Container Linux

Last updated

Container Linux
Container Linux Logo.png
Developer CoreOS team, Red Hat
OS family Linux (based on Gentoo Linux)
Working stateDiscontinued [1]
Source model Open source
Initial releaseOctober 3, 2013;10 years ago (2013-10-03) [2]
Latest release 2512.3.0 [3] / May 22, 2020;4 years ago (2020-05-22)
Latest preview 2513.2.0 [4] (Beta) / May 22, 2020;4 years ago (2020-05-22)
2514.1.0 [5] (Alpha) / May 22, 2020;4 years ago (2020-05-22)
Marketing target Servers and clusters
Platforms x86-64 [6]
Kernel type Monolithic (Linux kernel)
License Apache License 2.0 [7] [8]
Succeeded byFedora CoreOS
RHEL CoreOS
Flatcar Container Linux
Official website coreos.com [9]

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. [10] [11] [12] [13] [14]

Contents

Container Linux shares foundations with Gentoo Linux, [15] [16] 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. [13] [17] :7:02 CoreOS was developed primarily by Alex Polvi, Brandon Philips, and Michael Marineau, [12] with its major features available as a stable release. [18] [19] [20]

The CoreOS team announced the end-of-life for Container Linux on May 26, 2020, [1] offering Fedora CoreOS, [21] 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, [22] [23] which together provide abilities to limit, account and isolate resource usage (CPU, memory, disk I/O, etc.) for the collections of userspace processes. [11] [14] [24]

Initially, Container Linux exclusively used Docker as a component providing an additional layer of abstraction and interface [25] 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. [11] [24] 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. [26] [27] [28] [29] 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 [30] [31] 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, [32] which was announced[ by whom? ] in June 2015. [33] [34] [35]

Container Linux uses ebuild scripts from Gentoo Linux for automated compilation of its system components, [15] [16] and uses systemd as its primary init system, with tight integration between systemd and various Container Linux's internal mechanisms. [11] [36]

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. [11] [14] [37] 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. [38] [39] [40]

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. [41] 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. [42] [43] Locksmith is written in the Go language and distributed under the terms of the Apache License 2.0. [44]

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. [6] [45] [46] 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. [37] [47] [48]

Cluster infrastructure

A high-level illustration of the CoreOS cluster architecture CoreOS Architecture Diagram.svg
A high-level illustration of the CoreOS cluster architecture

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. [6] [38] 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. [29] [50] 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. [11] [14] [51] [52] [53] 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. [54] By using fleetd, Container Linux creates a distributed init system that ties together separate systemd instances and a cluster-wide etcd deployment; [50] 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; [55] 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. [56] [57] [58] [59] [60]

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. [8] [61]

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), [62] or booted remotely over a network using Preboot Execution Environment (PXE) in general, or iPXE as one of its implementations. [63] [64] CoreOS also supports deployments on various hardware virtualization platforms, including Amazon EC2, DigitalOcean, Google Compute Engine, Microsoft Azure, OpenStack, QEMU/KVM, Vagrant and VMware. [14] [65] [66] [67] 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. [30] [68] [69] Furthermore, CoreOS provides Flannel as a component, implementing an overlay network required primarily for the integration with Kubernetes. [30] [70] [71]

As of February 2015, Container Linux supports only the x86-64 architecture. [6]

Derivatives

Following its acquisition of CoreOS, Inc. [72] in January 2018, Red Hat announced [73] 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 [74] 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. [75]

Reception

LWN.net reviewed CoreOS in 2014: [76]

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

Related Research Articles

seccomp is a computer security facility in the Linux kernel. seccomp allows a process to make a one-way transition into a "secure" state where it cannot make any system calls except exit , sigreturn , read and write to already-open file descriptors. Should it attempt any other system calls, the kernel will either just log the event or terminate the process with SIGKILL or SIGSYS. In this sense, it does not virtualize the system's resources but isolates the process from them entirely.

OS-level virtualization is an operating system (OS) virtualization paradigm in which the kernel allows the existence of multiple isolated user space instances, called containers, zones, virtual private servers (OpenVZ), partitions, virtual environments (VEs), virtual kernels, or jails. Such instances may look like real computers from the point of view of programs running in them. A computer program running on an ordinary operating system can see all resources of that computer. However, programs running inside of a container can only see the container's contents and devices assigned to the container.

The following is about virtualization development. In computing, virtualization is the use of a computer to simulate another computer. Through virtualization, a host simulates a guest by exposing virtual hardware devices, which may be done through software or by allowing access to a physical device connected to the machine.

<span class="mw-page-title-main">Oracle Linux</span> Linux distribution by Oracle

Oracle Linux is a Linux distribution packaged and freely distributed by Oracle, available partially under the GNU General Public License since late 2006. It is compiled from Red Hat Enterprise Linux (RHEL) source code, replacing Red Hat branding with Oracle's. It is also used by Oracle Cloud and Oracle Engineered Systems such as Oracle Exadata and others.

Ceph is a free and open-source software-defined storage platform that provides object storage, block storage, and file storage built on a common distributed cluster foundation. Ceph provides distributed operation without a single point of failure and scalability to the exabyte level. Since version 12 (Luminous), Ceph does not rely on any other conventional filesystem and directly manages HDDs and SSDs with its own storage backend BlueStore and can expose a POSIX filesystem.

<span class="mw-page-title-main">Linux kernel</span> Free Unix-like operating system kernel

The Linux kernel is a free and open source, UNIX-like kernel that is used in many computer systems worldwide. The kernel was created by Linus Torvalds in 1991 and was soon adopted as the kernel for the GNU operating system (OS) which was created to be a free replacement for Unix. Since the late 1990s, it has been included in many operating system distributions, many of which are called Linux. One such Linux kernel operating system is Android which is used in many mobile and embedded devices.

