in flink-connector-opensearch/src/main/java/org/apache/flink/streaming/connectors/opensearch/OpensearchSink.java [329:337]
public void open(Configuration parameters) throws Exception {
client = createClient();
bulkProcessor = buildBulkProcessor(new BulkProcessorListener());
requestIndexer =
new OpensearchBulkProcessorIndexer(
bulkProcessor, flushOnCheckpoint, numPendingRequests);
failureRequestIndexer = new BufferingNoOpRequestIndexer();
opensearchSinkFunction.open();
}