public void close() {
    try {
      localClientCache.invalidateAll();
      signers.invalidateAll();
      localClientCache.cleanUp();
      signers.cleanUp();
    } catch (Exception ex) {
      LOG.error("Error closing the coordinator; ignoring", ex);
    }
  }
We'll keep signers per cluster around for some time, for reuse.
llap-client/src/java/org/apache/hadoop/hive/llap/coordinator/LlapCoordinator.java