@Override
 public byte[] serialize(ServiceInstance<DrillbitEndpoint> i) throws Exception {
   DrillServiceInstance.Builder b = DrillServiceInstance.newBuilder();
   b.setId(i.getId());
   b.setRegistrationTimeUTC(i.getRegistrationTimeUTC());
   b.setEndpoint(i.getPayload());
   return b.build().toByteArray();
 }