PlacementPolicy.yaml

tosca_definitions_version: tosca_simple_yaml_1_0_0_wd03
description: Custom template
template_name: My App
template_version: 0.1.0-SNAPSHOT

imports:
 - tosca-normative-types:1.0.0.wd03-SNAPSHOT

topology_template:
 node_templates:
   a_server:
     type: tosca.nodes.Compute
     properties:
       mem_size: 4 gb
   script_hello:
     type: tosca.nodes.SoftwareComponent
     requirements:
     - host: a_server
     interfaces:
       Standard:
         create: https://raw.githubusercontent.com/ahgittin/tosca-demo/master/script1/scripts/create.sh
         configure: https://raw.githubusercontent.com/ahgittin/tosca-demo/master/script1/scripts/configure.sh
         start: https://raw.githubusercontent.com/ahgittin/tosca-demo/master/script1/scripts/start.sh
         stop: https://raw.githubusercontent.com/ahgittin/tosca-demo/master/script1/scripts/stop.sh  
   JBoss6Server:
     type: org.apache.brooklyn.entity.webapp.jboss.JBoss6Server
     requirements:
     - host: a_server
   CassandraNode:
     type: org.apache.brooklyn.entity.nosql.cassandra.CassandraNode
     requirements:
     - host: a_server

 groups:
   add_brooklyn_location:
     members: [ script_hello, JBoss6Server, CassandraNode ]
     policies:
     - brooklyn.location: aws-ec2:eu-west-1

it should be enough to add_brooklyn_location to the a_server node -- my understanding is that that should correspond to a VM, not a cloud / vm-spec. if you want things to start on separate machine you'd add something like b_server

@ahgittin I am not sure if I understood you.
You mean

groups:
   add_brooklyn_location:
     members: [ a_server ]
     policies:
     - brooklyn.location: aws-ec2:eu-west-1

deploys all nodes on the same VM.
And

groups:
   add_brooklyn_location:
     members: [ a_server, b_server ]
     policies:
     - brooklyn.location: aws-ec2:eu-west-1

will create two different VM, one for a_server and another one for b_server.
Right?