mirror of https://github.com/docker/docs.git
simplify FAQ (#4447)
* simplify FAQ * address feedback * fixed links, copyedits for line length Signed-off-by: Victoria Bialas <victoria.bialas@docker.com>
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Michael Friis
Victoria Bialas
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119
engine/faq.md
119
engine/faq.md
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@ -3,54 +3,14 @@ description: Most frequently asked questions.
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keywords: faq, questions, documentation, docker
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redirect_from:
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- /engine/misc/faq/
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title: Docker Engine frequently asked questions (FAQ)
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title: Docker frequently asked questions (FAQ)
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---
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If you don't see your question here, feel free to submit new ones to
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<docs@docker.com>. Or, you can fork [the
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repo](https://github.com/moby/moby) and contribute them yourself by editing
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the documentation sources.
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### Does Docker run on Linux, macOS, and Windows?
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You can run both Linux and Windows programs and excutables in Docker containers. The Docker platform runs natively on Linux (on x84-64, ARM and many other CPU architectures) and on Windows (x86-64).
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### How much does Engine cost?
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Docker Engine 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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We are using the Apache License Version 2.0, see it here:
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[https://github.com/moby/moby/blob/master/LICENSE](
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https://github.com/moby/moby/blob/master/LICENSE)
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### Does Docker run on Linux, macOS, or Windows?
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The Docker Engine client runs natively on Linux, macOS, and Windows. By default,
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these clients connect to a local Docker daemon running in a virtual environment
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managed by Docker, which provides the required features to run Linux-based
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containers within OS X or Windows, and Windows-based containers on Windows.
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If your version of macOS or Windows does not include the required virtualization
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technology, you can use Docker Machine to work around these limitations.
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You can run Windows-based **containers** on Windows Server 2016 and Windows 10.
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Windows-based containers require a Windows kernel to run, in the same way that
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Linux-based containers require a Linux kernel to run. You can even run
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Windows-based containers on a Windows virtual machine running on an macOS or
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Linux host. Docker Machine is not necessary if you run macOS 10.10.3 Yosemite,
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Windows Server 2016, or Windows 10.
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To learn more about Docker on Windows platforms, see the all the topics in
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[Install Docker for Windows](/docker-for-windows/install.md) and
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[Install Docker Enterprise Edition for Windows Server 2016](/engine/installation/windows/docker-ee.md).
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### How do containers compare to virtual machines?
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Containers and virtual machines (VMs) are complementary. VMs excel at providing
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extreme isolation (for example with hostile tenant applications where you need
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the ultimate break out prevention). Containers operate at the process level,
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which makes them very lightweight and perfect as a unit of software delivery.
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While VMs take minutes to boot, containers can often be started in less than a
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second.
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Docker Inc. builds products that let you build and run containers on Linux, Windows and macOS.
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### What does Docker technology add to just plain LXC?
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@ -83,7 +43,7 @@ offers a high-level tool with several powerful functionalities:
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- *Automatic build.* Docker includes [*a tool for developers to automatically
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assemble a container from their source
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code*](reference/builder.md), with full control over application
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code*](/engine/reference/commandline/build.md), with full control over application
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dependencies, build tools, packaging etc. They are free to use `make`, `maven`,
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`chef`, `puppet`, `salt,` Debian packages, RPMs, source tarballs, or any
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combination of the above, regardless of the configuration of the machines.
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@ -96,21 +56,20 @@ offers a high-level tool with several powerful functionalities:
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uploads and downloads, similar to `git pull`, so new versions of a container
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can be transferred by only sending diffs.
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- *Component re-use.* Any container can be used as a [*"parent image"*](reference/glossary.md#image) to create more specialized components. This can
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be done manually or as part of an automated build. For example you can prepare
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the ideal Python environment, and use it as a base for 10 different
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applications. Your ideal PostgreSQL setup can be re-used for all your future
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projects. And so on.
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- *Component re-use.* Any container can be used as a [*"parent image"*](/glossary.md?term=image) to
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create more specialized components. This can be done manually or as part of an
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automated build. For example you can prepare the ideal Python environment, and
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use it as a base for 10 different applications. Your ideal PostgreSQL setup can
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be re-used for all your future projects. And so on.
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- *Sharing.* Docker has access to a public registry [on Docker Hub](https://hub.docker.com/)
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where thousands of people have uploaded useful images: anything from Redis,
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CouchDB, PostgreSQL to IRC bouncers to Rails app servers to Hadoop to base
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images for various Linux distros. The
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[*registry*](/registry/) also
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includes an official "standard library" of useful containers maintained by the
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Docker team. The registry itself is open-source, so anyone can deploy their own
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registry to store and transfer private containers, for internal server
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deployments for example.
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- *Sharing.* Docker has access to a public registry [on Docker
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Hub](https://hub.docker.com/){: target="_blank" class="_"} where thousands of
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people have uploaded useful images: anything from Redis, CouchDB, PostgreSQL to
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IRC bouncers to Rails app servers to Hadoop to base images for various Linux
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distros. The [*registry*](/registry/) also includes an official "standard
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library" of useful containers maintained by the Docker team. The registry itself
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is open-source, so anyone can deploy their own registry to store and transfer
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private containers, for internal server deployments for example.
