I need to setup a 3x3 MongoDB 3.2 Cluster (3 Shards, 6 Replicas) and would like to keep the number of servers as small as possible. Can I run the config servers on the replica and shard servers (I thought about running 9 config server (1 config shard and 8 replica shard))? And is it a good idea or are there problems when one or the other server goes down?
SO Questions MongoDB shards and config servers on the same server? and Should I run MongoDB config and mongos on the same servers? mention that running config server on shards is not a good idea but is this still true for replicas even when using 9 config server?