all applications to run inside their containers. Serving as a single control host, a Container Linux instance uses the underlying operating-system-level virtualization features of the Linux kernel to create and configure multiple containers that perform as isolated Linux systems. That way, resource partitioning between containers is performed through multiple isolated userspace instances, instead of using a hypervisor and providing full-fledged virtual machines. This approach relies on the Linux kernel's cgroups and namespaces functionalities, which together provide abilities to limit, account and isolate resource usage (CPU, memory, disk I/O, etc.) for the collections of userspace processes.

Initially, Container Linux exclusively used Docker as a component providing an additional layer of abstraction and interface to the operating-system-level virtualization features of the Linux kernel, as well as providing a standardized format for containers that allows applications to run in different environments. In December 2014, CoreOS released and started to support rkt (initially released as Rocket) as an alternative to Docker, providing through it another standardized format of the application-container images, the related definition of the container runtime environment, and a protocol for discovering and retrieving container images. CoreOS provides rkt as an implementation of the so-called app container (appc) specification that describes the required properties of the application container image (ACI). CoreOS created appc and ACI as an independent committee-steered set of specifications aimed to become part of the vendor- and operating-system-independent Open Container Initiative, or OCI, initially named the Open Container Project (OCP) containerization standard, which was announced in June 2015.

Container Linux uses ebuild scripts from Gentoo Linux for automated compilation of its system components, and uses systemd as its primary init system, with tight integration between systemd and various Container Linux's internal mechanisms.

Updates distribution

Container Linux achieves additional security and reliability of its operating system updates by employing FastPatch as a dual-partition scheme for the read-only part of its installation, meaning that the updates are performed as a whole and installed onto a passive secondary boot partition that becomes active upon a reboot or kexec. This approach avoids possible issues arising from updating only certain parts of the operating system, ensures easy rollbacks to a known-to-be-stable version of the operating system, and allows each boot partition to be signed for additional security. The root partition and its root file system are automatically resized to fill all available disk-space upon reboots; while the root partition provides read-write storage space, the operating system itself is mounted read-only under /usr.

To ensure that only a certain part of the cluster reboots at once when the operating system updates are applied, preserving the resources required for running deployed applications, CoreOS provides locksmith as a reboot manager for Container Linux. Using locksmith, one can select between different update strategies that are determined by how the reboots are performed as the last step in applying updates; for example, one can configure how many cluster members are allowed to reboot simultaneously. Internally, locksmith operates as the locksmithd daemon that runs on cluster members, while the locksmithctl command-line utility manages configuration parameters. Locksmith is written in the Go language and distributed under the terms of the Apache License 2.0.

The updates distribution system employed by Container Linux is based on Google's open-source Omaha project, which provides a mechanism for rolling out updates and the underlying request–response protocol based on XML. Additionally, CoreOS provides CoreUpdate as a web-based dashboard for the management of cluster-wide updates. Operations available through CoreUpdate include assigning cluster members to different groups that share customized update policies, reviewing cluster-wide breakdowns of Container Linux versions, stopping and restarting updates, and reviewing recorded update logs. CoreUpdate also provides an HTTP-based API that allows its integration into third-party utilities or deployment systems.

Cluster infrastructure

Container Linux provides etcd, a daemon that runs across all computers in a cluster and provides a dynamic configuration registry, allowing various configuration data to be easily and reliably shared between the cluster members. Since the key–value data stored within etcd is automatically distributed and replicated with automated master election and consensus establishment using the Raft algorithm, all changes in stored data are reflected across the entire cluster, while the achieved redundancy prevents failures of single cluster members from causing data loss. Beside the configuration management, etcd also provides service discovery by allowing deployed applications to announce themselves and the services they offer. Communication with etcd is performed through an exposed REST-based API, which internally uses JSON on top of HTTP; the API may be used directly (through curl or wget, for example), or indirectly through etcdctl, which is a specialized command-line utility also supplied by CoreOS. etcd is also used in Kubernetes software.

