I put together a quick write-up using Kafka, Flink and Druid in a pipeline. This has a worked out example with code for Flink. Hope this will help folks trying to join streams coming into Druid. https://meditationsonbigdata.blog/2023/03/09/analysing-transactional-data-using-a-pipeline-with-apache-flink-apache-kafka-and-apache-druid/