in flume-elasticsearch-sink/src/main/java/org/apache/flume/sink/elasticsearch/client/ElasticSearchTransportClient.java [75:80]
public ElasticSearchTransportClient(String[] hostNames, String clusterName,
ElasticSearchEventSerializer serializer) {
configureHostnames(hostNames);
this.serializer = serializer;
openClient(clusterName);
}