After upgrading MongoDB from version 2.4 to 2.6, I am not able to connect to it from another machine. The firewall has been checked to ensure that port 27017 is opened for the machine that I want to connect from.

So what else could go wrong?  Well, I was impatient and turned to you know what… Google search. According to this link:!msg/mongodb-user/yhf05AW-hK8/YqES0cVIXlUJ, the problem is due to the database is bound to only local IP.

Indeed, this was the case, and I could have found it out very easily had I run the netstat command:

To fix this, modify /etc/mongod.conf to include your server’s IP. Make sure you use ‘;’ instead of ‘,’ to list IP addresses.

If you use Salt to manage your server, here is an example: