Docker test drive - the sane way

Introduction

Would you like to try Docker effortlessly on a standard Centos or Ubuntu machine? The summary below will take you there. These instructions work both on physical and virtual machines and will get you Docker containers working in a couple of minutes.

Installation

Centos 6.x
Requirements: EPEL repo, kernel >= 2.6.32-431

yum install docker-io
service docker start
chkconfig docker on

Ubuntu 14.04

wget -qO- https://get.docker.com/ | sh

Test run

 docker run hello-world

Ubuntu 14.04 minimal guest

 Download image, create a container that stays running, run a shell on it:

docker pull ubuntu
MYHOSTNAME=ubuntu01
docker create --name=$MYHOSTNAME --hostname=$MYHOSTNAME ubuntu sleep infinity
docker start  $MYHOSTNAME
docker exec -it $MYHOSTNAME bash

 Create a non-root user and enable ssh on the container

apt-get update
apt-get install -y openssh-server
useradd -m -s /bin/bash myuser
passwd myuser
sed -ri 's/^session\s+required\s+pam_loginuid.so$/session optional pam_loginuid.so/' /etc/pam.d/sshd
service ssh start
exit

Stop the the container in order to test the startup procedure

docker stop $MYHOSTNAME

 Test the container startup procedure and try to access it using ssh

docker start  $MYHOSTNAME
docker exec  $MYHOSTNAME service ssh start
GUESTIP=`docker exec $MYHOSTNAME ip -4 -o  addr  list eth0 label eth0 | awk '{print $4}' | awk -F/ '{print $1}'`
ssh myuser@$GUESTIP

Done! We have a simple procedure to create as many Ubuntu 14.04 general purpose guests as needed using Docker technology.

Final notes

This article aims to be the Docker test drive I haven't found elsewhere. It provides a basic OpenSSH server installation and deals with the exit-after-start nonsense discussed here - the "sleep infinity" command is there to ensure the container stays running until it is explicitly stopped. For other purposes the default behaviour might be better but this is what makes sense in a Docker test drive, especially for people with a virtualization background.
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