Container Linux also provides the fleet cluster manager, which controls Container Linux's separate systemd instances at the cluster level. As of 2017, "fleet" is no longer actively developed and is deprecated in favor of Kubernetes. By using fleetd, Container Linux creates a distributed init system that ties together separate systemd instances and a cluster-wide etcd deployment; internally, fleetd daemon communicates with local systemd instances over D-Bus, and with the etcd deployment through its exposed API. Using fleetd allows the deployment of single or multiple containers cluster-wide, with more advanced options including redundancy, failover, deployment to specific cluster members, dependencies between containers, and grouped deployment of containers. A command-line utility called fleetctl is used to configure and monitor this distributed init system; internally, it communicates with the fleetd daemon using a JSON-based API on top of HTTP, which may also be used directly. When used locally on a cluster member, fleetctl communicates with the local fleetd instance over a Unix domain socket; when used from an external host, SSH tunneling is used with authentication provided through public SSH keys.

All of the above-mentioned daemons and command-line utilities (etcd, etcdctl, fleetd and fleetctl) are written in the Go language and distributed under the terms of the Apache License 2.0.

Deployment

When running on dedicated hardware, Container Linux can be either permanently installed on local storage, such as a hard disk drive (HDD) or solid-state drive (SSD), or booted remotely over a network using Preboot Execution Environment (PXE) in general, or iPXE as one of its implementations. CoreOS also supports deployments on various hardware virtualization platforms, including Amazon EC2, DigitalOcean, Google Compute Engine, Microsoft Azure, OpenStack, QEMU/KVM, Vagrant and VMware. Container Linux may also be installed on Citrix XenServer, noting that a "template" for CoreOS exists.

Container Linux can also be deployed through its commercial distribution called Tectonic, which additionally integrates Google's Kubernetes as a cluster management utility. As of April 2015, Tectonic is planned to be offered as beta software to select customers. Furthermore, CoreOS provides Flannel as a component, implementing an overlay network required primarily for the integration with Kubernetes.

As of February 2015, Container Linux supports only the x86-64 architecture.

Derivatives

Following its acquisition of CoreOS, Inc. in January 2018, Red Hat announced that it would be merging CoreOS Container Linux with Red Hat's Project Atomic to create a new operating system, Red Hat CoreOS, while aligning the upstream Fedora Project open source community around Fedora CoreOS, combining technologies from both predecessors.

On March 6, 2018, Kinvolk GmbH announced Flatcar Container Linux, a derivative of CoreOS Container Linux. This tracks the upstream CoreOS alpha, beta, and stable channel releases, with an experimental Edge release channel added in May 2019.

Reception

LWN.net reviewed CoreOS in 2014:

For those who are putting together large, distributed systems—web applications being a prime example—CoreOS would appear to have a lot of interesting functionality. It should allow applications of that type to grow and shrink as needed with demand, as well as provide a stable platform where upgrades are not a constant headache. For "massive server deployments", CoreOS, or something with many of the same characteristics, looks like the future.

See also

• Application virtualization – software technology that encapsulates application software from the operating system on which it is executed
• Comparison of application virtualization software – various portable and scripting language virtual machines
• Comparison of platform virtualization software – various emulators and hypervisors, which emulate the whole physical computers
• LXC (Linux Containers) – an environment for running multiple isolated Linux systems (containers) on a single Linux control host
• Operating-system-level virtualization implementations – based on operating system kernel's support for multiple isolated userspace instances
• Software as a service (SaaS) – a software licensing and delivery model that hosts the software centrally and licenses it on a subscription basis
• Virtualization – a general concept of providing virtual versions of computer hardware platforms, operating systems, storage devices, etc.

