Why is my private IP missing from my CentOS 7 server?

When restarting a CentOS 7 server after adding it to a private network, the configuration of the new private network interface might fail, leaving it without an IP address. This can be fixed by retrying after applying a small change to cloud-init:

# Patch cloud-init
sudo sed "s/== 'static'/in ['static', 'static6']/" -i /usr/lib/python2.7/site-packages/cloudinit/net/sysconfig.py

# Reset cloud-init
sudo cloud-init clean

# Reboot to apply
sudo reboot

This is only necessary if you are just doing a reboot. The IP configuration should always succeed after a reinstall. Other operating systems are also unaffected.