README
¶
Docker: the 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 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, 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.
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, vserver and more recently lxc, Solaris with zones, and FreeBSD with Jails.
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:
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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.
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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.
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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, 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:
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.
We also offer an interactive tutorial 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 in the documentation.
Under the hood
Under the hood, Docker is built on the following components:
- The cgroups and namespaces capabilities of the Linux kernel
- The Go programming language
- The Docker Image Specification
- The Libcontainer Specification
Contributing to Docker 
| Master (Linux) | Experimental (linux) | Windows | FreeBSD |
|---|---|---|---|
Want to hack on Docker? Awesome! We have instructions to help you get started contributing code or documentation.
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. 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.
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.
We are always open to suggestions on process improvements, and are always looking for more maintainers.
Talking to other Docker users and contributors
| Internet Relay Chat (IRC) |
IRC a direct line to our most knowledgeable Docker users; we have
both the |
| Google Groups | There are two groups. Docker-user is for people using Docker containers. The docker-dev group is for contributors and other people contributing to the Docker project. |
| You can follow Docker's Twitter feed to get updates on our products. You can also tweet us questions or just share blogs or stories. | |
| Stack Overflow | Stack Overflow has over 7000 Docker questions listed. We regularly monitor Docker questions and so do many other knowledgeable Docker users. |
Legal
Brought to you courtesy of our legal counsel. For more context, please see the 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 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: Registry server for Docker (hosting/delivery of repositories and images)
- Docker Machine: Machine management for a container-centric world
- Docker Swarm: A Docker-native clustering system
- Docker Compose (formerly Fig): Define and run multi-container apps
- 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. Add your project there.
Directories
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| Path | Synopsis |
|---|---|
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client
Package client provides a command-line interface for Docker.
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Package client provides a command-line interface for Docker. |
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Package builder defines interfaces for any Docker builder to implement.
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Package builder defines interfaces for any Docker builder to implement. |
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dockerfile
Package dockerfile is the evaluation step in the Dockerfile parse/evaluate pipeline.
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Package dockerfile is the evaluation step in the Dockerfile parse/evaluate pipeline. |
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dockerfile/command
Package command contains the set of Dockerfile commands.
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Package command contains the set of Dockerfile commands. |
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dockerfile/parser
Package parser implements a parser and parse tree dumper for Dockerfiles.
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Package parser implements a parser and parse tree dumper for Dockerfiles. |
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contrib
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Package daemon exposes the functions that occur on the host server that the Docker daemon is running.
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Package daemon exposes the functions that occur on the host server that the Docker daemon is running. |
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logger
Package logger defines interfaces that logger drivers implement to log messages.
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Package logger defines interfaces that logger drivers implement to log messages. |
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logger/awslogs
Package awslogs provides the logdriver for forwarding container logs to Amazon CloudWatch Logs
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Package awslogs provides the logdriver for forwarding container logs to Amazon CloudWatch Logs |
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logger/fluentd
Package fluentd provides the log driver for forwarding server logs to fluentd endpoints.
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Package fluentd provides the log driver for forwarding server logs to fluentd endpoints. |
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logger/gelf
Package gelf provides the log driver for forwarding server logs to endpoints that support the Graylog Extended Log Format.
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Package gelf provides the log driver for forwarding server logs to endpoints that support the Graylog Extended Log Format. |
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logger/journald
Package journald provides the log driver for forwarding server logs to endpoints that receive the systemd format.
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Package journald provides the log driver for forwarding server logs to endpoints that receive the systemd format. |
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logger/jsonfilelog
Package jsonfilelog provides the default Logger implementation for Docker logging.
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Package jsonfilelog provides the default Logger implementation for Docker logging. |
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logger/splunk
Package splunk provides the log driver for forwarding server logs to Splunk HTTP Event Collector endpoint.
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Package splunk provides the log driver for forwarding server logs to Splunk HTTP Event Collector endpoint. |
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logger/syslog
Package syslog provides the logdriver for forwarding server logs to syslog endpoints.
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Package syslog provides the logdriver for forwarding server logs to syslog endpoints. |
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Package dockerversion is auto-generated at build-time
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Package dockerversion is auto-generated at build-time |
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Package layer is package for managing read only and read-write mounts on the union file system driver.
