moby--moby/docs/sources/index.md

page_title: About Docker page_description: Introduction to Docker. page_keywords: docker, introduction, documentation, about, technology, understanding, Dockerfile

About Docker

Develop, Ship and Run Any Application, Anywhere

Docker is a platform for developers and sysadmins to develop, ship, and run applications. Docker lets you quickly assemble applications from components and eliminates the friction that can come when shipping code. Docker lets you get your code tested and deployed into production as fast as possible.

Docker consists of:

• The Docker Engine - our lightweight and powerful open source container virtualization technology combined with a work flow for building and containerizing your applications.
• Docker Hub - our SaaS service for sharing and managing your application stacks.

Why Docker?

Faster delivery of your applications

• We want your environment to work better. Docker containers, and the work flow that comes with them, help your developers, sysadmins, QA folks, and release engineers work together to get your code into production and make it useful. We've created a standard container format that lets developers care about their applications inside containers while sysadmins and operators can work on running the container in your deployment. This separation of duties streamlines and simplifies the management and deployment of code.
• We make it easy to build new containers, enable rapid iteration of your applications, and increase the visibility of changes. This helps everyone in your organization understand how an application works and how it is built.
• Docker containers are lightweight and fast! Containers have sub-second launch times, reducing the cycle time of development, testing, and deployment.

Deploy and scale more easily

• Docker containers run (almost) everywhere. You can deploy containers on desktops, physical servers, virtual machines, into data centers, and up to public and private clouds.
• Since Docker runs on so many platforms, it's easy to move your applications around. You can easily move an application from a testing environment into the cloud and back whenever you need.
• Docker's lightweight containers also make scaling up and down fast and easy. You can quickly launch more containers when needed and then shut them down easily when they're no longer needed.

Get higher density and run more workloads

• Docker containers don't need a hypervisor, so you can pack more of them onto your hosts. This means you get more value out of every server and can potentially reduce what you spend on equipment and licenses.

Faster deployment makes for easier management

• As Docker speeds up your work flow, it gets easier to make lots of small changes instead of huge, big bang updates. Smaller changes mean reduced risk and more uptime.

About this guide

The Understanding Docker section will help you:

• See how Docker works at a high level
• Understand the architecture of Docker
• Discover Docker's features;
• See how Docker compares to virtual machines
• See some common use cases.

Installation Guides

The installation section will show you how to install Docker on a variety of platforms.

Docker User Guide

To learn about Docker in more detail and to answer questions about usage and implementation, check out the Docker User Guide.

Release Notes

Version 1.2.0

This version fixes a number of bugs and issues and adds new functions and other improvements. These include:

New restart policies

We added a --restart flag to docker run to specify a restart policy for your container. Currently, there are three policies available:

• no – Do not restart the container if it dies. (default)
• on-failure – Restart the container if it exits with a non-zero exit code. This can also accept an optional maximum restart count (e.g. on-failure:5).
• always – Always restart the container no matter what exit code is returned. This deprecates the --restart flag on the Docker daemon.

New flags for docker run: --cap-add and –-cap-drop

In previous releases, Docker containers could either be given complete capabilities or they could all follow a whitelist of allowed capabilities while dropping all others. Further, using --privileged would grant all capabilities inside a container, rather than applying a whitelist. This was not recommended for production use because it’s really unsafe; it’s as if you were directly in the host.

This release introduces two new flags for docker run, --cap-add and --cap-drop, that give you fine-grain control over the specific capabilities you want grant to a particular container.

New -–device flag for docker run

Previously, you could only use devices inside your containers by bind mounting them (with -v) in a --privileged container. With this release, we introduce the --device flag to docker run which lets you use a device without requiring a privileged container.

Writable /etc/hosts, /etc/hostname and /etc/resolv.conf

You can now edit /etc/hosts, /etc/hostname and /etc/resolve.conf in a running container. This is useful if you need to install BIND or other services that might override one of those files.

Note, however, that changes to these files are not saved when running docker build and so will not be preserved in the resulting image. The changes will only “stick” in a running container.

Docker proxy in a separate process

The Docker userland proxy that routes outbound traffic to your containers now has its own separate process (one process per connection). This greatly reduces the load on the daemon, which increases stability and efficiency.

Other improvements & changes

• When using docker rm -f, Docker now kills the container (instead of stopping it) before removing it . If you intend to stop the container cleanly, you can use docker stop.

• Added support for IPv6 addresses in --dns

• Added search capability in private registries