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Cleaned up long lines, switched graphic to Docker logo. General cleanup.
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@ -1,80 +1,129 @@
Docker: the Linux container engine Docker: the Linux container engine
================================== ==================================
Docker is an open-source engine which automates the deployment of applications as highly portable, self-sufficient containers. Docker is an open-source engine which automates the deployment of
applications as highly portable, self-sufficient containers.
Docker containers are both *hardware-agnostic* and *platform-agnostic*. This means that they can run anywhere, from your Docker containers are both *hardware-agnostic* and
laptop to the largest EC2 compute instance and everything in between - and they don't require that you use a particular *platform-agnostic*. This means that they can run anywhere, from your
language, framework or packaging system. That makes them great building blocks for deploying and scaling web apps, databases laptop to the largest EC2 compute instance and everything in between -
and backend services without depending on a particular stack or provider. 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. Docker is an open-source implementation of the deployment engine which
It benefits directly from the experience accumulated over several years of large-scale operation and support of hundreds of thousands powers [dotCloud](http://dotcloud.com), a popular
of applications and databases. 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/sources/concepts/images/lego_docker.jpg "Docker") ![Docker L](docs/sources/concepts/images/dockerlogo-h.png "Docker")
## Better than VMs ## Better than VMs
A common method for distributing applications and sandbox their execution is to use virtual machines, or VMs. Typical VM formats A common method for distributing applications and sandbox their
are VMWare's vmdk, Oracle Virtualbox's vdi, and Amazon EC2's ami. In theory these formats should allow every developer to execution is to use virtual machines, or VMs. Typical VM formats are
automatically package their application into a "machine" for easy distribution and deployment. In practice, that almost never VMWare's vmdk, Oracle Virtualbox's vdi, and Amazon EC2's ami. In
happens, for a few reasons: 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. * *Size*: VMs are very large which makes them impractical to store
* *Performance*: running VMs consumes significant CPU and memory, which makes them impractical in many scenarios, for example local development of multi-tier applications, and and transfer.
large-scale deployment of cpu and memory-intensive applications on large numbers of machines. * *Performance*: running VMs consumes significant CPU and memory,
* *Portability*: competing VM environments don't play well with each other. Although conversion tools do exist, they are limited and add even more overhead. which makes them impractical in many scenarios, for example local
* *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: development of multi-tier applications, and large-scale deployment
building, testing and running their software. For example, VMs offer no facilities for application versioning, monitoring, configuration, logging or service discovery. 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, By contrast, Docker relies on a different sandboxing method known as
containerization takes place at the kernel level. Most modern operating system kernels now support the primitives necessary *containerization*. Unlike traditional virtualization,
for containerization, including Linux with [openvz](http://openvz.org), [vserver](http://linux-vserver.org) and more recently [lxc](http://lxc.sourceforge.net), containerization takes place at the kernel level. Most modern
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). 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 Docker builds on top of these low-level primitives to offer developers
all 4 problems. Docker containers are small (and their transfer can be optimized with layers), they have basically zero memory and cpu overhead, a portable format and runtime environment that solves all 4
they are completely portable and are designed from the ground up with an application-centric design. 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! The best part: because ``docker`` operates at the OS level, it can
still be run inside a VM!
## Plays well with others ## Plays well with others
Docker does not require that you buy into a particular programming language, framework, packaging system or configuration language. 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 Is your application a Unix process? Does it use files, tcp
arguments as inputs and outputs? Then docker can run it. 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. Can your application's build be expressed as a sequence of such
commands? Then ``docker`` can build it.
## Escape dependency hell ## Escape dependency hell
A common problem for developers is the difficulty of managing all their application's dependencies in a simple and automated way. 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: 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, * *Cross-platform dependencies*. Modern applications often depend on
internal components developed for another project, etc. These dependencies live in different "worlds" and require different tools - these tools typically don't work a combination of system libraries and binaries, language-specific
well with each other, requiring awkward custom integrations. 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 - * Conflicting dependencies. Different applications may depend on
but they all handle them in different and incompatible ways, which again forces the developer to do extra work. 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, * Custom dependencies. A developer may need to prepare a custom
others can't - and all of them handle it differently. 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, Docker solves dependency hell by giving the developer a simple way to
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 express *all* their application's dependencies in one place, and
*replace* your favorite packaging systems. It simply orchestrates their use in a simple and repeatable way. How does it do that? With layers. 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 Docker defines a build as running a sequence of Unix commands, one
(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 after the other, in the same container. Build commands modify the
commands, the *order* in which the commands are executed expresses *dependencies*. 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: Here's a typical Docker build process:
```bash ```bash
from ubuntu:12.10 from ubuntu:12.10
@ -87,7 +136,8 @@ run curl -L https://github.com/shykes/helloflask/archive/master.tar.gz | tar -xz
run cd helloflask-master && pip install -r requirements.txt 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. 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.
