CoreOS

CoreOS
CoreOS logo
OS family Unix-like
Working state In development
Source model Open source
Initial release October 3, 2013 (2013-10-03)[1]
Latest release 1097.0.0[2] / July 2, 2016 (2016-07-02)
Latest preview 1095.1.0[3] / June 30, 2016 (2016-06-30)
Marketing target Servers and clusters
Platforms x86-64[4]
Kernel type Monolithic (Linux kernel)
License Apache License 2.0[5][6]
Official website coreos.com

CoreOS is an open-source lightweight operating system based on the Linux kernel and designed for providing infrastructure to clustered deployments, while focusing on automation, ease of application deployment, security, reliability and scalability. As an operating system, CoreOS provides only the minimal functionality required for deploying applications inside software containers, together with built-in mechanisms for service discovery and configuration sharing.[7][8][9][10]

CoreOS shares the foundations with Gentoo Linux,[11][12] Chrome OS and Chromium OS, by the means of using their common software development kit (SDK) as a base while adding new functionality and customizing it to support hardware used in servers.[9][13]:7:02 As of January 2015, CoreOS is actively developed, primarily by Alex Polvi, Brandon Philips and Michael Marineau,[8] with its major features available as a stable release.[14][15][16]

Overview

CoreOS 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 CoreOS 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,[17][18] which together provide abilities to limit, account and isolate resource usage (CPU, memory, disk I/O, etc.) for the collections of userspace processes.[7][10][19]

Initially, CoreOS exclusively used Docker as a component providing an additional layer of abstraction and interface[20] 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.[7][19] 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, related definition of the container runtime environment, and a protocol for discovering and retrieving container images.[21][22][23][24] CoreOS provides rkt as an implementation of the so-called app container (appc) specification that describes required properties of the application container image (ACI); CoreOS initiated appc and ACI as an independent committee-steered set of specifications,[25][26] aiming at having them become part of the vendor- and operating-system-independent Open Container Initiative (initially named Open Container Project) containerization standard, which was announced in June 2015.[27][28][29]

CoreOS uses ebuild scripts from Gentoo Linux for automated compilation of its system components,[11][12] and uses systemd as its primary init system with tight integration between systemd and various CoreOS' internal mechanisms.[7][30]

Updates distribution

CoreOS 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.[7][10][31] 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.[32][33][34]

To ensure that only a certain part of the cluster reboots at once when the operating system updates are applied, preserving that way the resources required for running deployed applications, CoreOS provides locksmith as a reboot manager.[35] Using locksmith, it is possible to select between different update strategies that are determined by how the reboots are performed as the last step in applying updates; for example, it may be configured 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.[36][37] locksmith is written in the Go language and distributed under the terms of the Apache License 2.0.[38]

The updates distribution system employed by CoreOS 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.[4][39][40] 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 CoreOS versions, stopping and restarting updates, and reviewing recorded update logs. CoreUpdate also provides a HTTP-based API that allows its integration into third-party utilities or deployment systems.[31][41][42]

Cluster infrastructure

A high-level illustration of the CoreOS cluster architecture[43]

CoreOS 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.[4][32] 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.[24][44] 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.[7][10][45][46][47]

CoreOS also provides so-called fleet functionality, based on the fleetd cluster manager daemon that controls CoreOS' separate systemd instances at the cluster level. By using fleetd, CoreOS creates a distributed init system that ties together separate systemd instances and a cluster-wide etcd deployment;[44] internally, fleetd daemon communicates with local systemd instances over D-Bus, and with the etcd deployment through its exposed API. Using fleetd allows single or multiple containers to be deployed 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;[48] 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.[49][50][51][52][53]

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.[6][54]

Deployment

When running on dedicated hardware, CoreOS can be either permanently installed to local storage, such as a hard disk drive (HDD) or solid-state drive (SSD),[55] or booted remotely over a network using Preboot Execution Environment (PXE) in general, or iPXE as one of its implementations.[56][57] CoreOS also supports deployments on various hardware virtualization platforms, including Amazon EC2, DigitalOcean, Google Compute Engine, Microsoft Azure, OpenStack, QEMU/KVM, Vagrant and VMware.[10][58][59][60]

CoreOS 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.[25][61][62] Furthermore, CoreOS provides Flannel as a component implementing an overlay network required primarily for the integration with Kubernetes.[25][63][64]

As of February 2015, CoreOS supports only the x86-64 architecture.[4]

