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150 lines
6.2 KiB
Markdown
page_title: About Docker
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page_description: Introduction to Docker.
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page_keywords: docker, introduction, documentation, about, technology, understanding, Dockerfile
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# About Docker
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**Develop, Ship and Run Any Application, Anywhere**
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[**Docker**](https://www.docker.com) is a platform for developers and sysadmins
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to develop, ship, and run applications. Docker lets you quickly assemble
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applications from components and eliminates the friction that can come when
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shipping code. Docker lets you get your code tested and deployed into production
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as fast as possible.
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Docker consists of:
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* The Docker Engine - our lightweight and powerful open source container
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virtualization technology combined with a work flow for building
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and containerizing your applications.
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* [Docker Hub](https://hub.docker.com) - our SaaS service for
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sharing and managing your application stacks.
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## Why Docker?
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*Faster delivery of your applications*
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* We want your environment to work better. Docker containers,
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and the work flow that comes with them, help your developers,
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sysadmins, QA folks, and release engineers work together to get your code
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into production and make it useful. We've created a standard
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container format that lets developers care about their applications
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inside containers while sysadmins and operators can work on running the
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container in your deployment. This separation of duties streamlines and
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simplifies the management and deployment of code.
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* We make it easy to build new containers, enable rapid iteration of
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your applications, and increase the visibility of changes. This
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helps everyone in your organization understand how an application works
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and how it is built.
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* Docker containers are lightweight and fast! Containers have
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sub-second launch times, reducing the cycle
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time of development, testing, and deployment.
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*Deploy and scale more easily*
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* Docker containers run (almost) everywhere. You can deploy
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containers on desktops, physical servers, virtual machines, into
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data centers, and up to public and private clouds.
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* Since Docker runs on so many platforms, it's easy to move your
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applications around. You can easily move an application from a
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testing environment into the cloud and back whenever you need.
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* Docker's lightweight containers also make scaling up and
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down fast and easy. You can quickly launch more containers when
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needed and then shut them down easily when they're no longer needed.
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*Get higher density and run more workloads*
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* Docker containers don't need a hypervisor, so you can pack more of
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them onto your hosts. This means you get more value out of every
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server and can potentially reduce what you spend on equipment and
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licenses.
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*Faster deployment makes for easier management*
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* As Docker speeds up your work flow, it gets easier to make lots
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of small changes instead of huge, big bang updates. Smaller
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changes mean reduced risk and more uptime.
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## About this guide
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The [Understanding Docker section](introduction/understanding-docker.md) will help you:
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- See how Docker works at a high level
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- Understand the architecture of Docker
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- Discover Docker's features;
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- See how Docker compares to virtual machines
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- See some common use cases.
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### Installation Guides
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The [installation section](/installation/#installation) will show you how to install
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Docker on a variety of platforms.
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### Docker User Guide
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To learn about Docker in more detail and to answer questions about usage and
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implementation, check out the [Docker User Guide](/userguide/).
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## Release Notes
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**Version 1.2.0**
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This version fixes a number of bugs and issues and adds new functions and other
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improvements. These include:
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*New restart policies*
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We added a `--restart flag` to `docker run` to specify a restart policy for your
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container. Currently, there are three policies available:
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* `no` – Do not restart the container if it dies. (default)
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* `on-failure` – Restart the container if it exits with a non-zero exit code.
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This can also accept an optional maximum restart count (e.g. `on-failure:5`).
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* `always` – Always restart the container no matter what exit code is returned.
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This deprecates the `--restart` flag on the Docker daemon.
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*New flags for `docker run`: `--cap-add` and `–-cap-drop`*
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In previous releases, Docker containers could either be given complete capabilities or
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they could all follow a whitelist of allowed capabilities while dropping all others.
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Further, using `--privileged` would grant all capabilities inside a container, rather than
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applying a whitelist. This was not recommended for production use because it’s really
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unsafe; it’s as if you were directly in the host.
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This release introduces two new flags for `docker run`, `--cap-add` and `--cap-drop`, that
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give you fine-grain control over the specific capabilities you want grant to a particular
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container.
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*New `-–device` flag for `docker run`*
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Previously, you could only use devices inside your containers by bind mounting them (with
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`-v`) in a `--privileged` container. With this release, we introduce the `--device flag`
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to `docker run` which lets you use a device without requiring a privileged container.
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*Writable `/etc/hosts`, `/etc/hostname` and `/etc/resolv.conf`*
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You can now edit `/etc/hosts`, `/etc/hostname` and `/etc/resolve.conf` in a running
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container. This is useful if you need to install BIND or other services that might
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override one of those files.
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Note, however, that changes to these files are not saved when running `docker build` and
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so will not be preserved in the resulting image. The changes will only “stick” in a
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running container.
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*Docker proxy in a separate process*
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The Docker userland proxy that routes outbound traffic to your containers now has its own
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separate process (one process per connection). This greatly reduces the load on the
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daemon, which increases stability and efficiency.
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*Other improvements & changes*
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* When using `docker rm -f`, Docker now kills the container (instead of stopping it)
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before removing it . If you intend to stop the container cleanly, you can use `docker
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stop`.
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* Added support for IPv6 addresses in `--dns`
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* Added search capability in private registries
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