Assuming this is a Single install --
Log into the container
sudo lxc-ls -f
sudo lxc-attach -n <container> # usually something like uoi-bootstrap
Once in the container
sudo su - ubuntu
export JUJU_HOME=~/.cloud-install/juju
Now you can access your juju environment as normal
juju status
juju ssh nova-cloud-controller/0
...
As far as bringing back up the nodes, you'll need to run a juju status within the container as above and see which services are reporting errors.
If this is a Multi install --
- Export the JUJU_HOME on the machine you ran the installer from
export JUJU_HOME=~/.cloud-install/juju
Perform step 3 from above.