Docker is a set of

platform as a service Platform as a service (PaaS) or application platform as a service (aPaaS) or platform-based service is a category of cloud computing services that allows customers to provision, instantiate, run, and manage a modular bundle comprising a computing ...

(PaaS) products that use

OS-level virtualization OS-level virtualization is an operating system (OS) paradigm in which the kernel allows the existence of multiple isolated user space instances, called ''containers'' (LXC, Solaris containers, Docker, Podman), ''zones'' (Solaris containers), '' ...

to deliver software in packages called ''

containers A container is any receptacle or enclosure for holding a product used in storage, packaging, and transportation, including shipping. Things kept inside of a container are protected on several sides by being inside of its structure. The term ...

''. The service has both free and premium tiers. The software that hosts the containers is called Docker Engine. It was first started in 2013 and is developed by

Docker, Inc. Docker, Inc. is an American technology company that develops productivity tools built around Docker, which automates the deployment of code inside software containers. Major products of the company are Docker Hub, a central repository of contain ...

Background

Containers are isolated from one another and bundle their own software,

libraries A library is a collection of Document, materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or electronic media, digital access (soft copies) materials, and may be a ...

and configuration files; they can communicate with each other through well-defined channels. Because all of the containers share the services of a single

operating system kernel The kernel is a computer program at the core of a computer's operating system and generally has complete control over everything in the system. It is the portion of the operating system code that is always resident in memory and facilitates in ...

, they use fewer resources than

virtual machine In computing, a virtual machine (VM) is the virtualization/ emulation of a computer system. Virtual machines are based on computer architectures and provide functionality of a physical computer. Their implementations may involve specialized h ...

Operation

Docker can package an application and its dependencies in a virtual container that can run on any Linux, Windows, or macOS computer. This enables the application to run in a variety of locations, such as

on-premises On-premises software (abbreviated to on-prem, and incorrectly referred to as on-premise) is installed and runs on computers on the premises of the person or organization using the software, rather than at a remote facility such as a server farm ...

, in

public In public relations and communication science, publics are groups of individual people, and the public (a.k.a. the general public) is the totality of such groupings. This is a different concept to the sociological concept of the ''Öffentlichk ...

(see

decentralized computing Decentralized computing is the allocation of resources, both hardware and software, to each individual workstation, or office location. In contrast, centralized computing exists when the majority of functions are carried out, or obtained from a ...

distributed computing A distributed system is a system whose components are located on different networked computers, which communicate and coordinate their actions by passing messages to one another from any system. Distributed computing is a field of computer sci ...

, and

cloud computing Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mu ...

) or

private cloud Cloud computing is the on-demand availability of computer system resources, especially data storage ( cloud storage) and computing power, without direct active management by the user. Large clouds often have functions distributed over mul ...

. When running on Linux, Docker uses the resource isolation features of the Linux kernel (such as

cgroups cgroups (abbreviated from control groups) is a Linux kernel feature that limits, accounts for, and isolates the resource usage (CPU, memory, disk I/O, network, etc.) of a collection of processes. Engineers at Google started the work on this ...

and kernel

namespaces In computing, a namespace is a set of signs (''names'') that are used to identify and refer to objects of various kinds. A namespace ensures that all of a given set of objects have unique names so that they can be easily identified. Namespaces ...

) and a union-capable file system (such as

OverlayFS In computing, OverlayFS is a union mount filesystem implementation for Linux. It combines multiple different underlying mount points into one, resulting in single directory structure that contains underlying files and sub-directories from all sou ...

) to allow containers to run within a single Linux instance, avoiding the overhead of starting and maintaining

s. Docker on

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

uses a Linux

to run the containers. Because Docker containers are lightweight, a single server or virtual machine can run several containers simultaneously. A 2018 analysis found that a typical Docker use case involves running eight containers per host, and that a quarter of analyzed organizations run 18 or more per host. It can also be installed on a single board computer like the

Raspberry Pi Raspberry Pi () is a series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in association with Broadcom. The Raspberry Pi project originally leaned towards the promotion of teaching basic ...

. 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 for memory and CPU. Since version 0.9, Docker includes its own component (called "") to use virtualization facilities provided directly by the Linux kernel, in addition to using abstracted virtualization interfaces via

libvirt libvirt is an open-source API, daemon and management tool for managing platform virtualization. It can be used to manage KVM, Xen, VMware ESXi, QEMU and other virtualization technologies. These APIs are widely used in the orchestration laye ...