References

1. ^ "End-of-life announcement for CoreOS Container Linux". coreos.com. Retrieved August 16, 2020.
2. "coreos/manifest: Release v94.0.0 (Container Linux v94.0.0)". github.com. October 3, 2013. Retrieved September 22, 2014.
3. "CoreOS Container Linux Release Notes # Stable channel". coreos.com. May 22, 2020. Archived from the original on November 11, 2020. Retrieved May 22, 2020.
4. "CoreOS Container Linux Release Notes # Beta channel". coreos.com. May 22, 2020. Archived from the original on November 11, 2020. Retrieved May 22, 2020.
5. "CoreOS Container Linux Release Notes # Alpha channel". coreos.com. May 22, 2020. Archived from the original on November 11, 2020. Retrieved May 22, 2020.
6. ^ Timothy Prickett Morgan (February 15, 2015). "CoreOS Hyperscales Linux By Making It Invisible". nextplatform.com. Retrieved June 14, 2015.
7. "CoreOS Pilot Agreement". coreos.com. March 13, 2014. Archived from the original on September 12, 2014. Retrieved March 26, 2014.
8. ^ "coreos/etcd: etcd/LICENSE at master". github.com. July 31, 2013. Retrieved March 26, 2014.
9. "CoreOS Container Linux 2514.1.0 Documentation". coreos.com. January 21, 2021. Archived from the original on January 21, 2021. Retrieved January 21, 2021.
10. "CoreOS Linux is now Container Linux". coreos.com. Retrieved December 20, 2016.
11. ^ Libby Clark (September 9, 2013). "Brandon Philips: How the CoreOS Linux Distro Uses Cgroups". Linux.com. Archived from the original on February 22, 2014. Retrieved February 13, 2014.
12. ^ Cade Metz (August 21, 2013). "Linux Hackers Rebuild Internet From Silicon Valley Garage". Wired. Retrieved February 13, 2014.
13. ^ "CoreOS – a new approach to Linux-based server systems". itnews2day.com. August 22, 2013. Archived from the original on November 29, 2014. Retrieved March 26, 2014.
14. ^ "CoreOS documentation: Using CoreOS". coreos.com. Archived from the original on February 23, 2014. Retrieved February 13, 2014.
15. ^ "Building development images: Updating portage-stable ebuilds from Gentoo". coreos.com. Archived from the original on July 14, 2017. Retrieved May 24, 2016.
16. ^ "Distributions based on Gentoo". gentoo.org. March 25, 2016. Retrieved May 24, 2016.
17. Brian Harrington (July 8, 2014). "CoreOS: Anatomy of a CoreOS update". youtube.com. Rackspace. Retrieved July 25, 2014.
18. Alex Polvi (July 25, 2014). "CoreOS Stable Release". coreos.com. Retrieved August 28, 2014.
19. "CoreOS Release Notes". coreos.com. Archived from the original on November 11, 2020. Retrieved August 28, 2014.
20. Brandon Philips (January 28, 2015). "etcd 2.0 Release – First Major Stable Release". coreos.com. Retrieved June 14, 2015.
21. "Fedora CoreOS Documentation :: Fedora Docs Site". docs.fedoraproject.org. Retrieved August 16, 2020.
22. Jonathan Corbet (October 29, 2007). "Notes from a container". LWN.net. Retrieved July 3, 2016.
23. Jake Edge (November 19, 2014). "Control group namespaces". LWN.net. Retrieved July 3, 2016.
24. ^ "CoreOS documentation: Using Docker with CoreOS". coreos.com. Archived from the original on August 4, 2016. Retrieved June 14, 2015.
25. "Docker 0.9: Introducing execution drivers and libcontainer". docker.com. March 10, 2014. Retrieved January 20, 2015.
26. Libby Clark (January 30, 2015). "CoreOS Co-Founder Alex Polvi Talks Containers, Rocket vs. Docker, and More". Linux.com. Retrieved June 14, 2015.
27. Charles Babcock (February 20, 2015). "Rocket Containers: How CoreOS Plans To Challenge Docker". informationweek.com. Retrieved June 14, 2015.
