I have been playing around recently with Docker. It could really simplify deployments, creating SAAS services or even creating your own personal PAAS.

What is docker?

Docker is an open-source project to easily create lightweight, portable, self-sufficient containers from any application. The same container that a developer builds and tests on a laptop can run at scale, in production, on VMs, bare metal, OpenStack clusters, public clouds and more.

Containers vs Virtual Machines

Virtual Machines: require a complete operating system image, with allocated resources to run. They take a long time to bootup, and have quite a bit of overhead.

Containers: are much more lightweight, since there is no overhead of a complete virtual environment, with the kernel managing the memory and access to the file system. This also means you can bootup an application in seconds.

Install docker

The simplest method would be to use vagrant to set it up on Mac or Linux. (http://docs.docker.io/en/latest/installation/vagrant/)

Setup with vagrant

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git clone https://github.com/dotcloud/docker.git
cd docker
vagrant up
vagrant ssh

Manual Setup

• Install virtualbox – (https://www.virtualbox.org)
• Launch a new VM, and install ubuntu 12.04 (64 bit) – (http://www.ubuntu.org)

Docker works best with the 3.8 kernel due to a bug in lxc which can cause some issues if you are on 3.2. run uname -r to check which version you are on, and run the following if you are not on 3.8

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sudo apt-get update

sudo apt-get install linux-image-generic-lts-raring linux-headers-generic-lts-raring

sudo reboot

Then run…

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sudo apt-get update

sudo apt-get upgrade

sudo apt-get install python-software-properties git-core build-essentials ssh

sudo apt-get update

sudo add-apt-repository ppa:dotcloud/lxc-docker

sudo apt-get install lxc-docker

Now, hello world… docker style.

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dock@saas:~$ sudo docker run ubuntu /bin/echo hello world
[sudo] password for dock:
Pulling repository ubuntu
Pulling image 8dbd9e392a964056420e5d58ca5cc376ef18e2de93b5cc90e868a1bbc8318c1c (precise) from ubuntu
Pulling image b750fe79269d2ec9a3c593ef05b4332b1d1a02a62b4accb2c21d589ff2f5f2dc (quantal) from ubuntu
Pulling 27cf784147099545 metadata
Pulling 27cf784147099545 fs layer
Downloading 94.86 MB/94.86 MB (100%)
hello world

What just happened?

• docker downloaded the base image from the docker index
• it created a new LXC container
• It allocated a filesystem for it
• Mounted a read-write layer
• Allocated a network interface
• Setup an IP for it, with network address translation
• And then executed a process in there
• Captured its output and printed it to you

In the next post, we will discuss setting up a docker container with mongodb.