README.md - third_party/github.com/moby/moby - Git at Google

 Docker: the Linux container engine
 ==================================

 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 that they can run anywhere, from your laptop to the largest
 EC2 compute instance and everything in between - and they don't require
 that you 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 is an open-source implementation of the deployment engine which
 powers [dotCloud](http://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.

 ![Docker L](docs/theme/mkdocs/images/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](http://openvz.org),
 [vserver](http://linux-vserver.org) and more recently
 [lxc](http://lxc.sourceforge.net), Solaris with
 [zones](http://docs.oracle.com/cd/E26502_01/html/E29024/preface-1.html#scrolltoc)
 and FreeBSD with
 [Jails](http://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 4 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.

 The best part: because Docker operates at the OS level, it can still be
 run inside a VM!

 ## Plays well with others

 Docker does not require that you 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 dependency hell by giving the developer a simple way to
 express *all* their application's dependencies in one place, and
 streamline the process of assembling them. If this makes you think of
 [XKCD 927](http://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
 RUN apt-get install -q -y python python-pip curl
 RUN curl -L 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 on your local machine as well as servers - both
 bare metal and virtualized.  It is available as a binary on most modern
 Linux systems, or as a VM on Windows, Mac and other systems.

 We also offer an [interactive tutorial](http://www.docker.com/tryit/)
 for quickly learning the basics of using Docker.

 For up-to-date install instructions, see the [Docs](http://docs.docker.com).

 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](http://docs.docker.com/examples/) in the
 documentation.

 Under the hood
 --------------

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

 * The
   [cgroup](http://blog.dotcloud.com/kernel-secrets-from-the-paas-garage-part-24-c)
   and
   [namespacing](http://blog.dotcloud.com/under-the-hood-linux-kernels-on-dotcloud-part)
   capabilities of the Linux kernel;
 * The [Go](http://golang.org) programming language.

 Contributing to Docker
 ======================

 Want to hack on Docker? Awesome! There are instructions to get you
 started [here](CONTRIBUTING.md).

 They are probably not perfect, please let us know if anything feels
 wrong or incomplete.

 ### Legal

 *Brought to you courtesy of our legal counsel. For more context,
 please see the Notice document.*

 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 http://www.bis.doc.gov


 Licensing
 =========
 Docker is licensed under the Apache License, Version 2.0. See LICENSE for full license text.
	Docker: the Linux container engine
	==================================

	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 that they can run anywhere, from your laptop to the largest
	EC2 compute instance and everything in between - and they don't require
	that you 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 is an open-source implementation of the deployment engine which
	powers [dotCloud](http://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.

	![Docker L](docs/theme/mkdocs/images/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](http://openvz.org),
	[vserver](http://linux-vserver.org) and more recently
	[lxc](http://lxc.sourceforge.net), Solaris with
	[zones](http://docs.oracle.com/cd/E26502_01/html/E29024/preface-1.html#scrolltoc)
	and FreeBSD with
	[Jails](http://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 4 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.

	The best part: because Docker operates at the OS level, it can still be
	run inside a VM!

	## Plays well with others

	Docker does not require that you 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 dependency hell by giving the developer a simple way to
	express all their application's dependencies in one place, and
	streamline the process of assembling them. If this makes you think of
	[XKCD 927](http://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
	RUN apt-get install -q -y python python-pip curl
	RUN curl -L 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 on your local machine as well as servers - both
	bare metal and virtualized. It is available as a binary on most modern
	Linux systems, or as a VM on Windows, Mac and other systems.

	We also offer an [interactive tutorial](http://www.docker.com/tryit/)
	for quickly learning the basics of using Docker.

	For up-to-date install instructions, see the [Docs](http://docs.docker.com).

	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](http://docs.docker.com/examples/) in the
	documentation.

	Under the hood
	--------------

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

	* The
	[cgroup](http://blog.dotcloud.com/kernel-secrets-from-the-paas-garage-part-24-c)
	and
	[namespacing](http://blog.dotcloud.com/under-the-hood-linux-kernels-on-dotcloud-part)
	capabilities of the Linux kernel;
	* The [Go](http://golang.org) programming language.

	Contributing to Docker
	======================

	Want to hack on Docker? Awesome! There are instructions to get you
	started [here](CONTRIBUTING.md).

	They are probably not perfect, please let us know if anything feels
	wrong or incomplete.

	### Legal

	*Brought to you courtesy of our legal counsel. For more context,
	please see the Notice document.*

	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 http://www.bis.doc.gov


	Licensing
	=========
	Docker is licensed under the Apache License, Version 2.0. See LICENSE for full license text.