See also

References

  1. ↑ "coreos/manifest: Release v94.0.0 (CoreOS v94.0.0)". github.com. October 3, 2013. Retrieved September 22, 2014.
  2. ↑ "coreos/manifest: Release v1097.0.0 (CoreOS v1097.0.0)". github.com. July 2, 2016. Retrieved July 3, 2016.
  3. ↑ "coreos/manifest: Release v1095.1.0 (CoreOS v1095.1.0)". github.com. June 30, 2016. Retrieved July 3, 2016.
  4. 1 2 3 4 Timothy Prickett Morgan (February 15, 2015). "CoreOS Hyperscales Linux By Making It Invisible". nextplatform.com. Retrieved June 14, 2015.
  5. ↑ "CoreOS Pilot Agreement". coreos.com. March 13, 2014. Retrieved March 26, 2014.
  6. 1 2 "coreos/etcd: etcd/LICENSE at master". github.com. July 31, 2013. Retrieved March 26, 2014.
  7. 1 2 3 4 5 6 Libby Clark (September 9, 2013). "Brandon Philips: How the CoreOS Linux Distro Uses Cgroups". Linux.com. Retrieved February 13, 2014.
  8. 1 2 Cade Metz (August 21, 2013). "Linux Hackers Rebuild Internet From Silicon Valley Garage". Wired. Retrieved February 13, 2014.
  9. 1 2 "CoreOS – a new approach to Linux-based server systems". itnews2day.com. August 22, 2013. Retrieved March 26, 2014.
  10. 1 2 3 4 5 "CoreOS documentation: Using CoreOS". coreos.com. Retrieved February 13, 2014.
  11. 1 2 "Building development images: Updating portage-stable ebuilds from Gentoo". coreos.com. Retrieved May 24, 2016.
  12. 1 2 "Distributions based on Gentoo". gentoo.org. March 25, 2016. Retrieved May 24, 2016.
  13. ↑ Brian Harrington (July 8, 2014). "CoreOS: Anatomy of a CoreOS update". youtube.com. Rackspace. Retrieved July 25, 2014.
  14. ↑ Alex Polvi (July 25, 2014). "CoreOS Stable Release". coreos.com. Retrieved August 28, 2014.
  15. ↑ "CoreOS Release Notes". coreos.com. Retrieved August 28, 2014.
  16. ↑ Brandon Philips (January 28, 2015). "etcd 2.0 Release – First Major Stable Release". coreos.com. Retrieved June 14, 2015.
  17. ↑ Jonathan Corbet (October 29, 2007). "Notes from a container". LWN.net. Retrieved July 3, 2016.
  18. ↑ Jake Edge (November 19, 2014). "Control group namespaces". LWN.net. Retrieved July 3, 2016.
  19. 1 2 "CoreOS documentation: Using Docker with CoreOS". coreos.com. Retrieved June 14, 2015.
  20. ↑ "Docker 0.9: Introducing execution drivers and libcontainer". docker.com. March 10, 2014. Retrieved January 20, 2015.
  21. ↑ Libby Clark (January 30, 2015). "CoreOS Co-Founder Alex Polvi Talks Containers, Rocket vs. Docker, and More". Linux.com. Retrieved June 14, 2015.
  22. ↑ Charles Babcock (February 20, 2015). "Rocket Containers: How CoreOS Plans To Challenge Docker". informationweek.com. Retrieved June 14, 2015.
  23. ↑ Alex Polvi (December 1, 2014). "CoreOS is building a container runtime, rkt". coreos.com. Retrieved June 14, 2015.
  24. 1 2 Josh Berkus (February 4, 2015). "New etcd, appc, and Rocket releases from CoreOS". LWN.net. Retrieved June 22, 2015.
  25. 1 2 3 Josh Berkus (May 13, 2015). "CoreOS Fest and the world of containers, part 1". LWN.net. Retrieved June 22, 2015.
  26. ↑ Nathan Willis (December 3, 2014). "The Rocket containerization system". LWN.net. Retrieved June 22, 2015.
  27. ↑ Frederic Lardinois (June 22, 2015). "Docker, CoreOS, Google, Microsoft, Amazon and others come together to develop common container standard". TechCrunch. Retrieved June 24, 2015.
  28. ↑ "Industry Leaders Unite to Create Project for Open Container Standards". opencontainers.org. June 22, 2015. Retrieved June 24, 2015.
  29. ↑ 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.
  30. ↑ "CoreOS documentation: Using systemd with CoreOS". coreos.com. Retrieved February 13, 2014.
  31. 1 2 "CoreOS documentation: Updates & patches". coreos.com. Retrieved February 27, 2015.
  32. 1 2 Phil Whelan (August 28, 2013). "Alex Polvi Explains CoreOS". activestate.com. Retrieved May 7, 2015.
