We have a pretty intensive process that stresses our mongod servers. When this process is running, we encounter the following issue: suddenly, there's a sudden increase in # of connections mongos opens, and then it starts taking more and more cpu until it becomes totally stuck. Please see the 2 graphs attached.

When this happens, mongos logs shows A LOT of open/close connection messages (to the mongod servers). This trigger for this process seems to be a chunk move. When the move is complete, the ChunkManager refreshes - and then the connections starts opening and closing endlessly.

Note that our mongod+mongos run on super strong machines, c4.4xlarge.

Is this known / any workaround?

SERVER-22611 (opened by myself) seems to be related, but fixed only in 3.4, we are using 3.2.12.