, LXC and systemd-nspawn. Docker implements a high-level

API An application programming interface (API) is a way for two or more computer programs to communicate with each other. It is a type of software interface, offering a service to other pieces of software. A document or standard that describes how ...

to provide lightweight containers that run processes in isolation. Docker containers are standard processes, so it is possible to use kernel features to monitor their execution—including for example the use of tools like strace to observe and intercede with system calls.

Components

The Docker software as a service offering consists of three components: * Software: The Docker

daemon Daimon or Daemon (Ancient Greek: , "god", "godlike", "power", "fate") originally referred to a lesser deity or guiding spirit such as the daimons of ancient Greek religion and Greek mythology, mythology and of later Hellenistic religion and Hell ...

, called dockerd, is a persistent process that manages Docker containers and handles container objects. The daemon listens for requests sent via the Docker Engine API. The Docker client program, called docker, provides a command-line interface (CLI), that allows users to interact with Docker daemons. * Objects: Docker objects are various entities used to assemble an application in Docker. The main classes of Docker objects are images, containers, and services. ** A Docker container is a standardized, encapsulated environment that runs applications. A container is managed using the Docker API or

CLI CLI may refer to: Computing * Call Level Interface, an SQL database management API * Command-line interface, of a computer program * Command-line interpreter or command language interpreter; see List of command-line interpreters * CLI (x86 instruc ...

. ** A Docker image is a read-only template used to build containers. Images are used to store and ship applications. ** A Docker service allows containers to be scaled across multiple Docker daemons. The result is known as a ''swarm'', a set of cooperating daemons that communicate through the Docker API. * Registries: A Docker registry is a repository for Docker images. Docker clients connect to registries to download ("pull") images for use or upload ("push") images that they have built. Registries can be public or private. The main public registry is Docker Hub. Docker Hub is the default registry where Docker looks for images. Docker registries also allow the creation of notifications based on events.

Tools

* Docker Compose is a tool for defining and running multi-container Docker applications. It uses

YAML YAML ( and ) (''see '') is a human-readable data-serialization language. It is commonly used for configuration files and in applications where data is being stored or transmitted. YAML targets many of the same communications applications as Ext ...

files to configure the application's services and performs the creation and start-up process of all the containers with a single command. The docker''-compose'' CLI utility allows users to run commands on multiple containers at once, for example, building images,

scaling Scaling may refer to: Science and technology Mathematics and physics * Scaling (geometry), a linear transformation that enlarges or diminishes objects * Scale invariance, a feature of objects or laws that do not change if scales of length, energ ...

containers, running containers that were stopped, and more. Commands related to image manipulation, or user-interactive options, are not relevant in Docker Compose because they address one container. The docker-compose.yml file is used to define an application's services and includes various configuration options. For example, the build option defines configuration options such as the Dockerfile path, the command option allows one to override default Docker commands, and more. The first public beta version of Docker Compose (version 0.0.1) was released on December 21, 2013. The first production-ready version (1.0) was made available on October 16, 2014. * Docker Swarm provides native clustering functionality for Docker containers, which turns a group of Docker engines into a single virtual Docker engine. In Docker 1.12 and higher, Swarm mode is integrated with Docker Engine. The docker swarm CLI utility allows users to run Swarm containers, create discovery tokens, list nodes in the cluster, and more. The docker node CLI utility allows users to run various commands to manage nodes in a swarm, for example, listing the nodes in a swarm, updating nodes, and removing nodes from the swarm. Docker manages swarms using the

Raft A raft is any flat structure for support or transportation over water. It is usually of basic design, characterized by the absence of a hull. Rafts are usually kept afloat by using any combination of buoyant materials such as wood, sealed barrels ...

consensus algorithm. According to Raft, for an update to be performed, the majority of Swarm nodes need to agree on the update. * Docker Volume facilitates the independent persistence of data, allowing data to remain even after the container is deleted or re-created.

History

Docker Inc. was founded by Kamel Founadi, Solomon Hykes, and Sebastien Pahl during the

Y Combinator Y Combinator (YC) is an American technology startup accelerator launched in March 2005. It has been used to launch more than 3,000 companies, including Airbnb, Coinbase, Cruise, DoorDash, Dropbox, Instacart, Quora, PagerDuty, Reddit, St ...

