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Package:Docker
Docker
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Docker Fun
What is Docker?
Docker is a platform built around linux containers to provide the possibility to build, ship and run distributed applications in containers. It allows users to quickly deploy their applications atop of linux system of their choice in a safe environment. For more information see understanding docker.
Installation
Docker with default use flags needs 'thin' use flag to be set for 'sys-fs/lvm2' ebuild in order to emerge.
(host)# echo '>app-emulation/runc-0.1.0' >> /etc/portage/package.mask (host)# echo 'sys-fs/lvm2 thin' >> /etc/portage/package.use (host)# emerge app-emulation/docker Calculating dependencies... done! [ebuild N ] dev-lang/go-1.3.1 USE="-emacs -vim-syntax -zsh-completion" [ebuild N ] dev-libs/libaio-0.3.110 USE="-static-libs {-test}" [ebuild N ] dev-vcs/mercurial-3.1.1-r1000 USE="-bugzilla -emacs -gpg {-test} -tk" PYTHON_ABIS="2.7 -2.6" [ebuild N ] dev-util/boost-build-1.55.0-r1000 USE="python -examples {-test}" [ebuild N ] dev-libs/boost-1.55.0-r1000 USE="icu nls python threads -c++11 -context -debug -doc -mpi -static-libs -tools" PYTHON_ABIS="2.7 3.3 -2.6 -3.1 -3.2 -3.4 (-3.5)" [ebuild N ] sys-block/thin-provisioning-tools-0.4.0 USE="{-test}" [ebuild N ] sys-fs/lvm2-2.02.103 USE="lvm1 readline static static-libs thin -clvm -cman -lvm2create_initrd (-selinux) -udev" [ebuild N ] app-emulation/docker-1.1.0 USE="contrib device-mapper -aufs -btrfs -doc -lxc -vim-syntax -zsh-completion" ...snip...
If everything went well and no errors appeared during the installation, you're almost ready to go. The only thing that is left is to run the docker daemon.
root # to run docker daemon just once (host)# rc-service docker start root # to run docker on each boot (host)# rc-update add docker default
Playing with Docker
If you want to run docker as regular user, add yourself to docker group
Getting images
The first thing you need is a base image. Base image is a minimal container with an os. You can browse available images on docker hub or through the commandline.
(host)# docker search busybox
NAME DESCRIPTION STARS OFFICIAL AUTOMATED
busybox Busybox base image. 60 [OK]
progrium/busybox 8 [OK]
lgsd/diamond Diamond is the smallest lightweight Docker... 5 [OK]
... snip ...
flynn/busybox Busybox from Ubuntu 13.10 with libc 0
Let's get the official busybox image.
(host)# docker pull busybox
Pulling repository busybox
37fca75d01ff: Download complete
a9eb17255234: Download complete
d200959a3e91: Download complete
fd5373b3d938: Download complete
511136ea3c5a: Download complete
42eed7f1bf2a: Download complete
1f5049b3536e: Download complete
120e218dd395: Download complete
c120b7cab0b0: Download complete
f06b02872d52: Download complete
Running in container
With the image on your drive, you can give it a spin.
(host)# docker run -t -i busybox
-t means you want to allocate a tty for the container -i means the container should be interactive
You are now presented a shell running in the container. You can try looking around. We will now create a new file in the container and leave it.
root ##i## echo 'My hovercraft is full of eels.' > /message root # exit
Listing containers
When the process running in the container ends, the container is stopped. If we were to execute the docker run command again, our message file wouldn't be there, because docker run creates a new container from the base image and runs it. To resume our container, we have to find it's name.
(host)# docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
33dca35dce2a busybox:buildroot-2014.02 "/bin/sh" 6 minutes ago Exited (0) 2 seconds ago clever_goldstine
-a lists all containers, even stopped ones. By default only running are shown
Resuming containers
My busybox container is named clever_goldstine, yours will differ. With this name, we can start the container again.
(host)# docker start clever_goldstine (host)# docker attach clever_goldstine
You are in the container you ran earlier and your file should still be there.
root # cat /message My hovercraft is full of eels.
Stopping containers
(host)# docker stop clever_goldstine
clever_goldstine
Commiting changes
If we consider our changes worth keeping, we can commit them and this resulting image can server as base image for another container. We can also specify the repository and tag for the container.
(host)# docker commit clever_goldstine busybox:message a168a8241324f5c98cc3c5ffdb42a44aa0d0f67bba03a6e27ebbc566108aeebe (host)# docker images REPOSITORY TAG IMAGE ID CREATED VIRTUAL SIZE busybox message ee7b96d88faf 6 seconds ago 2.433 MB busybox buildroot-2013.08.1 d200959a3e91 3 months ago 2.489 MB busybox ubuntu-14.04 37fca75d01ff 3 months ago 5.609 MB busybox ubuntu-12.04 fd5373b3d938 3 months ago 5.455 MB busybox latest a9eb17255234 3 months ago 2.433 MB
As you can see, our container is now prepared as an image for further usage in repository busybox with tag message.
Using Dockerfile
To create an image identical to our busybox:message, one could use the Dockerfile. Dockerfile is a 'recipe' on how to make an image. It contains a series of instructions which are one by one applied to the FROM image. Using Dockerfile is recommended over the run-change-commit workflow.
(host)# cat > Dockerfile <<-EOF FROM busybox:latest RUN echo 'My hovercraft is full of eels.' > /message EOF (host)# docker build -t busybox:message . Sending build context to Docker daemon 2.56 kB Sending build context to Docker daemon Step 0 : FROM busybox:latest ---> a9eb17255234 Step 1 : RUN echo 'My hovercraft is full of eels.' > /message ---> Running in 4473ad720fa4 ---> 6c9bb6eeb7ec Removing intermediate container 4473ad720fa4 Successfully built 6c9bb6eeb7ec
The image should be identical (in contents) to our previous busybox:message one.
Deleting containers
clever_goldstine was a trusty companion but time has come the bid farewell.
(host)# docker rm clever_goldstine
clever_goldstine
To remove all containers, issue docker rm $(docker ps -a -q)
Deleting images
The image we created is cool and all, but pretty much useless so we can delete it.
(host)# docker rmi busybox:message
Untagged: busybox:message
Deleted: 6c9bb6eeb7ecc32418fe7f42bd317c9b15e2b1f9f2aa7cf15ac6dd24700225d0
To remove all images, issue docker rmi $(docker images -q)
Playing with Docker for the brave
Volumes
Docker can attach a directory from the host machine to the container. We can specify a volume for the docker run command in the form of -v /local/directory:/container/directory.
(host)# mkdir /tmp/docker-volume (host)# echo 'Some content' > /tmp/docker-volume/message (host)# docker run -v /tmp/docker-volume:/opt/data -t -i busybox root # ls /opt/data message root # cat /opt/data/message Some content