Server provisioning with Vagrant, CoreOS and Docker

In this article, we'll see how easy it is to build a custum Linux image an to deploy it in cloud using modern DevOps tools like Vagrant, CoreOS and Docker and the Amazon Web Services cloud provider.

Setup Vagrant and CoreOS

To build a custom Linux image for Docker we need to run Docker on Linux... ;-) CoreOS is a minimalist Linux distribution that ships with Docker and a few other services. As we want to setup our custom Linux image for Docker locally, let use CoreOS with Vagrant. Vagrant is about provisionning virtual development environment and it's exactly what we need to launch CoreOS quickly on Windows, Mac OS X or Linux. To get all this stuff to work together just follow the Running CoreOS on Vagrant documentation on the CoreOs website.

git clone https://github.com/coreos/coreos-vagrant.git
cd coreos-vagrant
vagrant up
Bringing machine 'core-01' up with 'virtualbox' provider...
==> core-01: Checking if box 'coreos-beta' is up to date...
==> core-01: Clearing any previously set network interfaces...
==> core-01: Preparing network interfaces based on configuration...
    core-01: Adapter 1: nat
    core-01: Adapter 2: hostonly
==> core-01: Forwarding ports...
    core-01: 22 => 2222 (adapter 1)
==> core-01: Running 'pre-boot' VM customizations...
==> core-01: Booting VM...
==> core-01: Waiting for machine to boot. This may take a few minutes...
    core-01: SSH address: 127.0.0.1:2222
    core-01: SSH username: core
    core-01: SSH auth method: private key
    core-01: Warning: Connection timeout. Retrying...
    core-01: Warning: Connection timeout. Retrying...
    core-01: Warning: Connection timeout. Retrying...
    core-01: Warning: Connection timeout. Retrying...
==> core-01: Machine booted and ready!
==> core-01: Setting hostname...
==> core-01: Configuring and enabling network interfaces...
==> core-01: Machine already provisioned. Run `vagrant provision` or use the `--provision`
==> core-01: to force provisioning. Provisioners marked to run always will still run.

You can now SSH to your virtual environnement :

CoreOS (beta)
core@core-01 ~ $

Create a custom Debian image

Once logged into CoreOS, we can see that Docker is available and that no image is available yet :

core@core-01 ~ $ docker images
REPOSITORY          TAG                 IMAGE ID

Let start a Debian Linux with Docker container :

core@core-01 ~ $ docker run -t -i debian:7.4 cat /etc/*-release | grep NAME
PRETTY_NAME="Debian GNU/Linux 7 (wheezy)"
NAME="Debian GNU/Linux"

Now we have the Debian Docker image available localy :

core@core-01 ~ $ docker images
REPOSITORY          TAG                 IMAGE ID
debian              7.4                 e565fbbc6033

As we can see, java is unavailable :

core@core-01 ~ $ docker run -t -i debian:7.4 java -version
2014/06/27 14:01:58 exec: "java": executable file not found in $PATH

So, how can we build a custom debian:7.4 based image with java pre-installed ? Nothing simpler than creating a Dockerfile with the necessary command to install the jdk on a debian distribution :

core@core-01 ~ $ touch DockerFile
core@core-01 ~ $ vi DockerFile

FROM debian:7.4
MAINTAINER Antoine Vianey 

RUN apt-get update
RUN apt-get -f install
RUN export DEBIAN_FRONTEND=noninteractive
RUN apt-get -y install --no-install-recommends openjdk-7-jdk

The docker build command builds the image for us... The -t option allow us to specify the repository + tag that will be associated with the resulting image. Read the Dockerfile reference guide for a full description of what you can do with dockerfile.

core@core-01 ~ $ sudo docker build -t avianey/ojdk7-deb .

If every step runs fine the final image is available under the specified tag. If a step fails, interdmediate steps images are kept to speed up the rebuild after having corrected the failing Dockerfile step.

core@core-01 ~ $ docker images
REPOSITORY          TAG                 IMAGE ID
avianey/ojdk7-deb   latest              54e73307f07e
debian              7.4                 e565fbbc6033

Check that java is installed :

core@core-01 ~ $ docker run -t -i avianey/ojdk7-deb java -version
java version "1.7.0_55"
OpenJDK Runtime Environment (IcedTea 2.4.7) (7u55-2.4.7-1~deb7u1)
OpenJDK 64-Bit Server VM (build 24.51-b03, mixed mode)

Everything is fine, we can tag our custom image :

core@core-01 ~ $ sudo docker tag 54e73307f07e avianey/ojdk7-deb:v1

core@core-01 ~ $ docker images
REPOSITORY          TAG                 IMAGE ID
avianey/ojdk7-deb   latest              54e73307f07e
avianey/ojdk7-deb   v1                  54e73307f07e
debian              7.4                 e565fbbc6033

Use the image in the cloud

Now that we have our custom image setup, we need to push it in the Docker Hub or a private Docker repository to use it from the cloud :

core@core-01 ~ $ sudo docker push avianey/ojdk7-deb
The push refers to a repository [avianey/ojdk7-deb] (len: 2)
Sending image list
...
Pushing repository avianey/ojdk7-deb (2 tags)
...
Pushing tag for rev [54e73307f07e] on {https://registry-1.docker.io/v1/repositories/avianey/ojdk7-deb/tags/latest}
Pushing tag for rev [54e73307f07e] on {https://registry-1.docker.io/v1/repositories/avianey/ojdk7-deb/tags/v1}

Everyone can now start a Docker container running the avianey/ojdk7-deb:v1 image. That what we are going to do with a CoreOS Amazon Machine Image :

Using username "core".
Authenticating with public key "imported-openssh-key"
CoreOS (beta)
core@ip-172-31-25-84 ~ $ docker run -t -i avianey/ojdk7-deb:v1 java -version
Unable to find image 'avianey/ojdk7-deb:v1' locally
Pulling repository avianey/ojdk7-deb
54e73307f07e: Download complete
511136ea3c5a: Download complete
405cce5cd17d: Download complete
e565fbbc6033: Download complete
782079a3e1cf: Download complete
3be917c2a827: Download complete
11311a0d3731: Download complete
b4754115da81: Download complete
java version "1.7.0_55"
OpenJDK Runtime Environment (IcedTea 2.4.7) (7u55-2.4.7-1~deb7u1)
OpenJDK 64-Bit Server VM (build 24.51-b03, mixed mode)

That's it, enjoy !