Install instructions Install instructions
@ -103,8 +153,9 @@ curl get.docker.io | sudo sh -x
Binary installs Binary installs
---------------- ----------------
Docker supports the following binary installation methods. Docker supports the following binary installation methods. Note that
Note that some methods are community contributions and not yet officially supported. some methods are community contributions and not yet officially
supported.
* [Ubuntu 12.04 and 12.10 (officially supported)](http://docs.docker.io/en/latest/installation/ubuntulinux/) * [Ubuntu 12.04 and 12.10 (officially supported)](http://docs.docker.io/en/latest/installation/ubuntulinux/)
* [Arch Linux](http://docs.docker.io/en/latest/installation/archlinux/) * [Arch Linux](http://docs.docker.io/en/latest/installation/archlinux/)
@ -115,15 +166,15 @@ Note that some methods are community contributions and not yet officially suppor
Installing from source Installing from source
---------------------- ----------------------
1. Make sure you have a [Go language](http://golang.org/doc/install) compiler and [git](http://git-scm.com) installed. 1. Make sure you have a [Go language](http://golang.org/doc/install)
compiler and [git](http://git-scm.com) installed.
2. Checkout the source code 2. Checkout the source code
```bash ```bash
git clone http://github.com/dotcloud/docker git clone http://github.com/dotcloud/docker
``` ```
3. Build the docker binary 3. Build the ``docker`` binary
```bash ```bash
cd docker cd docker
@ -134,17 +185,20 @@ Installing from source
Usage examples Usage examples
============== ==============
First run the docker daemon First run the ``docker`` daemon
--------------------------- -------------------------------
All the examples assume your machine is running the docker daemon. To run the docker daemon in the background, simply type: All the examples assume your machine is running the ``docker``
daemon. To run the ``docker`` daemon in the background, simply type:
```bash ```bash
# On a production system you want this running in an init script # On a production system you want this running in an init script
sudo docker -d & sudo docker -d &
``` ```
Now you can run docker in client mode: all commands will be forwarded to the docker daemon, so the client can run from any account. Now you can run ``docker`` in client mode: all commands will be
forwarded to the ``docker`` daemon, so the client can run from any
account.
```bash ```bash
# Now you can run docker commands from any account. # Now you can run docker commands from any account.
@ -152,7 +206,7 @@ docker help
``` ```
Throwaway shell in a base ubuntu image Throwaway shell in a base Ubuntu image
-------------------------------------- --------------------------------------
```bash ```bash
@ -202,7 +256,8 @@ docker commit -m "Installed curl" $CONTAINER $USER/betterbase
docker push $USER/betterbase docker push $USER/betterbase
``` ```
A list of publicly available images is [available here](https://github.com/dotcloud/docker/wiki/Public-docker-images). A list of publicly available images is [available
here](https://github.com/dotcloud/docker/wiki/Public-docker-images).
Expose a service on a TCP port Expose a service on a TCP port
------------------------------ ------------------------------
@ -229,32 +284,40 @@ Under the hood
Under the hood, Docker is built on the following components: Under the hood, Docker is built on the following components:
* The
* 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; [cgroup](http://blog.dotcloud.com/kernel-secrets-from-the-paas-garage-part-24-c)
and
* [AUFS](http://aufs.sourceforge.net/aufs.html), a powerful union filesystem with copy-on-write capabilities; [namespacing](http://blog.dotcloud.com/under-the-hood-linux-kernels-on-dotcloud-part)
capabilities of the Linux kernel;
* [AUFS](http://aufs.sourceforge.net/aufs.html), a powerful union
filesystem with copy-on-write capabilities;
* The [Go](http://golang.org) programming language; * The [Go](http://golang.org) programming language;
* [lxc](http://lxc.sourceforge.net/), a set of convenience scripts to
* [lxc](http://lxc.sourceforge.net/), a set of convenience scripts to simplify the creation of linux containers. simplify the creation of Linux containers.
