How to transport and index Cassandra data on Elastic Search?
Do you want to move the data from Cassandra to ElasticSearch once and only once? Or you want to keep them in sync?
In both cases, I think Storm is a good fit. I used in the past to move data from our RDBMS into Apache Solr. One thing to keep in mind is the limit of writes that Solr/Elastic search can do. If you increased the parallelism, then you are bringing them to the knees.
Another option could be Apache Hadoop but it is only suitable for one time copying or if you want to copy the data (same data of yesterday + what could be new) every day.