<span class="mw-page-title-main">LXC</span> Operating system-level virtualization for Linux

Linux Containers (LXC) is an operating system-level virtualization method for running multiple isolated Linux systems (containers) on a control host using a single Linux kernel.

systemd Suite of system components for Linux

systemd is a software suite that provides an array of system components for Linux operating systems. The main aim is to unify service configuration and behavior across Linux distributions. Its primary component is a "system and service manager" — an init system used to bootstrap user space and manage user processes. It also provides replacements for various daemons and utilities, including device management, login management, network connection management, and event logging. The name systemd adheres to the Unix convention of naming daemons by appending the letter d. It also plays on the term "System D", which refers to a person's ability to adapt quickly and improvise to solve problems.

cgroups is a Linux kernel feature that limits, accounts for, and isolates the resource usage of a collection of processes.

<span class="mw-page-title-main">Lennart Poettering</span> German software engineer

Lennart Poettering is a German software engineer working for Microsoft and the original author of PulseAudio, Avahi and systemd.

<span class="mw-page-title-main">OpenShift</span> Cloud computing software

OpenShift is a family of containerization software products developed by Red Hat. Its flagship product is the OpenShift Container Platform — a hybrid cloud platform as a service built around Linux containers orchestrated and managed by Kubernetes on a foundation of Red Hat Enterprise Linux. The family's other products provide this platform through different environments: OKD serves as the community-driven upstream, Several deployment methods are available including self-managed, cloud native under ROSA, ARO and RHOIC on AWS, Azure, and IBM Cloud respectively, OpenShift Online as software as a service, and OpenShift Dedicated as a managed service.

Docker is a set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called containers. The service has both free and premium tiers. The software that hosts the containers is called Docker Engine. It was first released in 2013 and is developed by Docker, Inc.

Namespaces are a feature of the Linux kernel that partition kernel resources such that one set of processes sees one set of resources, while another set of processes sees a different set of resources. The feature works by having the same namespace for a set of resources and processes, but those namespaces refer to distinct resources. Resources may exist in multiple namespaces. Examples of such resources are process IDs, host-names, user IDs, file names, some names associated with network access, and Inter-process communication.

Kubernetes is an open-source container orchestration system for automating software deployment, scaling, and management. Originally designed by Google, the project is now maintained by a worldwide community of contributors, and the trademark is held by the Cloud Native Computing Foundation.

<span class="mw-page-title-main">Mirantis</span> Cloud computing software and services company

Mirantis Inc. is a Campbell, California, based B2B open source cloud computing software and services company. Its primary container and cloud management products, part of the Mirantis Cloud Native Platform suite of products, are Mirantis Container Cloud and Mirantis Kubernetes Engine. The company focuses on the development and support of container and cloud infrastructure management platforms based on Kubernetes and OpenStack. The company was founded in 1999 by Alex Freedland and Boris Renski. It was one of the founding members of the OpenStack Foundation, a non-profit corporate entity established in September, 2012 to promote OpenStack software and its community. Mirantis has been an active member of the Cloud Native Computing Foundation since 2016.

<span class="mw-page-title-main">Snap (software)</span> Software deployment system for Linux by Canonical

Snap is a software packaging and deployment system developed by Canonical for operating systems that use the Linux kernel and the systemd init system. The packages, called snaps, and the tool for using them, snapd, work across a range of Linux distributions and allow upstream software developers to distribute their applications directly to users. Snaps are self-contained applications running in a sandbox with mediated access to the host system. Snap was originally released for cloud applications but was later ported to also work for Internet of Things devices and desktop applications.

casync is a Linux software utility designed to distribute frequently-updated file system images over the Internet.

gVisor Linux software project developed by Google

gVisor is a container sandbox developed by Google that focuses on security, efficiency and ease of use. gVisor implements around 200 of the Linux system calls in userspace, for additional security compared to Docker containers that run directly on top of the Linux kernel and are isolated with namespaces. Unlike the Linux kernel, gVisor is written in the memory-safe programming language Go to prevent common pitfalls which frequently occur in software written in C.

The Cloud Native Computing Foundation (CNCF) is a Linux Foundation project that was started in 2015 to help advance container technology and align the tech industry around its evolution.

<span class="mw-page-title-main">Clear Linux OS</span> Linux distribution by Intel

Clear Linux OS is a Linux distribution, developed and maintained on Intel's 01.org open-source platform, and optimized for Intel's microprocessors with an emphasis on performance and security. Its optimizations are also effective on AMD systems. Clear Linux OS follows a rolling release model. Clear Linux OS is not intended to be a general-purpose Linux distribution; it is designed to be used by IT professionals for DevOps, AI application development, cloud computing, and containers.

References

  1. 1 2 "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. 1 2 3 4 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. 1 2 "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. 1 2 3 4 5 6 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. 1 2 Cade Metz (August 21, 2013). "Linux Hackers Rebuild Internet From Silicon Valley Garage". Wired . Retrieved February 13, 2014.
  13. 1 2 "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. 1 2 3 4 5 "CoreOS documentation: Using CoreOS". coreos.com. Archived from the original on February 23, 2014. Retrieved February 13, 2014.
  15. 1 2 "Building development images: Updating portage-stable ebuilds from Gentoo". coreos.com. Archived from the original on July 14, 2017. Retrieved May 24, 2016.
  16. 1 2 "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. 1 2 "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. 1 2 Josh Berkus (February 4, 2015). "New etcd, appc, and Rocket releases from CoreOS". LWN.net . Retrieved June 22, 2015.
  30. 1 2 3 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. 1 2 "CoreOS documentation: Updates & patches". coreos.com. Archived from the original on February 14, 2014. Retrieved February 27, 2015.
  38. 1 2 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. 1 2 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]