If you are like me, you probably don't log into your system every day and run yum update to check for updates to apply. There is an easy way to keep up to date, though, using yum-cron. yum-cron allows you to configure your system to periodically check for updates and automatically apply them.
Using yum-cron in Centos 7, you also have the flexibility to specify what level of upgrades you want applied, eg: all updates, security updates, minimal security updates, etc. For stability on your production servers you'll probably only want to go with security updates, but on dev servers where it's not as much of an issue just go with all.
yum -y install yum-cron and then edit the file
/etc/yum/yum-cron.conf to set your options. Some of the options you'll want to change (the file is well commented to indicate what the options available are):
update_cmd = security download_updates = yes apply_updates = yes
Don't forget to make sure it's started and running:
systemctl restart yum-cron systemctl status yum-cron
There's a good description of how to get going with yum-cron at linuxaria with more details on the configuration options available.