in a system with 3 config servers, i shut down one of them. i then did the following which returned an error. (1) the message isn't very clear i would really like to know that a config server was unreachable not a mongod for example. (2) arguably i shouldn't get an error at all the query could be retried to another server. however be careful retries could add latency if multiple down and/or have a multiplicative effect on load. also is there a background detector of heartbeat? that might help some as another approach.