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- *Tool ecosystem.* Docker defines an API for automating and customizing the
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creation and deployment of containers. There are a huge number of tools
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@ -124,7 +83,7 @@ offers a high-level tool with several powerful functionalities:
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### What is different between a Docker container and a VM?
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There's a great StackOverflow answer [showing the differences](
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http://stackoverflow.com/questions/16047306/how-is-docker-io-different-from-a-normal-virtual-machine).
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http://stackoverflow.com/questions/16047306/how-is-docker-io-different-from-a-normal-virtual-machine){: target="_blank" class="_"}.
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### Do I lose my data when the container exits?
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@ -136,16 +95,13 @@ container persists even after the container halts.
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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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Heroku run on container technology, at a scale of hundreds of
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thousands or even millions of containers.
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### How do I connect Docker containers?
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Currently the recommended way to connect containers is via the Docker network feature. You can see details of how to [work with Docker networks here](userguide/networking/work-with-networks.md).
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Also useful for more flexible service portability is the [Ambassador linking
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pattern](admin/ambassador_pattern_linking.md).
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### How do I run more than one process in a Docker container?
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This approach is discouraged for most use cases. For maximum efficiency and
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@ -183,12 +139,12 @@ You can learn about the project's security policy
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### Why do I need to sign my commits to Docker with the DCO?
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Please read [our blog post](
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http://blog.docker.com/2014/01/docker-code-contributions-require-developer-certificate-of-origin/) on the introduction of the DCO.
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http://blog.docker.com/2014/01/docker-code-contributions-require-developer-certificate-of-origin/){: target="_blank" class="_"} on the introduction of the DCO.
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### When building an image, should I prefer system libraries or bundled ones?
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*This is a summary of a discussion on the [docker-dev mailing list](
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https://groups.google.com/forum/#!topic/docker-dev/L2RBSPDu1L0).*
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https://groups.google.com/forum/#!topic/docker-dev/L2RBSPDu1L0){: target="_blank" class="_"}.*
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Virtually all programs depend on third-party libraries. Most frequently, they
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will use dynamic linking and some kind of package dependency, so that when
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@ -206,9 +162,9 @@ The key point about system libraries is not about saving disk or memory space.
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It is about security. All major distributions handle security seriously, by
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having dedicated security teams, following up closely with published
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vulnerabilities, and disclosing advisories themselves. (Look at the [Debian
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Security Information](https://www.debian.org/security/) for an example of those
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procedures.) Upstream developers, however, do not always implement similar
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practices.
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Security Information](https://www.debian.org/security/){: target="_blank"
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class="_"} for an example of those procedures.) Upstream developers, however, do
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not always implement similar practices.
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Before setting up a Docker image to compile a program from source, if you want
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to use bundled libraries, you should check if the upstream authors provide a
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@ -220,7 +176,8 @@ Likewise, before using packages built by others, you should check if the
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channels providing those packages implement similar security best practices.
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Downloading and installing an "all-in-one" .deb or .rpm sounds great at first,
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except if you have no way to figure out that it contains a copy of the OpenSSL
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library vulnerable to the [Heartbleed](http://heartbleed.com/) bug.
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library vulnerable to the [Heartbleed](http://heartbleed.com/){: target="_blank"
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class="_"} bug.
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### Why is `DEBIAN_FRONTEND=noninteractive` discouraged in Dockerfiles?
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@ -250,7 +207,7 @@ Because of this, and because setting `DEBIAN_FRONTEND` to `noninteractive` is
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mainly a 'cosmetic' change, we *discourage* changing it.
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If you *really* need to change its setting, make sure to change it back to its
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[default value](https://www.debian.org/releases/stable/i386/ch05s03.html.en)
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[default value](https://www.debian.org/releases/stable/i386/ch05s03.html.en){: target="_blank" class="_"}
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afterwards.
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### Why do I get `Connection reset by peer` when making a request to a service running in a container?
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@ -263,9 +220,10 @@ how to do this, check the documentation for your OS.
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### Why do I get `Cannot connect to the Docker daemon. Is the docker daemon running on this host?` when using docker-machine?
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This error points out that the docker client cannot connect to the virtual machine.
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This means that either the virtual machine that works underneath `docker-machine`
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is not running or that the client doesn't correctly point at it.
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This error points out that the docker client cannot connect to the virtual
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machine. This means that either the virtual machine that works underneath
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`docker-machine` is not running or that the client doesn't correctly point at
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it.
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To verify that the docker machine is running you can use the `docker-machine ls`
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command and start it with `docker-machine start` if needed.
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@ -286,12 +244,11 @@ You have to tell Docker to talk to that machine. You can do this with the
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You can find more answers on:
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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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- [Docker user mailinglist](https://groups.google.com/d/forum/docker-user){: target="_blank" class="_"}
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- [Docker developer mailinglist](https://groups.google.com/d/forum/docker-dev){: target="_blank" class="_"}
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- [IRC, docker on freenode](irc://chat.freenode.net#docker)
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- [GitHub](https://github.com/moby/moby)
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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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- [GitHub](https://github.com/moby/moby){: target="_blank" class="_"}
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- [Ask questions on Stackoverflow](http://stackoverflow.com/search?q=docker){: target="_blank" class="_"}
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- [Join the conversation on Twitter](http://twitter.com/docker){: target="_blank" class="_"}
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Looking for something else to read? Checkout the [User Guide](userguide/index.md).
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