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Package layer is package for managing read only and read-write mounts on the union file system driver. |
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migrate
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pkg
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filenotify
Package filenotify provides a mechanism for watching file(s) for changes.
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Package filenotify provides a mechanism for watching file(s) for changes. |
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integration/checker
Package checker provide Docker specific implementations of the go-check.Checker interface.
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Package checker provide Docker specific implementations of the go-check.Checker interface. |
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jsonlog
Package jsonlog provides helper functions to parse and print time (time.Time) as JSON.
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Package jsonlog provides helper functions to parse and print time (time.Time) as JSON. |
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locker
Package locker provides a mechanism for creating finer-grained locking to help free up more global locks to handle other tasks.
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Package locker provides a mechanism for creating finer-grained locking to help free up more global locks to handle other tasks. |
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parsers
Package parsers provides helper functions to parse and validate different type of string.
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Package parsers provides helper functions to parse and validate different type of string. |
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parsers/kernel
Package kernel provides helper function to get, parse and compare kernel versions for different platforms.
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Package kernel provides helper function to get, parse and compare kernel versions for different platforms. |
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parsers/operatingsystem
Package operatingsystem provides helper function to get the operating system name for different platforms.
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Package operatingsystem provides helper function to get the operating system name for different platforms. |
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pidfile
Package pidfile provides structure and helper functions to create and remove PID file.
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Package pidfile provides structure and helper functions to create and remove PID file. |
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platform
Package platform provides helper function to get the runtime architecture for different platforms.
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Package platform provides helper function to get the runtime architecture for different platforms. |
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plugins
Package plugins provides structures and helper functions to manage Docker plugins.
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Package plugins provides structures and helper functions to manage Docker plugins. |
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pools
Package pools provides a collection of pools which provide various data types with buffers.
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Package pools provides a collection of pools which provide various data types with buffers. |
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proxy
Package proxy provides a network Proxy interface and implementations for TCP and UDP.
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Package proxy provides a network Proxy interface and implementations for TCP and UDP. |
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registrar
Package registrar provides name registration.
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Package registrar provides name registration. |
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signal
Package signal provides helper functions for dealing with signals across various operating systems.
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Package signal provides helper functions for dealing with signals across various operating systems. |
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streamformatter
Package streamformatter provides helper functions to format a stream.
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Package streamformatter provides helper functions to format a stream. |
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stringid
Package stringid provides helper functions for dealing with string identifiers
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Package stringid provides helper functions for dealing with string identifiers |
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stringutils
Package stringutils provides helper functions for dealing with strings.
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Package stringutils provides helper functions for dealing with strings. |
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tailfile
Package tailfile provides helper functions to read the nth lines of any ReadSeeker.
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Package tailfile provides helper functions to read the nth lines of any ReadSeeker. |
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tarsum
Package tarsum provides algorithms to perform checksum calculation on filesystem layers.
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Package tarsum provides algorithms to perform checksum calculation on filesystem layers. |
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term
Package term provides provides structures and helper functions to work with terminal (state, sizes).
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Package term provides provides structures and helper functions to work with terminal (state, sizes). |
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tlsconfig
Package tlsconfig provides primitives to retrieve secure-enough TLS configurations for both clients and servers.
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Package tlsconfig provides primitives to retrieve secure-enough TLS configurations for both clients and servers. |
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truncindex
Package truncindex provides a general 'index tree', used by Docker in order to be able to reference containers by only a few unambiguous characters of their id.
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Package truncindex provides a general 'index tree', used by Docker in order to be able to reference containers by only a few unambiguous characters of their id. |
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urlutil
Package urlutil provides helper function to check urls kind.
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Package urlutil provides helper function to check urls kind. |
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useragent
Package useragent provides helper functions to pack version information into a single User-Agent header.
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Package useragent provides helper functions to pack version information into a single User-Agent header. |
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Package registry contains client primitives to interact with a remote Docker registry.
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Package registry contains client primitives to interact with a remote Docker registry. |
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local
Package local provides the default implementation for volumes.
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Package local provides the default implementation for volumes. |