flink write to druid by tranquility in exactly-once way

[sydt2014]

When transfer data from flink to druid by tranquility, it is not exactly-once , which it may lost data or has repeated data.Is there some way guarantee exactly-once ?

[gianm]

Would it work to go through Kafka? (Druid ingest from Kafka through the Kafka indexing service is exactly-once)