Docker: the container engine [![Release](https://img.shields.io/github/release/docker/docker.svg)](https://github.com/docker/docker/releases/latest)

 ============================

 Docker is an open source project to pack, ship and run any application

 as a lightweight container.

 Docker containers are both *hardware-agnostic* and *platform-agnostic*.

 This means they can run anywhere, from your laptop to the largest

 cloud compute instance and everything in between - and they don't require

 you to use a particular language, framework or packaging system. That

 makes them great building blocks for deploying and scaling web apps,

 databases, and backend services without depending on a particular stack

 or provider.

 Docker began as an open-source implementation of the deployment engine which

 powers [dotCloud](https://www.dotcloud.com), a popular Platform-as-a-Service.

 It benefits directly from the experience accumulated over several years
 of large-scale operation and support of hundreds of thousands of
 applications and databases.

 ![](docs/static_files/docker-logo-compressed.png "Docker")

 ## Security Disclosure
 

 Security is very important to us. If you have any issue regarding security, 

 please disclose the information responsibly by sending an email to 
 security@docker.com and not by creating a github issue.

 ## Better than VMs

 A common method for distributing applications and sandboxing their

 execution is to use virtual machines, or VMs. Typical VM formats are

 VMware's vmdk, Oracle VirtualBox's vdi, and Amazon EC2's ami. In theory

 these formats should allow every developer to automatically package
 their application into a "machine" for easy distribution and deployment.
 In practice, that almost never happens, for a few reasons:

 
   * *Size*: VMs are very large which makes them impractical to store
      and transfer.
   * *Performance*: running VMs consumes significant CPU and memory,
     which makes them impractical in many scenarios, for example local
     development of multi-tier applications, and large-scale deployment
     of cpu and memory-intensive applications on large numbers of
     machines.
   * *Portability*: competing VM environments don't play well with each
      other. Although conversion tools do exist, they are limited and
      add even more overhead.
   * *Hardware-centric*: VMs were designed with machine operators in
     mind, not software developers. As a result, they offer very
     limited tooling for what developers need most: building, testing
     and running their software. For example, VMs offer no facilities
     for application versioning, monitoring, configuration, logging or
     service discovery.
 
 By contrast, Docker relies on a different sandboxing method known as

 *containerization*. Unlike traditional virtualization, containerization
 takes place at the kernel level. Most modern operating system kernels
 now support the primitives necessary for containerization, including

 Linux with [openvz](https://openvz.org),

 [vserver](http://linux-vserver.org) and more recently

 [lxc](https://linuxcontainers.org/), Solaris with

 [zones](https://docs.oracle.com/cd/E26502_01/html/E29024/preface-1.html#scrolltoc),

 and FreeBSD with

 [Jails](https://www.freebsd.org/doc/handbook/jails.html).

 Docker builds on top of these low-level primitives to offer developers a

 portable format and runtime environment that solves all four problems.

 Docker containers are small (and their transfer can be optimized with
 layers), they have basically zero memory and cpu overhead, they are

 completely portable, and are designed from the ground up with an

 application-centric design.

 Perhaps best of all, because Docker operates at the OS level, it can still be

 run inside a VM!

 ## Plays well with others

 Docker does not require you to buy into a particular programming
 language, framework, packaging system, or configuration language.

 Is your application a Unix process? Does it use files, tcp connections,
 environment variables, standard Unix streams and command-line arguments
 as inputs and outputs? Then Docker can run it.

 Can your application's build be expressed as a sequence of such

 commands? Then Docker can build it.

 ## Escape dependency hell
 

 A common problem for developers is the difficulty of managing all
 their application's dependencies in a simple and automated way.

 
 This is usually difficult for several reasons:
 

   * *Cross-platform dependencies*. Modern applications often depend on
     a combination of system libraries and binaries, language-specific
     packages, framework-specific modules, internal components
     developed for another project, etc. These dependencies live in
     different "worlds" and require different tools - these tools
     typically don't work well with each other, requiring awkward
     custom integrations.
 

   * *Conflicting dependencies*. Different applications may depend on

     different versions of the same dependency. Packaging tools handle
     these situations with various degrees of ease - but they all
     handle them in different and incompatible ways, which again forces
     the developer to do extra work.

