public String getClientFactoryClassName() {
    if (containsKey(CONFIG_KEY_CLIENT_FACTORY)) {
      return get(CONFIG_KEY_CLIENT_FACTORY);
    } else {
      throw new SamzaException("You must specify a client factory class"
                               + " for the Elasticsearch system.");
    }
  }
Elasticsearch configuration class to read elasticsearch specific configuration from Samza.
samza-elasticsearch/src/main/java/org/apache/samza/config/ElasticsearchConfig.java