28. Alex Polvi (December 1, 2014). "CoreOS is building a container runtime, rkt". coreos.com. Retrieved June 14, 2015.
29. ^ Josh Berkus (February 4, 2015). "New etcd, appc, and Rocket releases from CoreOS". LWN.net. Retrieved June 22, 2015.
30. ^ Josh Berkus (May 13, 2015). "CoreOS Fest and the world of containers, part 1". LWN.net. Retrieved June 22, 2015.
31. Nathan Willis (December 3, 2014). "The Rocket containerization system". LWN.net. Retrieved June 22, 2015.
32. McAllister, Neil (June 22, 2015). "Docker and chums unveil standards org for software containers". Data Centre. The Register. Retrieved January 19, 2017. Announced at the DockerCon conference in San Francisco on Monday, the Open Container Project (OCP) will maintain and develop a common container runtime and image format based in part on code and specs donated by Docker.
33. Frederic Lardinois (June 22, 2015). "Docker, CoreOS, Google, Microsoft, Amazon and others come together to develop common container standard". TechCrunch. Retrieved June 24, 2015.
34. "Industry Leaders Unite to Create Project for Open Container Standards". opencontainers.org. June 22, 2015. Archived from the original on August 13, 2015. Retrieved June 24, 2015.
35. Neil McAllister (July 22, 2015). "Open Container Project renames, says standard is just weeks away: Linux Foundation, Docker and friends opt for Open Container Initiative". The Register. Retrieved January 29, 2016.
36. "CoreOS documentation: Using systemd with CoreOS". coreos.com. Archived from the original on February 14, 2014. Retrieved February 13, 2014.
37. ^ "CoreOS documentation: Updates & patches". coreos.com. Archived from the original on February 14, 2014. Retrieved February 27, 2015.
38. ^ Phil Whelan (August 28, 2013). "Alex Polvi Explains CoreOS". activestate.com. Archived from the original on February 24, 2015. Retrieved May 7, 2015.
39. "CoreOS documentation: Adding disk space to your CoreOS machine". coreos.com. Retrieved February 27, 2015.
40. Alex Polvi (March 27, 2014). "Major Update: btrfs, Docker 0.9, add users, writable /etc, and more!". coreos.com. Retrieved February 27, 2015.
41. "Simple Introduction to CoreOS with CEO Alex Polvi and CTO Brandon Philips". centurylinklabs.com. June 6, 2014. Archived from the original on June 22, 2015. Retrieved June 22, 2015.
42. "CoreOS documentation: Update strategies". coreos.com. Retrieved April 17, 2015.
43. "coreos/locksmith: locksmith/README.md at master". github.com. February 1, 2015. Retrieved April 17, 2015.
44. "coreos/locksmith: locksmith/LICENSE at master". github.com. January 19, 2014. Retrieved April 17, 2015.
45. "Omaha – software installer and auto-updater for Windows". code.google.com. Retrieved October 11, 2014.
46. "Omaha Overview". omaha.googlecode.com. September 23, 2009. Archived from the original on May 6, 2009. Retrieved October 11, 2014.
47. "Package omaha". godoc.org. June 24, 2014. Retrieved July 4, 2014.
48. "CoreOS documentation: CoreUpdate". coreos.com. Retrieved July 4, 2014.
49. Mark Moudy (May 16, 2014). "CoreOS + Docker Development Environment Demo". github.com. Retrieved April 16, 2015.
50. ^ Jonathan Corbet (October 22, 2014). "Etcd and fleet". LWN.net. Retrieved June 22, 2015.
51. "CoreOS documentation: Using etcd with CoreOS". coreos.com. Retrieved February 13, 2014.
52. "CoreOS documentation: Getting started with etcd". coreos.com. Retrieved February 13, 2014.
53. Brandon Philips (January 15, 2014). "etcd @ GoSF". speakerdeck.com. Retrieved February 13, 2014.
54. Wood, Josh. "Container orchestration: Moving from fleet to Kubernetes". coreos..com. CoreOS.