   * *Custom dependencies*. A developer may need to prepare a custom

     version of their application's dependency. Some packaging systems
     can handle custom versions of a dependency, others can't - and all
     of them handle it differently.

 Docker solves the problem of dependency hell by giving the developer a simple
 way to express *all* their application's dependencies in one place, while
 streamlining the process of assembling them. If this makes you think of

 [XKCD 927](https://xkcd.com/927/), don't worry. Docker doesn't

 *replace* your favorite packaging systems. It simply orchestrates
 their use in a simple and repeatable way. How does it do that? With
 layers.

 Docker defines a build as running a sequence of Unix commands, one
 after the other, in the same container. Build commands modify the
 contents of the container (usually by installing new files on the
 filesystem), the next command modifies it some more, etc. Since each
 build command inherits the result of the previous commands, the
 *order* in which the commands are executed expresses *dependencies*.

 Here's a typical Docker build process:

 
 ```bash

 FROM ubuntu:12.04

 RUN apt-get update && apt-get install -y python python-pip curl

 RUN curl -sSL https://github.com/shykes/helloflask/archive/master.tar.gz | tar -xzv

 RUN cd helloflask-master && pip install -r requirements.txt

 ```
 

 Note that Docker doesn't care *how* dependencies are built - as long
 as they can be built by running a Unix command in a container.

 Getting started
 ===============

 Docker can be installed either on your computer for building applications or
 on servers for running them. To get started, [check out the installation
 instructions in the
 documentation](https://docs.docker.com/engine/installation/).

 We also offer an [interactive tutorial](https://www.docker.com/tryit/)

 for quickly learning the basics of using Docker.

 Usage examples
 ==============

 Docker can be used to run short-lived commands, long-running daemons

 (app servers, databases, etc.), interactive shell sessions, etc.

 You can find a [list of real-world

 examples](https://docs.docker.com/engine/examples/) in the

 documentation.

 Under the hood
 --------------
 
 Under the hood, Docker is built on the following components:
 

 * The

   [cgroups](https://www.kernel.org/doc/Documentation/cgroup-v1/cgroups.txt)

   and

   [namespaces](http://man7.org/linux/man-pages/man7/namespaces.7.html)

   capabilities of the Linux kernel

 * The [Go](https://golang.org) programming language

 * The [Docker Image Specification](https://github.com/docker/docker/blob/master/image/spec/v1.md)

 * The [Libcontainer Specification](https://github.com/opencontainers/runc/blob/master/libcontainer/SPEC.md)

 Contributing to Docker [![GoDoc](https://godoc.org/github.com/docker/docker?status.svg)](https://godoc.org/github.com/docker/docker)

 ======================
 

 | **Master** (Linux) | **Experimental** (linux) | **Windows** | **FreeBSD** |
 |------------------|----------------------|---------|---------|
 | [![Jenkins Build Status](https://jenkins.dockerproject.org/view/Docker/job/Docker%20Master/badge/icon)](https://jenkins.dockerproject.org/view/Docker/job/Docker%20Master/) | [![Jenkins Build Status](https://jenkins.dockerproject.org/view/Docker/job/Docker%20Master%20%28experimental%29/badge/icon)](https://jenkins.dockerproject.org/view/Docker/job/Docker%20Master%20%28experimental%29/) | [![Build Status](http://jenkins.dockerproject.org/job/Docker%20Master%20(windows)/badge/icon)](http://jenkins.dockerproject.org/job/Docker%20Master%20(windows)/) | [![Build Status](http://jenkins.dockerproject.org/job/Docker%20Master%20(freebsd)/badge/icon)](http://jenkins.dockerproject.org/job/Docker%20Master%20(freebsd)/) |

 Want to hack on Docker? Awesome! We have [instructions to help you get

 started contributing code or documentation](https://docs.docker.com/opensource/project/who-written-for/).

 These instructions are probably not perfect, please let us know if anything

 feels wrong or incomplete. Better yet, submit a PR and improve them yourself.

 Getting the development builds
 ==============================
 

 Want to run Docker from a master build? You can download 

 master builds at [master.dockerproject.org](https://master.dockerproject.org). 

