27019 MongoDB-config TCP
Reference for TCP port 27019, commonly associated with MongoDB-config.
What it's for
Port 27019 is the conventional port for MongoDB config servers — the components in a sharded cluster that store metadata about which data lives on which shard, cluster configuration, and chunk distribution. mongos router processes consult the config servers to know how to route each incoming query to the correct shard(s).
Protocol basics
Config servers speak the same BSON-based MongoDB wire protocol as the rest of the cluster, just handling metadata rather than application data itself. Because config servers are essential to the cluster's ability to correctly route queries, they're typically deployed as their own small replica set for redundancy — losing config server availability doesn't destroy application data, but it can prevent the cluster from correctly routing new queries until it's restored. Like shard servers, config servers should be reachable only by the cluster's internal components, never exposed externally.