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.
"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)
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.
### Linux
You should have at least a 3.8 kernel, but 3.10.x is [recommended](http://docs.docker.com/installation/binaries/#check-kernel-dependencies).
The canonical way to use Docker is with the aid of the boot2docker VM. However, using the out of the box boot2docker doesn't give me control over my Vagrant instances (especially the lack of port forwarding). So here's how to use boot2docker from a Vagrant instance.
We use the [YungSang modified boot2docker instance](https://github.com/YungSang/boot2docker-vagrant-box) from the [Vagrant Cloud](https://vagrantcloud.com/yungsang/boxes/boot2docker):
> NOTE: the YungSang boot2docker opens up port forwarding to the network, so is not safe on public wifi. You can make a good argument that docker without TLS is [fundamentally unsafe](https://medium.com/@kevanahlquist/never-run-docker-on-a-tcp-socket-without-tls-1e7df31cf18c). I only do it because I have [Hands Off](http://www.oneperiodic.com/products/handsoff/) installed to limit external network access.
[Your basic isolated Docker process](http://etherealmind.com/basics-docker-containers-hypervisors-coreos/). Containers are to Virtual Machines as threads are to processes. Or you can think of them as chroots on steroids.
If you want to run and then interact with a container, `docker start`, then spawn a shell as described in [Executing Commands](https://github.com/wsargent/docker-cheat-sheet/#executing-commands).
If you want to map a directory on the host to a docker container, `docker run -v $HOSTDIR:$DOCKERDIR`. Also see [Volumes](https://github.com/wsargent/docker-cheat-sheet/#volumes).
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.
* [`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).
### 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/).
[The configuration file](https://docs.docker.com/reference/builder/). 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.
The [versioned filesystem](http://en.wikipedia.org/wiki/Aufs) in Docker is based on layers. They're like [git commits or changesets for filesystems](https://docs.docker.com/terms/layer/).
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. Container42 is [also helpful](http://container42.com/2014/11/03/docker-indepth-volumes/).
As of 1.3, you can [map MacOS host directories as docker volumes](http://docs.docker.com/userguide/dockervolumes/#mount-a-host-directory-as-a-data-volume) through boot2docker:
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
[Fig](http://www.fig.sh/) is a helper app that makes it easier to run multiple docker containers on the same host. I would expect it to be used during dev/qa more than in production.
Fig works with a ```fig.yml``` file (default name, use ```-f``` to provide a different filename) that defines the containers you wish to use with it. Fig will take its project name from the name of the folder containing your yml configuration but you can override that with the ```-p``` parameter.
Once I have my config defined, I can use ```fig up -d``` to run it (the ```-d``` runs it as a background task). This will build (if required) start and link any containers.
You can do everything you do with fig using docker directly but running multiple containers with parameters would require some sort of script if you plan to do it more than once so the yml config of fig and the convenience commands it provides are worth considering.
Here's an example of setting up a ```fig.yml``` for an app with a apache packaged client container and a tomcat packaged app war:
First, here are the two docker commands to run these containers:
```
docker run -p 8080:8080 -v /Users/me/tomcatwork/trial.properties:/usr/share/tomcat6/trial.properties:rw -d me/tcfull
docker run -p 80:80 -v /Users/me/dockerwork/localproxy.conf:/etc/apache2/conf-enabled/proxy.conf:rw -d me/afull
```
at this point, I haven't linked the containers - I'm using the proxy.conf to specify the tomcat address.
As you can see it follows the docker commands with the addition of names for the containers and a links section for the web container, linking it to the app container.
As part of that linking process, docker will copy any environment variables defined in the app container over to the web container, define new environment variables for the address the app container is running at and also add an app entry in the etc/hosts file for the web container. I can modify my proxy conf to address ```http://app:8080``` and fig/docker will take care of the rest.
I can then use commands like ```fig stop``` and ```fig rm``` to stop all my containers and remove them.
NB - docker will [eventually](https://gist.github.com/aanand/9e7ac7185ffd64c1a91a) absorb figs functionality with docker groups and docker up but it looks like they're keeping the yml config so it should be pretty seamless when it happens.
```fig run``` is a useful command for debugging issues. It allows me to startup a named container (and any it links to) and run a one off command.
This allows me to do things like ```fig run web env``` which will give me a list of all the environment variables that are available on the web container including the ones generated via the link to app.
I can also use ```fig run web bash``` to run my web container interactively the way it has been setup by fig with the link to app so I can debug any issues from the command line.
