How can I tell if a specific Mongo instance has active connections?

Question

I'm upgrading a sharded cluster and want to turn one of three mongos instance off. I've guaranteed that new incoming connections will not take place because I disabled the box in my load balancer. However, I'm concerned there might be existing connections on the mongos instance still active.

I've run the following on the Mongo instance:

db._adminCommand("connPoolStats");

Do you have any tis on interpreting the result? Is this the correct command?

Answer 1

The cursorInfo command should work. If there are no more cursors, then it's ok to shut off the mongos. Any connections that still exist will simply fail over to another mongos through the load balancer when they try to reconnect (assuming they have an appropriate reconnection policy in place). The only thing you need to worry about is cursors, since they have state, which is taken care of by cursorInfo.