{ "topology_description": { "type": "ReplicaSetNoPrimary", "servers": [ { "address": "a:27017", "type": "Unknown" }, { "address": "b:27017", "type": "Unknown" } ] }, "read_preference": { "mode": "Nearest", "maxStalenessSeconds": 90 }, "suitable_servers": [], "in_latency_window": [] }