Network Manager is a fantastic utility for managing network connectivity on your server, though it's not for everyone. This utility comes installed by default with Ubuntu Server, but if you're using a cloud appliance (such as a VPS), it's most likely disabled, or maybe even removed. The reason for this is because even though this utility is very useful, it's not necessarily the best fit for every use-case.
Network Manager is a service (a.k.a. daemon) that runs in the background and manages your network connections. On a desktop Linux distribution, it does everything from managing connectivity to managing your wireless networks. With it, you can configure profiles, and create custom connections you can switch between.
On servers, the desktop-related features of Network Manager aren't all that useful, but the network connectivity management portion certainly is. With Network Manager, it keeps an eye on whether or not your server is connected to a network. It even...