On up to date precise, if I am running libvirt with the non-default network of 192.168.123.1, juju-create does not honor this. It is hard-coded to use:
cat <<EOF >> /etc/apt/apt.conf.d/02juju-apt-proxy
Acquire::http { Proxy "http://192.168.122.1:3142"; };
EOF
...
cat <<EOF > /etc/resolvconf/run/resolv.conf
nameserver 192.168.122.1
EOF
cat <<EOF > /etc/resolvconf/resolv.conf.d/base
nameserver 192.168.122.1
EOF
...
It would be best if this could be autodetected. An alternative would be to make this configurable by sourcing a file since juju-create is a shell script.
As a workaround I can edit /usr/share/pyshared/juju/lib/lxc/data/juju-create to use the address I need. This obviously breaks on every upgrade (since this is a custom script, maybe the solution is to move juju-create to /etc/juju and make it a conffile). Seems for this to work I need to 'sudo juju destroy-environment ; juju bootstrap' and then 'juju deploy' something.
Part of moving to using the cloud images for LXC will be to ditch the libvirt tie-in and use lxc's networking instead.