public void swapInstance(String clusterName, String oldInstanceName, String newInstanceName) {
ZKHelixDataAccessor accessor =
new ZKHelixDataAccessor(clusterName, new ZkBaseDataAccessor<ZNRecord>(_zkClient));
Builder keyBuilder = accessor.keyBuilder();
InstanceConfig oldConfig = accessor.getProperty(keyBuilder.instanceConfig(oldInstanceName));
if (oldConfig == null) {
String error = "Old instance " + oldInstanceName + " does not exist, cannot swap";
_logger.warn(error);
throw new HelixException(error);
}