Docker (software)

This article is about the virtualization software. For the desktop icon docker, see Dock (computing). For other uses, see Docker (disambiguation).

Docker

Original author(s)	Solomon Hykes
Developer(s)	Docker, Inc.
Initial release	13 March 2013 (2013-03-13)
Stable release	1.11.1 / 26 April 2016 (2016-04-26)
Written in	Go
Operating system	Linux
Platform	x86-64 with modern Linux kernel
Type	Operating system-level virtualization
License	Apache License 2.0
Website	www.docker.com

Docker is an open-source project that automates the deployment of applications inside software containers. Quote of features from docker web page:

Docker containers wrap up a piece of software in a complete filesystem that contains everything it needs to run: code, runtime, system tools, system libraries – anything you can install on a server. This guarantees that it will always run the same, regardless of the environment it is running in.

Docker provides an additional layer of abstraction and automation of operating-system-level virtualization on Linux. Docker uses the resource isolation features of the Linux kernel such as cgroups and kernel namespaces, and a union-capable file system such as aufs and others to allow independent "containers" to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines.

The Linux kernel's support for namespaces mostly isolates an application's view of the operating environment, including process trees, network, user IDs and mounted file systems, while the kernel's cgroups provide resource limiting, including the CPU, memory, block I/O and network. Since version 0.9, Docker includes the libcontainer library as its own way to directly use virtualization facilities provided by the Linux kernel, in addition to using abstracted virtualization interfaces via libvirt, LXC (Linux Containers) and systemd-nspawn.

Overview

Docker can use different interfaces to access virtualization features of the Linux kernel.

As actions are done to a Docker base image, union file system layers are created and documented, such that each layer fully describes how to recreate an action. This strategy enables Docker's lightweight images, as only layer updates need to be propagated (compared to full VMs, for example).

According to industry analyst firm 451 Research, "Docker is a tool that can package an application and its dependencies in a virtual container that can run on any Linux server. This helps enable flexibility and portability on where the application can run, whether on premises, public cloud, private cloud, bare metal, etc."

Docker implements a high-level API to provide lightweight containers that run processes in isolation.

Building on top of facilities provided by the Linux kernel (primarily cgroups and namespaces), a Docker container, unlike a virtual machine, does not require or include a separate operating system. Instead, it relies on the kernel's functionality and uses resource isolation (CPU, memory, block I/O, network, etc.) and separate namespaces to isolate the application's view of the operating system. Docker accesses the Linux kernel's virtualization features either directly using the libcontainer library, which is available as of Docker 0.9, or indirectly via libvirt, LXC (Linux Containers) or systemd-nspawn.

By using containers, resources can be isolated, services restricted, and processes provisioned to have an almost completely private view of the operating system with their own process ID space, file system structure, and network interfaces. Multiple containers share the same kernel, but each container can be constrained to only use a defined amount of resources such as CPU, memory and I/O.

Using Docker to create and manage containers may simplify the creation of highly distributed systems by allowing multiple applications, worker tasks and other processes to run autonomously on a single physical machine or across multiple virtual machines. This allows the deployment of nodes to be performed as the resources become available or when more nodes are needed, allowing a platform as a service (PaaS)-style of deployment and scaling for systems like Apache Cassandra, MongoDB or Riak. Docker also simplifies the creation and operation of task or workload queues and other distributed systems.

Integration

Docker can be integrated into various infrastructure tools, including Amazon Web Services, Ansible, CFEngine, Chef, Google Cloud Platform, IBM Bluemix, Jelastic, Jenkins, Microsoft Azure, OpenStack Nova, OpenSVC, HPE Helion Stacakto, Puppet, Salt, Vagrant, and VMware vSphere Integrated Containers.

The Cloud Foundry Diego project integrates Docker into the Cloud Foundry PaaS.

The GearD project aims to integrate Docker into the Red Hat's OpenShift Origin PaaS.

The Apprenda PaaS integrates Docker containers in version 6.0 of its product.

History

Solomon Hykes started Docker in France as an internal project within dotCloud, a platform-as-a-service company, with initial contributions by other dotCloud engineers including Andrea Luzzardi and Francois-Xavier Bourlet. Jeff Lindsay also became involved as an independent collaborator. Docker represents an evolution of dotCloud's proprietary technology, which is itself built on earlier open-source projects such as Cloudlets.

Docker was released as open source in March 2013. On March 13, 2014, with the release of version 0.9, Docker dropped LXC as the default execution environment and replaced it with its own libcontainer library written in the Go programming language. As of October 24, 2015, the project had over 25,600 GitHub stars (making it the 20th most-starred GitHub project), over 6,800 forks, and nearly 1,100 contributors.

A May 2015 analysis showed the following organizations as main contributors to Docker: the Docker team, Red Hat, IBM, Google, Cisco Systems and Amadeus IT Group.

Collaboration

• On July 23, 2013, dotCloud, Inc., the commercial entity behind Docker, announced that former Gluster and Plaxo CEO Ben Golub had joined the company, citing Docker as the primary future focus of the company.
• On September 19, 2013, Red Hat and Docker announced a significant collaboration around Fedora, Red Hat Enterprise Linux, and OpenShift.
• On January 22, 2014, Docker announced that it had completed a $15 million Series B venture capital round, led by Greylock Partners.
• On July 23, 2014, Docker acquired Orchard, makers of Fig. Montana Mendy, a contributor of Fig thought the acquisition of Fig was a "brilliant" one.
• On September 16, 2014, Docker announced that it had completed a $40 M Series C round, led by Sequoia Capital.
• On October 15, 2014, Microsoft announced integration of the Docker engine into the next (2016) Windows Server release, and native support for the Docker client role in Windows.
• On December 4, 2014, IBM announced a strategic partnership with Docker that enables enterprises to more efficiently, quickly and cost-effectively build and run the next generation of applications in the IBM Cloud.
• On April 14, 2015, Docker announced it had closed a Series D round of funding of $95 million led by Insight Venture Partners.
• On June 22, 2015, Docker and several other companies announced that they are working on a new vendor and operating-system-independent standard for software containers.
• On January 21, 2016, Docker announced they have acquired Unikernel Systems. Unikernels are an additional kind of container that they may use “if they want to continue the specialization” of their code output, said Anil Madhavapeddy, the former CTO of Unikernel Systems, who is now with Docker.

See also

• DevOps
• Operating system-level virtualization
• Operating system-level virtualization implementations
• Service Component Architecture

External links

• Official website
• docker on GitHub
• Multi-tenancy using Docker
• Docker 101 Tutorial on YouTube
• libcontainer git repo on GitHub
• Linux Containers and the future cloud, by Rami Rosen