code: @Override
    public List<String> getRunningMasters() {
      final ZooKeeperClient client = provider.get("getRunningMasters");
      try {
        final List<String> masters = client.getChildren(Paths.statusMaster());
        final ImmutableList.Builder<String> upMasters = ImmutableList.builder();
        for (final String master : masters) {
          if (client.exists(Paths.statusMasterUp(master)) != null) {
            upMasters.add(master);
          }
        }
        return upMasters.build();
      } catch (KeeperException e) {
        throw new HeliosRuntimeException("listing masters failed", e);
      }
    }
docs: Returns a list of the host names of the currently running masters.