Why mongodb never end some connection My mongod runs out of connections from time to time. But when I restart the instance, it becomes normal.

I check the log and found some connections were created and never be ended. This cause the connection depleted quickly.

My mongo cluster consists of  of 3 shards, each with 3 replicasets. So there are 9 mongod instance and 5 mongos instance. The problem occurs in one of the mongod instance.

I am running mongo version 2.4.

Here is part of the log:

Tue Sep  1 23:24:09.245 [initandlisten] connection accepted from 10.1.1.2:35569 #987213 (291 connections now open)
Tue Sep  1 23:24:09.687 [conn987214] end connection 10.1.1.1:36381 (339 connections now open)
Find out how many connections are there to the database vs how many available.  This command in Mongo Shell will tell you exactly that:

db.serverStatus().connections