public void writeConfig(String source, Config config) {
    log.debug("Writing config: {}", config);
    for (Map.Entry<String, String> configPair : config.entrySet()) {
      send(new SetConfig(source, configPair.getKey(), configPair.getValue()));
    }
    systemProducer.flush(source);
  }
Helper method that sends a series of SetConfig messages to the coordinator
stream.

@param source
         An identifier to denote which source is sending a message. This
         can be any arbitrary string.
@param config
         The config object to store in the coordinator stream.
samza-core/src/main/java/org/apache/samza/coordinator/stream/CoordinatorStreamSystemProducer.java