++ Expanding this question, with our use case, where we justify why we also consider that primary sahrd rebalancing is needed.
In other threads this has been answered as not being necessary saying that primary balancing wont matter that much as primary and replica shards should be carrying equivalents loads.
But building over @oraclept question, we have a use case where this is not true, and primaries are doing a much harder work, so if primaries arenot balanced some nodes can be completely overloaded while others are idle.
Consider for instance a heavy index scenario, where indexing involves upserting (and sadly upserting cant be avoided in our case).
As part of indexing, primary shards have to query the data and do the upsert logic, and later propagate the changes to the replicas.
Replicas dont need to execute the upserting logic, resulting in that primaries work is much heavier than replicas, so that the workload on the cluster is as unbalanced as the primary shards are.
So, we also wonder ifs it possible to have primaries balanced on a cluster, automatically or executing some kind of procedure...?