Contributing to Docker Contributing to Docker
====================== ======================
Want to hack on Docker? Awesome! There are instructions to get you started on the website: http://docs.docker.io/en/latest/contributing/contributing/ Want to hack on Docker? Awesome! There are instructions to get you
started on the website:
http://docs.docker.io/en/latest/contributing/contributing/
They are probably not perfect, please let us know if anything feels wrong or incomplete. They are probably not perfect, please let us know if anything feels
wrong or incomplete.
Note Note
---- ----
We also keep the documentation in this repository. The website documentation is generated using sphinx using these sources. We also keep the documentation in this repository. The website
Please find it under docs/sources/ and read more about it https://github.com/dotcloud/docker/tree/master/docs/README.md documentation is generated using Sphinx using these sources. Please
find it under docs/sources/ and read more about it
https://github.com/dotcloud/docker/tree/master/docs/README.md
Please feel free to fix / update the documentation and send us pull requests. More tutorials are also welcome. Please feel free to fix / update the documentation and send us pull
requests. More tutorials are also welcome.
Setting up a dev environment Setting up a dev environment
@ -289,42 +352,96 @@ Run the `go install` command (above) to recompile docker.
What is a Standard Container? What is a Standard Container?
============================= =============================
Docker defines a unit of software delivery called a Standard Container. The goal of a Standard Container is to encapsulate a software component and all its dependencies in Docker defines a unit of software delivery called a Standard
a format that is self-describing and portable, so that any compliant runtime can run it without extra dependencies, regardless of the underlying machine and the contents of the container. Container. The goal of a Standard Container is to encapsulate a
software component and all its dependencies in a format that is
self-describing and portable, so that any compliant runtime can run it
without extra dependencies, regardless of the underlying machine and
the contents of the container.
The spec for Standard Containers is currently a work in progress, but it is very straightforward. It mostly defines 1) an image format, 2) a set of standard operations, and 3) an execution environment. The spec for Standard Containers is currently a work in progress, but
it is very straightforward. It mostly defines 1) an image format, 2) a
set of standard operations, and 3) an execution environment.
A great analogy for this is the shipping container. Just like how Standard Containers are a fundamental unit of software delivery, shipping containers (http://bricks.argz.com/ins/7823-1/12) are a fundamental unit of physical delivery. A great analogy for this is the shipping container. Just like how
Standard Containers are a fundamental unit of software delivery,
shipping containers are a fundamental unit of physical delivery.
### 1. STANDARD OPERATIONS ### 1. STANDARD OPERATIONS
Just like shipping containers, Standard Containers define a set of STANDARD OPERATIONS. Shipping containers can be lifted, stacked, locked, loaded, unloaded and labelled. Similarly, standard containers can be started, stopped, copied, snapshotted, downloaded, uploaded and tagged. Just like shipping containers, Standard Containers define a set of
STANDARD OPERATIONS. Shipping containers can be lifted, stacked,
locked, loaded, unloaded and labelled. Similarly, Standard Containers
can be started, stopped, copied, snapshotted, downloaded, uploaded and
tagged.
### 2. CONTENT-AGNOSTIC ### 2. CONTENT-AGNOSTIC
Just like shipping containers, Standard Containers are CONTENT-AGNOSTIC: all standard operations have the same effect regardless of the contents. A shipping container will be stacked in exactly the same way whether it contains Vietnamese powder coffee or spare Maserati parts. Similarly, Standard Containers are started or uploaded in the same way whether they contain a postgres database, a php application with its dependencies and application server, or Java build artifacts. Just like shipping containers, Standard Containers are
CONTENT-AGNOSTIC: all standard operations have the same effect
regardless of the contents. A shipping container will be stacked in
exactly the same way whether it contains Vietnamese powder coffee or
spare Maserati parts. Similarly, Standard Containers are started or
uploaded in the same way whether they contain a postgres database, a
php application with its dependencies and application server, or Java
build artifacts.
### 3. INFRASTRUCTURE-AGNOSTIC ### 3. INFRASTRUCTURE-AGNOSTIC
Both types of containers are INFRASTRUCTURE-AGNOSTIC: they can be transported to thousands of facilities around the world, and manipulated by a wide variety of equipment. A shipping container can be packed in a factory in Ukraine, transported by truck to the nearest routing center, stacked onto a train, loaded into a German boat by an Australian-built crane, stored in a warehouse at a US facility, etc. Similarly, a standard container can be bundled on my laptop, uploaded to S3, downloaded, run and snapshotted by a build server at Equinix in Virginia, uploaded to 10 staging servers in a home-made Openstack cluster, then sent to 30 production instances across 3 EC2 regions. Both types of containers are INFRASTRUCTURE-AGNOSTIC: they can be
transported to thousands of facilities around the world, and
manipulated by a wide variety of equipment. A shipping container can
be packed in a factory in Ukraine, transported by truck to the nearest
routing center, stacked onto a train, loaded into a German boat by an
Australian-built crane, stored in a warehouse at a US facility,
etc. Similarly, a standard container can be bundled on my laptop,
uploaded to S3, downloaded, run and snapshotted by a build server at
Equinix in Virginia, uploaded to 10 staging servers in a home-made
Openstack cluster, then sent to 30 production instances across 3 EC2
regions.
