Set Automatic Update on Amazon EC2

First install yum-cron using the command below:

sudo yum install yum-cron

Inside /etc/yum/yum-cron.conf
# Whether updates should be downloaded when they are available.
download_updates = yes

# Whether updates should be applied when they are available.  Note
# that download_updates must also be yes for the update to be applied.
apply_updates = yes

Enable and start:
sudo systemctl start yum-cron.service

sudo systemctl enable yum-cron.service