I have a Cassandra cluster with 6 nodes, 3 are in the main Cassandra DC, and 3 are in an Analytics DC. I no longer need the Analytics DC, and I want to decommission it. I want to make sure I am doing it safely, in that I do not want to affect the Cassandra DC or my clients. I have only one keyspace that is replicated across the DC's, and I was planning to use ALTER KEYSPACE to simply remove the replication to the Analytics DC. After that, I'd just terminate the Analytics nodes in ec2. Is this a safe plan?
1) Use ALTER KEYSPACE to remove the analytics DC from the replication strategy.
2) Use nodetool decommission to safely remove those nodes from the cluster (one at a time, ideally). They'll no longer own any data, so they'll have nothing to stream to their neighbors.
3) Terminate the instances.