@Override
    public Set<LlapServiceInstance> getByHost(String host) {
      Set<LlapServiceInstance> byHost = new HashSet<LlapServiceInstance>();
      LlapServiceInstance inst = getInstance(getWorkerIdentity(host));
      if (inst != null) {
        byHost.add(inst);
      }
      return byHost;
    }
A single instance in an Llap Service.
llap-client/src/java/org/apache/hadoop/hive/llap/registry/impl/LlapFixedRegistryImpl.java