55. Justin Ellingwood (September 12, 2014). "How To Use Fleet and Fleetctl to Manage your CoreOS Cluster". digitalocean.com. Retrieved June 22, 2015.
56. "CoreOS documentation: Launching containers with fleet". coreos.com. Retrieved April 3, 2014.
57. "CoreOS documentation: Using the client". coreos.com. Retrieved April 3, 2014.
58. "coreos/fleet: fleet/README.md at master". github.com. February 18, 2014. Retrieved April 3, 2014.
59. "coreos/fleet: fleet/Documentation/deployment-and-configuration.md at master (Deploying fleet)". github.com. April 14, 2015. Retrieved April 17, 2015.
60. "coreos/fleet: fleet/Documentation/api-v1.md (fleet API v1)". github.com. October 29, 2014. Retrieved April 17, 2015.
61. "coreos/fleet: fleet/LICENSE at master". github.com. February 6, 2014. Retrieved April 3, 2014.
62. "CoreOS documentation: Installing CoreOS to disk". coreos.com. Retrieved February 13, 2014.
63. "CoreOS documentation: Booting CoreOS via PXE". coreos.com. Retrieved February 13, 2014.
64. "CoreOS documentation: Booting CoreOS via iPXE". coreos.com. Retrieved February 13, 2014.
65. Alex Crawford (September 5, 2014). "CoreOS Image Now Available On DigitalOcean". coreos.com. Retrieved September 5, 2014.
66. Jack Clark (May 23, 2014). "Google brings futuristic Linux software CoreOS onto its cloud". The Register. Retrieved May 26, 2014.
67. Alex Crawford (October 20, 2014). "CoreOS Now Available On Microsoft Azure". coreos.com. Retrieved October 22, 2014.
68. Steven J. Vaughan-Nichols (April 6, 2015). "CoreOS is bringing Google's Kubernetes to the enterprise". ZDNet. Retrieved April 29, 2015.
69. Ben Kepes (April 6, 2015). "CoreOS And Google Make Their Defensive Plays, Is Docker The Victim?". Forbes. Retrieved April 29, 2015.
70. Eugene Yakubovich (August 28, 2014). "Introducing flannel: An etcd-backed overlay network for containers". coreos.com. Retrieved June 22, 2015.
71. "Tutorial on using CoreOS Flannel for Docker". slideshare.net. November 2014. Retrieved June 22, 2015.
72. Rosoff, Matt (January 30, 2018). "Red Hat pays $250 million for CoreOS, a start-up that sells Google-developed technology". CNBC. Retrieved June 6, 2019.
73. "Fedora CoreOS, Red Hat CoreOS, and the future of Container Linux | CoreOS". coreos.com. Retrieved June 6, 2019.
74. "Announcing the Flatcar Linux project | Kinvolk". kinvolk.io. March 6, 2018. Retrieved June 6, 2019.
75. "Introducing the Flatcar Linux Edge Channel | Kinvolk". kinvolk.io. May 15, 2019. Retrieved June 6, 2019.
76. CoreOS: A different kind of Linux distribution [LWN.net]

External links

• Official CoreOS and GitHub source code repositories: CoreOS , etcd , fleet , rkt and CoreOS-overlay
• CoreOS at DistroWatch
• First glimpse at CoreOS, September 3, 2013, by Sébastien Han
• CoreOS: Linux for the cloud and the datacenter, ZDNet, July 2, 2014, by Steven J. Vaughan-Nichols
• What's CoreOS? An existential threat to Linux vendors, InfoWorld, October 9, 2014, by Matt Asay
• Understanding CoreOS distributed architecture, March 4, 2015, a talk to Alex Polvi by Aaron Delp and Brian Gracely
• CoreOS fleet architecture, August 26, 2014, by Brian Waldon et al.
• Running CoreOS on Google Compute Engine, May 23, 2014
• CoreOS moves from Btrfs to Ext4 + OverlayFS, Phoronix, January 18, 2015, by Michael Larabel
• Containers and persistent data, LWN.net, May 28, 2015, by Josh Berkus

• Linux distributions
• Enterprise Linux distributions
• Linux containerization
• Containerization software
• Red Hat software
• Software using the Apache license
• Virtualization software for Linux