In your original question, you were sure/specific about the high cpu utilisation of the FTS indexer?
IIRC, for FTS scorch indexes, there aren’t any specific upgrade considerations documented between 6.0.3 to 6.5.
Another thing to note is that - the usage observations in your docker container on a single machine mostly not very relevant for a production cluster.
-as there may be other processes running in your machine than the Couchbase server container racing for resources.
-all services running with in a single container also need to compete for resources against each other.
Though not sure whether you have already applied any cpu configs for the container like ref- https://docs.docker.com/engine/reference/run/#cpuset-constraint
Even if you adopt a docker container based deployment strategy my understanding here is that ,
-Running all service containers in a single node is highly not recommendable for a performance sensitive production systems. Placing all containers on a single physical machine means all containers will compete for the same resources. All containers on a single physical machine also eliminates the built-in protection against CB server node failures with replication when the single physical machine fail, all containers experience unavailability at the same time loosing all replicas.
-Running each couchbase server container on it’s own server machine is recommended for production deployments.