RE: http://docs.mongodb.org/manual/tutorial/deploy-config-servers/#deploy-three-config-servers-for-production-deployments

This is a really great guide to expanding from one config server to three config servers for the purposes of deploying an existing system into production. It mentions the use of the existing command-line for the config servers, but omits the necessary command-line change of all mongos to include all three config servers - if they are restarted as the instructions say, then the cluster will continue to use just one config server. I believe this should be covered in step 4.