To use NTP:
Install NTP on the machines that will host Eucalyptus components.
yum install ntp
Open the /etc/ntp.conf file and add NTP servers, if necessary, as in the following example.
server 0.pool.ntp.org server 1.pool.ntp.org server 2.pool.ntp.org
Save and close the file. Synchronize your server.
ntpdate -u YOUR_NTP_SERVER
Configure NTP to run at reboot.
systemctl enable ntpd.service
systemctl start ntpd.service
Synchronize your system clock, so that when your system is rebooted, it does not get out of sync.
Repeat on each host machine that will run a Eucalyptus service.