Bootstrapping LXCs behind an APT proxy

Had some fun getting lxc-create to do its stuff this morning, the /etc/default/lxc config file has half a hint but not a whole one:

# MIRROR to be used by ubuntu template at container creation:
# Leaving it undefined is fine
#MIRROR="http://archive.ubuntu.com/ubuntu"
# or 
#MIRROR="http://<host-ip-addr>:3142/archive.ubuntu.com/ubuntu"

# LXC_AUTO - whether or not to start containers symlinked under
# /etc/lxc/auto
LXC_AUTO="true"

# Leave USE_LXC_BRIDGE as "true" if you want to use lxcbr0 for your
# containers.  Set to "false" if you'll use virbr0 or another existing
# bridge, or mavlan to your host's NIC.
USE_LXC_BRIDGE="true"

# If you change the LXC_BRIDGE to something other than lxcbr0, then
# you will also need to update your /etc/lxc/lxc.conf as well as the
# configuration (/var/lib/lxc/<container>/config) for any containers
# already created using the default config to reflect the new bridge
# name.
# If you have the dnsmasq daemon installed, you'll also have to update
# /etc/dnsmasq.d/lxc and restart the system wide dnsmasq daemon.
LXC_BRIDGE="lxcbr0"
LXC_ADDR="10.0.3.1"
LXC_NETMASK="255.255.255.0"
LXC_NETWORK="10.0.3.0/24"
LXC_DHCP_RANGE="10.0.3.2,10.0.3.254"
LXC_DHCP_MAX="253"

LXC_SHUTDOWN_TIMEOUT=120

The line that it's missing is "you'll also need to set the SECURITY_MIRROR field or else it dies halfway" - so add the following to your /etc/default/lxc and you're good to go:

MIRROR="http://IP-OF-PROXY:3142/archive.ubuntu.com/ubuntu"
SECURITY_MIRROR="http://IP-OF-PROXY:3142/security.ubuntu.com/ubuntu"