private void sendSetConfigMessage(String key, String value) {
    log.info("sent SetConfig message with key = " + key + " and value = " + value);
    coordinatorStreamSystemProducer.send(new SetConfig(CoordinatorStreamWriter.SOURCE, key, value));
  }
This method sends message of type "set-config" to the coordinator stream

@param key   defines the name of the configuration being set. For example, for setting the number of yarn containers,
             the key is "yarn.container.count"
@param value defines the value associated with the key. For example, if the key is "yarn.container.count" the value
             is the new number of containers.
samza-core/src/main/java/org/apache/samza/coordinator/stream/CoordinatorStreamWriter.java