When I want to move a single mongodb server into a sharded cluster, I know that I need 3 config servers. Since we have evertything on one single EXSi server I just want to ask if it is the preferred way is really to setup 3 small config server VM's and two additional VM's for the mongod servers. Does this make sense since the the OS on the config server alone will consume 300MB ram (or so)? Is it a good idea to use one VM and three docker containers for the config servers instead? And should I install the mongos router(s) on the two data nodes or on the server where the config servers are living? Let me sum up the question how many VM's do I realy need as a minimum for a sharded mongo cluster?
Or is Ubuntu Snappy Core an option?