Summer 2010 startup incubator group and launched in 2011. The startup was also one of the 12 startups in ''Founder's Den'' first cohort. Hykes started the Docker project in France as an internal project within dotCloud, a

platform-as-a-service Platform as a service (PaaS) or application platform as a service (aPaaS) or platform-based service is a category of cloud computing services that allows customers to provision, instantiate, run, and manage a modular bundle comprising a computin ...

company. Docker debuted to the public in Santa Clara at

PyCon The Python Conference (also called PyCon) is the largestpage 10 annual convention for the discussion and promotion of the Python programming language. It originated in the United States but is also held in more than 40 other countries. It was one ...

in 2013. It was released as open-source in March 2013. At the time, it used LXC as its default execution environment. One year later, with the release of version 0.9, Docker replaced LXC with its own component, ''libcontainer'', which was written in the Go programming language. In 2017, Docker created the Moby project for open research and development.

Adoption

* September 19, 2013: Red Hat and Docker announced a collaboration around Fedora,

Red Hat Enterprise Linux Red Hat Enterprise Linux (RHEL) is a commercial open-source Linux distribution developed by Red Hat for the commercial market. Red Hat Enterprise Linux is released in server versions for x86-64, Power ISA, ARM64, and IBM Z and a desktop ...

(RHEL), and

OpenShift 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 Kuber ...

. * October 15, 2014:

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washin ...

announced the integration of the Docker engine into

Windows Server Windows Server (formerly Windows NT Server) is a group of operating systems (OS) for servers that Microsoft has been developing since July 27, 1993. The first OS that was released for this platform was Windows NT 3.1 Advanced Server. With the r ...

, as well as native support for the Docker client role in Windows. * November 2014: Docker container services were announced for the

Amazon Elastic Compute Cloud Amazon Elastic Compute Cloud (EC2) is a part of Amazon.com's cloud-computing platform, Amazon Web Services (AWS), that allows users to rent virtual computers on which to run their own computer applications. EC2 encourages scalable deployment o ...

(EC2). * November 10, 2014: Docker announced a partnership with Stratoscale. * December 4, 2014: IBM announced a strategic partnership with Docker that enables Docker to integrate more closely with the IBM Cloud. * 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. * December 2015:

Oracle Cloud Oracle Cloud is a cloud computing service offered by Oracle Corporation providing servers, storage, network, applications and services through a global network of Oracle Corporation managed data centers. The company allows ...

added Docker container support after acquiring StackEngine, a Docker container startup. * April 2016: Windocks, an independent ISV released a port of Docker's open source project to Windows, supporting Windows Server 2012 R2 and Server 2016, with all editions of SQL Server 2008 onward. * May 2016: analysis showed the following organizations as main contributors to Docker: The Docker team,

Cisco Cisco Systems, Inc., commonly known as Cisco, is an American-based multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, ...

Google Google LLC () is an American Multinational corporation, multinational technology company focusing on Search Engine, search engine technology, online advertising, cloud computing, software, computer software, quantum computing, e-commerce, ar ...

Huawei Huawei Technologies Co., Ltd. ( ; ) is a Chinese multinational technology corporation headquartered in Shenzhen, Guangdong, China. It designs, develops, produces and sells telecommunications equipment, consumer electronics and various smar ...

, IBM,

, and Red Hat. * June 8, 2016: Microsoft announced that Docker could now be used natively on

Windows 10 Windows 10 is a major release of Microsoft's Windows NT operating system. It is the direct successor to Windows 8.1, which was released nearly two years earlier. It was released to manufacturing on July 15, 2015, and later to retail on J ...

. * January 2017: An analysis of

LinkedIn LinkedIn () is an American business and employment-oriented online service that operates via websites and mobile apps. Launched on May 5, 2003, the platform is primarily used for professional networking and career development, and allows job se ...

profile mentions showed Docker presence grew by 160% in 2016. * May 6, 2019: Microsoft announced the second version of

Windows Subsystem for Linux Windows is a group of several proprietary graphical operating system families developed and marketed by Microsoft. Each family caters to a certain sector of the computing industry. For example, Windows NT for consumers, Windows Server for ser ...

(WSL). Docker, Inc. announced that it has started working on a version of Docker for Windows that runs on WSL 2. In particular, this means Docker can run on Windows 10 Home (previously it was limited to Windows Pro and Enterprise since it used Hyper-V). * August 2020: Microsoft announced backport of WSL2 to Windows 10 versions 1903 and 1909 (previously WSL2 was available only on version 2004) and Docker developers announced availability of Docker for these platforms. *August 2021: Docker Desktop for Windows and MacOS is no longer free for enterprise users. Docker ended free Docker Desktop use for larger business customers and replaced its Free plan with a Personal plan. Docker on Linux distros remains unaffected.

References

External links

*
Container Terminology - ''Practical terminology''
{{Linux containers 2013 software Containerization software Free software programmed in Go Free software Free virtualization software Linux containerization Operating system security Operating system technology Virtualization software for Linux