private Collection<HostResource> allocateHosts(HostSystem hostSystem, String clusterId, NodesSpecification nodesSpecification) {
        return nodesSpecification.provision(hostSystem, 
                                            ClusterSpec.Type.admin, 
                                            ClusterSpec.Id.from(clusterId), 
                                            context.getDeployLogger(),
                                            false,
                                            context.clusterInfo().build())
                                 .keySet();
    }
Builds the admin model from a version 4 XML tag, or as a default when an admin 3 tag or no admin tag is used.

@author bratseth
config-model/src/main/java/com/yahoo/vespa/model/builder/xml/dom/DomAdminV4Builder.java