NOTE: This used to be a gist that continually expanded. It's now a github project because it's considerably easier for other people to edit, fix and expand on Docker using Github. Just click [README.md](https://github.com/wsargent/docker-cheat-sheet/blob/master/README.md), and then on the "writing pen" icon on the right to edit.
"Docker interests me because it allows simple environment isolation and repeatability. I can create a run-time environment once, package it up, then run it again on any other machine. Furthermore, everything that runs in that environment is isolated from the underlying host (much like a virtual machine). And best of all, everything is fast and simple." --
"With Docker, developers can build any app in any language using any toolchain. “Dockerized” apps are completely portable and can run anywhere - colleagues’ OS X and Windows laptops, QA servers running Ubuntu in the cloud, and production data center VMs running Red Hat.
Developers can get going quickly by starting with one of the 13,000+ apps available on Docker Hub. Docker manages and tracks changes and dependencies, making it easier for sysadmins to understand how the apps that developers build work. And with Docker Hub, developers can automate their build pipeline and share artifacts with collaborators through public or private repositories.
Docker helps developers build and ship higher-quality applications, faster." -- [What is Docker](https://www.docker.com/whatisdocker/#copy1)
Install VirtualBox and Vagrant using [Brew Cask](https://github.com/phinze/homebrew-cask).
```
brew tap caskroom/homebrew-cask
brew install brew-cask
brew cask install virtualbox
brew cask install vagrant
```
I personally don't use boot2docker because I already know how to use Vagrant, and I don't like how boot2docker doesn't give me control over my Vagrant instances (especially the lack of port forwarding). So this is the real way to do it.
We use the [Open Vagrant files](https://github.com/phusion/open-vagrant-boxes) defined by Phusion, which have better default settings:
```
vagrant init phusion/ubuntu-14.04-amd64
vagrant up
vagrant ssh
```
Once you're in the Vagrant instance, install Docker like any other package:
```
sudo apt-get update
sudo apt-get install -qy software-properties-common # needed for add-apt-repository etc
That's it, you have a running Docker container. Also note that Vagrant 1.6 has Docker [supported as a built-in provisioner](https://docs.vagrantup.com/v2/docker/index.html) which can help you when configuring images.
I use [Oh My Zsh](https://github.com/robbyrussell/oh-my-zsh) with the [Docker plugin](https://github.com/robbyrussell/oh-my-zsh/wiki/Plugins#docker) for autocompletion of docker commands. YMMV.
## Containers
[Your basic isolated Docker process](http://docker.readthedocs.org/terms/container/#container-def). Containers are to Virtual Machines as threads are to processes. Or you can think of them as chroots on steroids.
Some common misconceptions it's worth correcting:
* __Containers are not transient__. `docker run` doesn't do what you think.
* __Containers are not limited to running a single command or process.__ You can use [supervisord](http://docs.docker.io/examples/using_supervisord/) or [runit](https://github.com/phusion/baseimage-docker).
If you want to poke around in an image, `docker run -t -i <myimage> <myshell>` to open a tty.
If you want to map a directory on the host to a docker container, `docker run -v $HOSTDIR:$DOCKERDIR` (also see Volumes section).
If you want to integrate a container with a [host process manager](http://docs.docker.io/use/host_integration/), start the daemon with `-r=false` then use `docker start -a`.
If you want to expose container ports through the host, see the [exposing ports](https://github.com/wsargent/docker-cheat-sheet#exposing-ports) section.
There doesn't seem to be a way to use docker directly to import files into a container's filesystem. The closest thing is to mount a host file or directory as a data volume and copy it from inside the container.
The "official" way to enter a docker container while it's running is to use `nsenter`, which uses [libcontainer under the hood](http://jpetazzo.github.io/2014/03/23/lxc-attach-nsinit-nsenter-docker-0-9/). Using an `sshd` daemon is [considered evil](http://jpetazzo.github.io/2014/06/23/docker-ssh-considered-evil/).
Unfortunately, nsenter requires some configuration and installation. If your operating system does not include nsenter (usually in a package named util-linux or similar, although it has to be quite a recent version), the easiest way is probably to install it through docker, as described in the first of the following links:
`nsenter` allows you to run any command (e.g. a shell) inside a container that's already running another command (e.g. your database or webserver). This allows you to see all mounted volumes, check on processes, log files etc. inside a running container.
The first installation method described above also installs a small wrapper script wrapping `nsenter` named `docker-enter` that makes executing a shell inside a running container as easy as `docker-enter CONTAINER` and any other command via `docker-enter CONTAINER COMMAND`.
Images are just [templates for docker containers](http://docker.readthedocs.org/reference/terms/image/).
### Lifecycle
* [`docker images`](http://docs.docker.io/reference/commandline/cli/#images) shows all images.
* [`docker import`](http://docs.docker.io/reference/commandline/cli/#import) creates an image from a tarball.
