NOTE: 534 stars, 106 forks. I love you all. Please contribute tips and edits back to this cheat sheet -- email's will.sargent@gmail.com and you can treat gists like git repositories and send git diffs.
- Why
- I just want a dev environment
- Prerequisites
- Installation
- Containers
- Images
- Registry and Repository
- Dockerfile
- Layers
- Links
- Volumes
- Exposing Ports
- Tips
Why Should I Care (For Developers)
"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."
- A Docker Dev Environment in 24 Hours!
- Building a Development Environment With Docker
- Discourse in a Docker Container
Use Homebrew.
ruby -e "$(curl -fsSL https://raw.github.com/mxcl/homebrew/go)"
This is all MacOS specific.
Install VirtualBox and Vagrant using Brew 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 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
sudo apt-get install -qy docker.io
sudo ln -sf /usr/bin/docker.io /usr/local/bin/docker
Then start up a container:
sudo docker run -i -t ubuntu /bin/bash
That's it, you have a running Docker container.
I use Oh My Zsh with the Docker plugin for autocompletion of docker commands. YMMV.
Your basic isolated Docker process. 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 or runit.
docker run
creates a container.docker stop
stops it.docker start
will start it again.docker restart
restarts a container.docker rm
deletes a container.docker kill
sends a SIGKILL to a container. Has issues.docker attach
will connect to a running container.docker wait
blocks until container stops.
If you want to run and then interact with a container, docker start
then docker attach
to get in.
If you want a transient container, docker run -rm
will remove the container after it stops.
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, 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 section.
docker ps
shows running containers.docker inspect
looks at all the info on a container (including IP address).docker logs
gets logs from container.docker events
gets events from container.docker port
shows public facing port of container.docker top
shows running processes in container.docker diff
shows changed files in the container's FS.
docker ps -a
shows running and stopped containers.
There doesn't seem to be a way to use docker directly to import files into a container's filesystem.
docker cp
copies files or folders out of a container's filesystem.docker export
turns container filesystem into tarball.
Images are just templates for docker containers.
docker images
shows all images.docker import
creates an image from a tarball.docker build
creates image from Dockerfile.docker commit
creates image from a container.docker rmi
removes an image.docker insert
inserts a file from URL into image. (kind of odd, you'd think images would be immutable after create)docker load
loads an image from a tar archive as STDIN, including images and tags (as of 0.7).docker 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.
docker history
shows history of image.docker tag
tags an image to a name (local or registry).
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.
Docker.io hosts its own index to a central registry which contains a large number of repositories.
docker login
to login to a registry.docker search
searches registry for image.docker pull
pulls an image from registry to local machine.docker push
pushes an image to the registry from local machine.
The configuration file. 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 and the best practices / take 2 for more details.
If you use jEdit, I've put up a syntax highlighting module for Dockerfile you can use.
The versioned filesystem in Docker is based on layers. They're like git commits or changesets for filesystems.
Links are how Docker containers talk to each other through TCP/IP ports. Linking into Redis and Atlassian show worked examples. You can also (in 0.11) resolve links by hostname.
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.
If you have a container with the name CONTAINER (specified by docker run -name CONTAINER
) and in the Dockerfile, it has an exposed port:
EXPOSE 1337
Then if we create another container called LINKED like so:
docker run -d -link CONTAINER:ALIAS -name LINKED user/wordpress
Then the exposed ports and aliases of CONTAINER will show up in LINKED with the following environment variables:
$ALIAS_PORT_1337_TCP_PORT
$ALIAS_PORT_1337_TCP_ADDR
And you can connect to it that way.
To delete links, use docker rm -link
.
Docker volumes are free-floating filesystems. They don't have to be connected to a particular container.
Volumes are useful in situations where you can't use links (which are TCP/IP only). For instance, if you need to have two docker instances communicate by leaving stuff on the filesystem.
You can mount them in several docker containers at once, using docker run -volume-from
See advanced volumes for more details.
Exposing ports through the host container is fiddly but doable.
First expose the port in your Dockerfile:
EXPOSE <CONTAINERPORT>
Then map the container port to the host port (only using localhost interface):
docker run -p 127.0.0.1:$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
end
...
end
If you forget what you mapped the port to on the host container, use docker port
to show it:
docker port CONTAINER $CONTAINERPORT
Sources:
alias dl='docker ps -l -q'
docker run ubuntu echo hello world
docker commit `dl` helloworld
docker commit -run='{"Cmd":["postgres", "-too -many -opts"]}' `dl` postgres
docker inspect `dl` | grep IPAddress | cut -d '"' -f 4
or
wget http://stedolan.github.io/jq/download/source/jq-1.3.tar.gz
tar xzvf jq-1.3.tar.gz
cd jq-1.3
./configure && make && sudo make install
docker inspect `dl` | jq -r '.[0].NetworkSettings.IPAddress'
or (this is unverified)
docker inspect -f '{{ .NetworkSettings.IPAddress }}' <container_name>
docker run -rm ubuntu env
docker ps -a | grep 'weeks ago' | awk '{print $1}' | xargs docker rm
docker rm `docker ps -a -q`
docker images -viz | dot -Tpng -o docker.png