As originally designed the backup-domain command only backups up the domain
(e.g. contents of the <install dir>/domains/<domain name>). It does not backup
up any instances or nodes that also happen to be configured on the DAS.
I think in production deployments the DAS would generally not have any local
nodes or instances but I could see how a developer would like to be able to
backup the domain, nodes and instances to migrate to a new version.
I'm going to change this issue to an enhancement where backup-domain offers an
option to also backup up nodes on the DAS.