Docker is a set of products that uses operating system-level virtualization to deliver software in packages called containers. Docker automates the deployment of applications within lightweight containers, enabling them to run consistently across different computing environments.
The core software that runs and manages these containers is called Docker Engine. Docker was first released in 2013 and continues to be developed by Docker, Inc. The platform includes both free and paid tiers.
Contents
History
Solomon Hykes started the Docker project in France as an internal project within dotCloud, a platform-as-a-service company.
dotCloud Inc. was founded by Kamel Founadi, Hykes, and Sebastien Pahl during the Y Combinator Summer 2010 startup incubator group and launched in 2011, and renamed to Docker Inc in 2013.
Docker debuted to the public in Santa Clara at PyCon 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. In March 2026, the Communications of the ACM featured Docker as the cover article in a retrospective article of the past decade.
Adoption
September 19, 2013: Red Hat and Docker announced a collaboration around Fedora, Red Hat Enterprise Linux (RHEL), and OpenShift.
October 15, 2014: Microsoft announced the integration of the Docker engine into Windows Server, 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 (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 were working on a new vendor and operating-system-independent standard for software containers.
December 2015: Oracle Cloud added Docker container support after acquiring StackEngine, a Docker container startup.
March 2016: Docker for Mac and Windows betas released.
April 2016: Windocks, an independent software vendor 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, Google, Huawei, IBM, Microsoft, and Red Hat.
June 8, 2016: Microsoft announced that Docker could now be used natively on Windows 10.
January 2017: An analysis of LinkedIn profile mentions showed Docker presence grew by 160% in 2016.
Design
Containers are isolated from one another and bundle their own software, libraries 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, they use fewer resources than virtual machines.
Docker can package an application and its dependencies in a virtual container that can, in principle, run on any Linux, Windows, or macOS computer. This enables the application to run in a variety of locations, such as on-premises, in public (see decentralized computing, distributed computing, and cloud computing) or private cloud. When running 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 OverlayFS) to allow containers to run within a single Linux instance, avoiding the overhead of starting and maintaining virtual machines. Docker on macOS uses a Linux virtual machine 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.
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 libcontainer) to use virtualization facilities provided directly by the Linux kernel, in addition to using abstracted virtualization interfaces via libvirt, LXC and systemd-nspawn.
Docker implements a high-level API to provide lightweight containers that run processes in isolation.
Components
The Docker software as a service offering consists of three components:
Software
The Docker daemon, called dockerd, is a persistent process that manages Docker containers and handles container objects. The daemon listens for requests that are 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.
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.
A Dockerfile is a text file that commonly specifies several aspects of a Docker image: the Linux distribution, installation commands for the programming language runtime environment and application source code.
Licensing model
The Docker Engine is licensed under the Apache License 2.0. Docker Desktop distributes some components that are licensed under the GNU General Public License. Docker Desktop is not free for large enterprises.
The Dockerfile files can be licensed under an open-source license. The scope of such a license statement is only the Dockerfile and not the container image.