Hi Paul,
Be sure you’ve done the manual agent registration (http://docs.hortonworks.com/HDPDocuments/Ambari-1.7.0.0/AMBARI_DOC_SUITE/index.html#Item11.2) for the hosts are you are going to use in the cluster.
And you see what hosts are registered with this call:
http://test-paul-ambari-1.egsense.com:8080/api/v1/hosts
And in case you need it, a wiki resource on Blueprints is here:
https://cwiki.apache.org/confluence/display/AMBARI/Blueprints
Cheers,
Jeff