I'd like to control my existing Cassandra cluster with DC/OS. I've done a good amount of research and was only able to find information about setting up a new Cassandra cluster in DC/OS; is there any way to bring these Cassandra machines into a DC/OS cluster and maintain their data? And if so, how can I do that?
Unfortunately, it's not possible as DC/OS cannot "adopt" processes which it didn't start. The only way to move your Cassandra into DC/OS cluster is to install a new Cassandra cluster in DC/OS and migrate data from the old cluster.