public static Map<HostResource, ClusterMembership> provisionHosts(NodesSpecification nodesSpecification, 
                                                                      String clusterIdString, 
                                                                      HostSystem hostSystem,
                                                                      ConfigModelContext context) {
        ClusterSpec.Id clusterId = ClusterSpec.Id.from(clusterIdString);
        return nodesSpecification.provision(hostSystem,
                                            ClusterSpec.Type.content,
                                            clusterId,
                                            context.getDeployLogger(),
                                            true,
                                            context.clusterInfo().build());
    }
Returns the total number of nodes below this group
config-model/src/main/java/com/yahoo/vespa/model/content/StorageGroup.java