public static Set<HostName> getContentHosts(ApplicationInstanceReference appRef) {
        return apps.stream()
                   .filter(application -> application.reference().equals(appRef))
                   .flatMap(appReference -> appReference.serviceClusters().stream())
                   .filter(VespaModelUtil::isContent)
                   .flatMap(serviceCluster -> serviceCluster.serviceInstances().stream())
                   .map(ServiceInstance::hostName)
                   .collect(Collectors.toSet());
    }
A hardcoded set of applications with one storage cluster with two nodes each.

@author oyving
@author smorgrav
orchestrator/src/test/java/com/yahoo/vespa/orchestrator/DummyServiceMonitor.java