 They are updated with each commit merged into the master branch.
 

 Don't know how to use that super cool new feature in the master build? Check
 out the master docs at

 [docs.master.dockerproject.org](http://docs.master.dockerproject.org).

 How the project is run
 ======================
 
 Docker is a very, very active project. If you want to learn more about how it is run,

 or want to get more involved, the best place to start is [the project directory](https://github.com/docker/docker/tree/master/project).

 
 We are always open to suggestions on process improvements, and are always looking for more maintainers.
 

 ### Talking to other Docker users and contributors
 
 <table class="tg">
   <col width="45%">
   <col width="65%">
   <tr>
     <td>Internet&nbsp;Relay&nbsp;Chat&nbsp;(IRC)</td>
     <td>
       <p>

         IRC is a direct line to our most knowledgeable Docker users; we have

         both the  <code>#docker</code> and <code>#docker-dev</code> group on
         <strong>irc.freenode.net</strong>.
         IRC is a rich chat protocol but it can overwhelm new users. You can search
         <a href="https://botbot.me/freenode/docker/#" target="_blank">our chat archives</a>.
       </p>
       Read our <a href="https://docs.docker.com/project/get-help/#irc-quickstart" target="_blank">IRC quickstart guide</a> for an easy way to get started.
     </td>
   </tr>
   <tr>
     <td>Google Groups</td>
     <td>
       There are two groups.
       <a href="https://groups.google.com/forum/#!forum/docker-user" target="_blank">Docker-user</a>
       is for people using Docker containers.
       The <a href="https://groups.google.com/forum/#!forum/docker-dev" target="_blank">docker-dev</a>
       group is for contributors and other people contributing to the Docker
       project.

       You can join them without an google account by sending an email to e.g. "docker-user+subscribe@googlegroups.com".
       After receiving the join-request message, you can simply reply to that to confirm the subscribtion.

     </td>
   </tr>
   <tr>
     <td>Twitter</td>
     <td>
       You can follow <a href="https://twitter.com/docker/" target="_blank">Docker's Twitter feed</a>
       to get updates on our products. You can also tweet us questions or just
       share blogs or stories.
     </td>
   </tr>
   <tr>
     <td>Stack Overflow</td>
     <td>

       Stack Overflow has over 7000 Docker questions listed. We regularly

       monitor <a href="https://stackoverflow.com/search?tab=newest&q=docker" target="_blank">Docker questions</a>
       and so do many other knowledgeable Docker users.
     </td>
   </tr>
 </table>
 

 ### Legal
 

 *Brought to you courtesy of our legal counsel. For more context,

 please see the [NOTICE](https://github.com/docker/docker/blob/master/NOTICE) document in this repo.*

 Use and transfer of Docker may be subject to certain restrictions by the

 United States and other governments.
 

 It is your responsibility to ensure that your use and/or transfer does not

 violate applicable laws.

 For more information, please see https://www.bis.doc.gov

 
 
 Licensing
 =========

 Docker is licensed under the Apache License, Version 2.0. See
 [LICENSE](https://github.com/docker/docker/blob/master/LICENSE) for the full
 license text.

 Other Docker Related Projects
 =============================

 There are a number of projects under development that are based on Docker's

 core technology. These projects expand the tooling built around the

 Docker platform to broaden its application and utility.

 * [Docker Registry](https://github.com/docker/distribution): Registry 
 server for Docker (hosting/delivery of repositories and images)

 * [Docker Machine](https://github.com/docker/machine): Machine management 

 for a container-centric world

 * [Docker Swarm](https://github.com/docker/swarm): A Docker-native clustering 

 system

 * [Docker Compose](https://github.com/docker/compose) (formerly Fig): 
 Define and run multi-container apps

 * [Kitematic](https://github.com/docker/kitematic): The easiest way to use 

 Docker on Mac and Windows

 If you know of another project underway that should be listed here, please help 
 us keep this list up-to-date by submitting a PR.

 
 Awesome-Docker
 ==============
 You can find more projects, tools and articles related to Docker on the [awesome-docker list](https://github.com/veggiemonk/awesome-docker). Add your project there.