* [`docker build`](http://docs.docker.io/reference/commandline/cli/#build) creates image from Dockerfile.
* [`docker commit`](http://docs.docker.io/reference/commandline/cli/#commit) creates image from a container.
* [`docker rmi`](http://docs.docker.io/reference/commandline/cli/#rmi) removes an image.
* [`docker insert`](http://docs.docker.io/reference/commandline/cli/#insert) inserts a file from URL into image. (kind of odd, you'd think images would be immutable after create)
* [`docker load`](http://docs.docker.io/reference/commandline/cli/#load) loads an image from a tar archive as STDIN, including images and tags (as of 0.7).
* [`docker save`](http://docs.docker.io/reference/commandline/cli/#save) saves an image to a tar archive stream to STDOUT with all parent layers, tags & versions (as of 0.7).
`docker import` and `docker commit` only set up the filesystem, not Dockerfile info like CMD or ENTRYPOINT or EXPOSE. See [bug](https://github.com/dotcloud/docker/issues/1141).
### Info
* [`docker history`](http://docs.docker.io/reference/commandline/cli/#history) shows history of image.
* [`docker tag`](http://docs.docker.io/reference/commandline/cli/#tag) tags an image to a name (local or registry).
## Registry & Repository
A repository is a *hosted* collection of tagged images that together create the file system for a container.
A registry is a *host* -- a server that stores repositories and provides an HTTP API for [managing the uploading and downloading of repositories](http://docs.docker.io/use/workingwithrepository/).
Docker.io hosts its own [index](https://index.docker.io/) to a central registry which contains a large number of repositories.
* [`docker login`](http://docs.docker.io/reference/commandline/cli/#login) to login to a registry.
* [`docker search`](http://docs.docker.io/reference/commandline/cli/#search) searches registry for image.
* [`docker pull`](http://docs.docker.io/reference/commandline/cli/#pull) pulls an image from registry to local machine.
* [`docker push`](http://docs.docker.io/reference/commandline/cli/#push) pushes an image to the registry from local machine.
## Dockerfile
[The configuration file](http://docs.docker.io/introduction/working-with-docker/#working-with-the-dockerfile). Sets up a Docker container when you run `docker build` on it. Vastly preferable to `docker commit`.
Best to look at [http://github.com/wsargent/docker-devenv](http://github.com/wsargent/docker-devenv) and the [best practices](http://crosbymichael.com/dockerfile-best-practices.html) / [take 2](http://crosbymichael.com/dockerfile-best-practices-take-2.html) for more details.
If you use [jEdit](http://jedit.org), I've put up a syntax highlighting module for [Dockerfile](https://github.com/wsargent/jedit-docker-mode) you can use.
## Layers
The [versioned filesystem](http://en.wikipedia.org/wiki/Aufs) in Docker is based on layers. They're like [git commits or changesets for filesystems](http://docker.readthedocs.org/reference/terms/layer/).
## Links
Links are how Docker containers talk to each other [through TCP/IP ports](http://docs.docker.io/use/working_with_links_names/). [Linking into Redis](http://docs.docker.io/use/working_with_links_names/#links-service-discovery-for-docker) and [Atlassian](http://blogs.atlassian.com/2013/11/docker-all-the-things-at-atlassian-automation-and-wiring/) show worked examples. You can also (in 0.11) resolve [links by hostname](http://docs.docker.io/use/working_with_links_names/#resolving-links-by-name).
NOTE: If you want containers to ONLY communicate with each other through links, start the docker daemon with `-icc=false` to disable inter process communication.
Docker volumes are [free-floating filesystems](http://docs.docker.com/userguide/dockervolumes/). They don't have to be connected to a particular container.
Volumes are useful in situations where you can't use links (which are TCP/IP only). For instance, if you need to have two docker instances communicate by leaving stuff on the filesystem.
You can mount them in several docker containers at once, using `docker run -volume-from`
Because volumes are isolated filesystems, they are often used to store state from computations between transient containers. That is, you can have a stateless and transient container run from a recipe, blow it away, and then have a second instance of the transient container pick up from where the last one left off.
See [advanced volumes](http://crosbymichael.com/advanced-docker-volumes.html) for more details.
## Exposing ports
Exposing ports through the host container is [fiddly but doable](http://docs.docker.io/use/port_redirection/#binding-a-port-to-an-host-interface).
First expose the port in your Dockerfile:
```
EXPOSE <CONTAINERPORT>
```
Then map the container port to the host port (only using localhost interface):
```
docker run -p 127.0.0.1:$HOSTPORT:$CONTAINERPORT --name CONTAINER -t someimage
```
If you're running Docker in Virtualbox, you then need to forward the port there as well. It can be useful to define something in Vagrantfile to expose a range of ports so that you can dynamically map them:
```
Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
...
(49000..49900).each do |port|
config.vm.network :forwarded_port, :host => port, :guest => port
