@Override
  public Set<InternalDistributedMember> getMembersInSameZone(
      InternalDistributedMember targetMember) {
    Set<InternalDistributedMember> buddyMembers = new HashSet<>();
    if (!redundancyZones.isEmpty()) {
      synchronized (redundancyZones) {
        String targetZone = redundancyZones.get(targetMember);
        for (Map.Entry<InternalDistributedMember, String> entry : redundancyZones.entrySet()) {
          if (entry.getValue().equals(targetZone)) {
            buddyMembers.add(entry.getKey());
          }
        }
      }
    } else {
      buddyMembers.add(targetMember);
      Set<InetAddress> targetAddrs = getEquivalents(targetMember.getInetAddress());
      for (InternalDistributedMember o : getDistributionManagerIds()) {
        if (!Collections.disjoint(targetAddrs, getEquivalents(o.getInetAddress()))) {
          buddyMembers.add(o);
        }
      }
    }
    return buddyMembers;
  }
This is an event reflecting that a InternalDistributedMember may be missing but has not yet
left the system.
geode-core/src/main/java/org/apache/geode/distributed/internal/ClusterDistributionManager.java