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Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
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9 KiB
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220 lines
9 KiB
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:title: FAQ
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:description: Most frequently asked questions.
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:keywords: faq, questions, documentation, docker
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FAQ
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===
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Most frequently asked questions.
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--------------------------------
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How much does Docker cost?
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..........................
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Docker is 100% free, it is open source, so you can use it without paying.
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What open source license are you using?
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.......................................
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We are using the Apache License Version 2.0, see it here:
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https://github.com/dotcloud/docker/blob/master/LICENSE
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Does Docker run on Mac OS X or Windows?
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.......................................
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Not at this time, Docker currently only runs on Linux, but you can
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use VirtualBox to run Docker in a virtual machine on your box, and
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get the best of both worlds. Check out the
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:ref:`macosx` and :ref:`windows` installation
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guides.
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How do containers compare to virtual machines?
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..............................................
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They are complementary. VMs are best used to allocate chunks of
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hardware resources. Containers operate at the process level, which
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makes them very lightweight and perfect as a unit of software
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delivery.
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What does Docker add to just plain LXC?
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.......................................
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Docker is not a replacement for LXC. "LXC" refers to capabilities
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of the Linux kernel (specifically namespaces and control groups)
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which allow sandboxing processes from one another, and controlling
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their resource allocations. On top of this low-level foundation of
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kernel features, Docker offers a high-level tool with several
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powerful functionalities:
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* *Portable deployment across machines.*
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Docker defines a format for bundling an application and all its
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dependencies into a single object which can be transferred to
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any Docker-enabled machine, and executed there with the
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guarantee that the execution environment exposed to the
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application will be the same. LXC implements process sandboxing,
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which is an important pre-requisite for portable deployment, but
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that alone is not enough for portable deployment. If you sent me
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a copy of your application installed in a custom LXC
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configuration, it would almost certainly not run on my machine
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the way it does on yours, because it is tied to your machine's
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specific configuration: networking, storage, logging, distro,
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etc. Docker defines an abstraction for these machine-specific
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settings, so that the exact same Docker container can run -
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unchanged - on many different machines, with many different
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configurations.
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* *Application-centric.*
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Docker is optimized for the deployment of applications, as
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opposed to machines. This is reflected in its API, user
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interface, design philosophy and documentation. By contrast, the
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``lxc`` helper scripts focus on containers as lightweight
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machines - basically servers that boot faster and need less
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RAM. We think there's more to containers than just that.
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* *Automatic build.*
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Docker includes :ref:`a tool for developers to automatically
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assemble a container from their source code <dockerbuilder>`,
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with full control over application dependencies, build tools,
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packaging etc. They are free to use ``make, maven, chef, puppet,
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salt,`` Debian packages, RPMs, source tarballs, or any
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combination of the above, regardless of the configuration of the
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machines.
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* *Versioning.*
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Docker includes git-like capabilities for tracking successive
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versions of a container, inspecting the diff between versions,
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committing new versions, rolling back etc. The history also
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includes how a container was assembled and by whom, so you get
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full traceability from the production server all the way back to
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the upstream developer. Docker also implements incremental
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uploads and downloads, similar to ``git pull``, so new versions
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of a container can be transferred by only sending diffs.
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* *Component re-use.*
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Any container can be used as a :ref:`"base image"
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<base_image_def>` to create more specialized components. This
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can be done manually or as part of an automated build. For
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example you can prepare the ideal Python environment, and use it
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as a base for 10 different applications. Your ideal Postgresql
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setup can be re-used for all your future projects. And so on.
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* *Sharing.*
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Docker has access to a `public registry
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<http://index.docker.io>`_ where thousands of people have
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uploaded useful containers: anything from Redis, CouchDB,
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Postgres to IRC bouncers to Rails app servers to Hadoop to base
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images for various Linux distros. The :ref:`registry
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<registryindexspec>` also includes an official "standard
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library" of useful containers maintained by the Docker team. The
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registry itself is open-source, so anyone can deploy their own
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registry to store and transfer private containers, for internal
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server deployments for example.
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* *Tool ecosystem.*
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Docker defines an API for automating and customizing the
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creation and deployment of containers. There are a huge number
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of tools integrating with Docker to extend its
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capabilities. PaaS-like deployment (Dokku, Deis, Flynn),
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multi-node orchestration (Maestro, Salt, Mesos, Openstack Nova),
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management dashboards (docker-ui, Openstack Horizon, Shipyard),
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configuration management (Chef, Puppet), continuous integration
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(Jenkins, Strider, Travis), etc. Docker is rapidly establishing
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itself as the standard for container-based tooling.
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What is different between a Docker container and a VM?
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......................................................
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There's a great StackOverflow answer `showing the differences <http://stackoverflow.com/questions/16047306/how-is-docker-io-different-from-a-normal-virtual-machine>`_.
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Do I lose my data when the container exits?
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...........................................
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Not at all! Any data that your application writes to disk gets preserved
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in its container until you explicitly delete the container. The file
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system for the container persists even after the container halts.
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How far do Docker containers scale?
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Some of the largest server farms in the world today are based on containers.
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Large web deployments like Google and Twitter, and platform providers such as
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Heroku and dotCloud all run on container technology, at a scale of hundreds of
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thousands or even millions of containers running in parallel.
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How do I connect Docker containers?
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Currently the recommended way to link containers is via the `link` primitive.
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You can see details of how to `work with links here
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<http://docs.docker.io/en/latest/use/working_with_links_names/>`_.
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Also of useful when enabling more flexible service portability is the
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`Ambassador linking pattern
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<http://docs.docker.io/en/latest/use/ambassador_pattern_linking/>`_.
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How do I run more than one process in a Docker container?
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.........................................................
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Any capable process supervisor such as http://supervisord.org/, runit, s6, or
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daemontools can do the trick. Docker will start up the process management
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daemon which will then fork to run additional processes. As long as the
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processor manager daemon continues to run, the container will continue to as
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well. You can see a more substantial example `that uses supervisord here
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<http://docs.docker.io/en/latest/examples/using_supervisord/>`_.
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What platforms does Docker run on?
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Linux:
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- Ubuntu 12.04, 13.04 et al
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- Fedora 19/20+
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- RHEL 6.5+
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- Centos 6+
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- Gentoo
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- ArchLinux
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- openSUSE 12.3+
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- CRUX 3.0+
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Cloud:
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- Amazon EC2
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- Google Compute Engine
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- Rackspace
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How do I report a security issue with Docker?
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You can learn about the project's security policy `here <http://www.docker.io/security/>`_
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and report security issues to this `mailbox <mailto:security@docker.com>`_.
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Can I help by adding some questions and answers?
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................................................
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Definitely! You can fork `the repo`_ and edit the documentation sources.
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Where can I find more answers?
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..............................
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You can find more answers on:
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* `Docker user mailinglist`_
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* `Docker developer mailinglist`_
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* `IRC, docker on freenode`_
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* `GitHub`_
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* `Ask questions on Stackoverflow`_
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* `Join the conversation on Twitter`_
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.. _Docker user mailinglist: https://groups.google.com/d/forum/docker-user
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.. _Docker developer mailinglist: https://groups.google.com/d/forum/docker-dev
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.. _the repo: http://www.github.com/dotcloud/docker
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.. _IRC, docker on freenode: irc://chat.freenode.net#docker
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.. _Github: http://www.github.com/dotcloud/docker
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.. _Ask questions on Stackoverflow: http://stackoverflow.com/search?q=docker
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.. _Join the conversation on Twitter: http://twitter.com/docker
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Looking for something else to read? Checkout the :ref:`hello_world` example.
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