### 4. DESIGNED FOR AUTOMATION ### 4. DESIGNED FOR AUTOMATION
Because they offer the same standard operations regardless of content and infrastructure, Standard Containers, just like their physical counterpart, are extremely well-suited for automation. In fact, you could say automation is their secret weapon. Because they offer the same standard operations regardless of content
and infrastructure, Standard Containers, just like their physical
counterparts, are extremely well-suited for automation. In fact, you
could say automation is their secret weapon.
Many things that once required time-consuming and error-prone human effort can now be programmed. Before shipping containers, a bag of powder coffee was hauled, dragged, dropped, rolled and stacked by 10 different people in 10 different locations by the time it reached its destination. 1 out of 50 disappeared. 1 out of 20 was damaged. The process was slow, inefficient and cost a fortune - and was entirely different depending on the facility and the type of goods. Many things that once required time-consuming and error-prone human
effort can now be programmed. Before shipping containers, a bag of
powder coffee was hauled, dragged, dropped, rolled and stacked by 10
different people in 10 different locations by the time it reached its
destination. 1 out of 50 disappeared. 1 out of 20 was damaged. The
process was slow, inefficient and cost a fortune - and was entirely
different depending on the facility and the type of goods.
Similarly, before Standard Containers, by the time a software component ran in production, it had been individually built, configured, bundled, documented, patched, vendored, templated, tweaked and instrumented by 10 different people on 10 different computers. Builds failed, libraries conflicted, mirrors crashed, post-it notes were lost, logs were misplaced, cluster updates were half-broken. The process was slow, inefficient and cost a fortune - and was entirely different depending on the language and infrastructure provider. Similarly, before Standard Containers, by the time a software
component ran in production, it had been individually built,
configured, bundled, documented, patched, vendored, templated, tweaked
and instrumented by 10 different people on 10 different
computers. Builds failed, libraries conflicted, mirrors crashed,
post-it notes were lost, logs were misplaced, cluster updates were
half-broken. The process was slow, inefficient and cost a fortune -
and was entirely different depending on the language and
infrastructure provider.
### 5. INDUSTRIAL-GRADE DELIVERY ### 5. INDUSTRIAL-GRADE DELIVERY
There are 17 million shipping containers in existence, packed with every physical good imaginable. Every single one of them can be loaded onto the same boats, by the same cranes, in the same facilities, and sent anywhere in the World with incredible efficiency. It is embarrassing to think that a 30 ton shipment of coffee can safely travel half-way across the World in *less time* than it takes a software team to deliver its code from one datacenter to another sitting 10 miles away. There are 17 million shipping containers in existence, packed with
every physical good imaginable. Every single one of them can be loaded
onto the same boats, by the same cranes, in the same facilities, and
sent anywhere in the World with incredible efficiency. It is
embarrassing to think that a 30 ton shipment of coffee can safely
travel half-way across the World in *less time* than it takes a
software team to deliver its code from one datacenter to another
sitting 10 miles away.
With Standard Containers we can put an end to that embarrassment, by making INDUSTRIAL-GRADE DELIVERY of software a reality. With Standard Containers we can put an end to that embarrassment, by
making INDUSTRIAL-GRADE DELIVERY of software a reality.
@ -374,8 +491,10 @@ Standard Container Specification
### Legal ### Legal
Transfers of Docker shall be in accordance with applicable export controls of any country and all other applicable Transfers of Docker shall be in accordance with applicable export
legal requirements. Docker shall not be distributed or downloaded to or in Cuba, Iran, North Korea, Sudan or Syria controls of any country and all other applicable legal requirements.
and shall not be distributed or downloaded to any person on the Denied Persons List administered by the U.S. Docker shall not be distributed or downloaded to or in Cuba, Iran,
North Korea, Sudan or Syria and shall not be distributed or downloaded
to any person on the Denied Persons List administered by the U.S.
Department of Commerce. Department of Commerce.