Restarting the master cluster controller changes the url sent to the nodes to contact the metadata service to http://localhost/MAAS; this prevents the nodes from booting properly.

[Raphaël Badin]

The first start of the master cluster controller (the cluster controller installed alongside the region controller) works fine but as soon as the master cluster controller is restarted (which happens when the package is upgraded for instance), the url used to tell to booting nodes how to reach the metadata server becomes 'http://localhost/MAAS'. This makes the nodes unable to fetch metadata information.

See
http://paste.ubuntu.com/1537196/

The master cluster controller should not change the url stored in the corresponding NodeGroup.maas_url, instead, it should leave it empty so that the value of DEFAULT_MAAS_URL will be used when building the url to give to the nodes for them to access the MAAS server.