LXC

LXC, or Linux Containers, is a lightweight chroot-style virtual machine emulation in the main Linux kernel; most modern distributions should have it. The LXC Ubuntu Server Guide is very good and contains pretty much all you need to know. A lot of work has been done on 14.04 to make it very simple to get started and now supports unprivileged containers. These instructions assume Ubuntu 14.04 LTS.

Install and set up LXC containers

In sum, we install LXC and create a base container, set it up nicely, then clone project containers from it as required. Here's roughly what I had to do to set up LXC nicely.

sudo apt-get install lxc

Optional: user configuration for unprivileged containers

On Ubuntu 14.04 and later, you can now use unprivileged containers, i.e. you don't need to use sudo all the time, and the containers live in your ~/.local/share/lxc directory. From 15.04 onwards this has been set up for you, but for 14.04 LTS, the Ubuntu Server Guide tells you all you need to know to set this up; the short version is that unprivileged containers use user namespaces, so you need to create a subuid and subgid mapping for your user and allow your user to access the bridge network:

sudo usermod -v 100000-200000 -w 100000-200000 $USER
echo "$USER veth lxcbr0 2" | sudo tee -a /etc/lxc/lxc-usernet

Then configure your user account for LXC containers, :

mkdir -p ~/.config/lxc
echo "lxc.id_map = u 0 100000 65536
lxc.id_map = g 0 100000 65536
lxc.network.type = veth
lxc.network.link = lxcbr0" > ~/.config/lxc/default.conf

Create a base container to serve as a template

The -d -r and -a options are distribution, release, and architecture.

lxc-create -t download -n base -- -d ubuntu -r trusty -a amd64
lxc-start -n base

Log in with the default account, (username ubuntu, password ubuntu), then add yourself as a user with sudo:

sudo adduser username
sudo adduser username sudo

This installs some nifty default guff, fixes the probably broken UTC timezone, and fixes locales BEFORE you install things that expect UTF-8 locales, but in particular PostgreSQL (otherwise you end up with SQL_ASCII encoding and nobody wants that):

sudo apt-get install git bash-completion language-pack-en openssh-server
sudo dpkg-reconfigure tzdata

Set up a SSH shortcut for containers

Back on your host workstation, set up an SSH shortcut. If you add the following to your ~/.ssh/config, you will be able to ssh to your containers nice and easily:

# LXC containers
Host *.lxc
  StrictHostKeyChecking no
  UserKnownHostsFile /dev/null
  ProxyCommand nc $(host $(echo %h | sed "s/\.lxc//g") 10.0.3.1 | tail -1 | awk '{print $NF}') %p

Then one can ssh to the containers by appending .lxc to the container name:

ssh myproject.lxc

and then schlepp your handy stuff over:

scp -rp ~/.bashrc ~/.vim* ~/.gitconfig base.lxc:
scp ~/.ssh/authorized_keys base.lxc:.ssh/authorized_keys

Clone a new project container from the template

Now you should have a useful base container, so clone it for your nifty-kitten project and start it (most usefully in a screen session):

lxc-shutdown -n base
lxc-clone -o base -n nifty-kitten
screen
lxc-start -n nifty-kitten
[Ctrl-a] [d] to detach

ssh nifty-kitten.lxc