  33. ↑ "CoreOS documentation: Adding disk space to your CoreOS machine". coreos.com. Retrieved February 27, 2015.
  34. ↑ Alex Polvi (March 27, 2014). "Major Update: btrfs, Docker 0.9, add users, writable /etc, and more!". coreos.com. Retrieved February 27, 2015.
  35. ↑ "Simple Introduction to CoreOS with CEO Alex Polvi and CTO Brandon Philips". centurylinklabs.com. June 6, 2014. Retrieved June 22, 2015.
  36. ↑ "CoreOS documentation: Update strategies". coreos.com. Retrieved April 17, 2015.
  37. ↑ "coreos/locksmith: locksmith/README.md at master". github.com. February 1, 2015. Retrieved April 17, 2015.
  38. ↑ "coreos/locksmith: locksmith/LICENSE at master". github.com. January 19, 2014. Retrieved April 17, 2015.
  39. ↑ "Omaha – software installer and auto-updater for Windows". code.google.com. Retrieved October 11, 2014.
  40. ↑ "Omaha Overview". omaha.googlecode.com. September 23, 2009. Retrieved October 11, 2014.
  41. ↑ "Package omaha". godoc.org. June 24, 2014. Retrieved July 4, 2014.
  42. ↑ "CoreOS documentation: CoreUpdate". coreos.com. Retrieved July 4, 2014.
  43. ↑ Mark Moudy (May 16, 2014). "CoreOS + Docker Development Environment Demo". github.com. Retrieved April 16, 2015.
  44. 1 2 Jonathan Corbet (October 22, 2014). "Etcd and fleet". LWN.net. Retrieved June 22, 2015.
  45. ↑ "CoreOS documentation: Using etcd with CoreOS". coreos.com. Retrieved February 13, 2014.
  46. ↑ "CoreOS documentation: Getting started with etcd". coreos.com. Retrieved February 13, 2014.
  47. ↑ Brandon Philips (January 15, 2014). "etcd @ GoSF". speakerdeck.com. Retrieved February 13, 2014.
  48. ↑ Justin Ellingwood (September 12, 2014). "How To Use Fleet and Fleetctl to Manage your CoreOS Cluster". digitalocean.com. Retrieved June 22, 2015.
  49. ↑ "CoreOS documentation: Launching containers with fleet". coreos.com. Retrieved April 3, 2014.
  50. ↑ "CoreOS documentation: Using the client". coreos.com. Retrieved April 3, 2014.
  51. ↑ "coreos/fleet: fleet/README.md at master". github.com. February 18, 2014. Retrieved April 3, 2014.
  52. ↑ "coreos/fleet: fleet/Documentation/deployment-and-configuration.md at master (Deploying fleet)". github.com. April 14, 2015. Retrieved April 17, 2015.
  53. ↑ "coreos/fleet: fleet/Documentation/api-v1.md (fleet API v1)". github.com. October 29, 2014. Retrieved April 17, 2015.
  54. ↑ "coreos/fleet: fleet/LICENSE at master". github.com. February 6, 2014. Retrieved April 3, 2014.
  55. ↑ "CoreOS documentation: Installing CoreOS to disk". coreos.com. Retrieved February 13, 2014.
  56. ↑ "CoreOS documentation: Booting CoreOS via PXE". coreos.com. Retrieved February 13, 2014.
  57. ↑ "CoreOS documentation: Booting CoreOS via iPXE". coreos.com. Retrieved February 13, 2014.
  58. ↑ Alex Crawford (September 5, 2014). "CoreOS Image Now Available On DigitalOcean". coreos.com. Retrieved September 5, 2014.
  59. ↑ Jack Clark (May 23, 2014). "Google brings futuristic Linux software CoreOS onto its cloud". The Register. Retrieved May 26, 2014.
  60. ↑ Alex Crawford (October 20, 2014). "CoreOS Now Available On Microsoft Azure". coreos.com. Retrieved October 22, 2014.
  61. ↑ Steven J. Vaughan-Nichols (April 6, 2015). "CoreOS is bringing Google's Kubernetes to the enterprise". ZDNet. Retrieved April 29, 2015.
  62. ↑ Ben Kepes (April 6, 2015). "CoreOS And Google Make Their Defensive Plays, Is Docker The Victim?". Forbes. Retrieved April 29, 2015.
  63. ↑ Eugene Yakubovich (August 28, 2014). "Introducing flannel: An etcd-backed overlay network for containers". coreos.com. Retrieved June 22, 2015.
  64. ↑ "Tutorial on using CoreOS Flannel for Docker". slideshare.net. November 2014. Retrieved June 22, 2015.
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