Using Centos 7x64 image, "hostnamectl set-hostname example.com" should preserve after reboots. Log was showing that hostname was reset after reboot to "vultr.guest" by systemd-hostnamed. After an hour of researching the problem, found that /etc/cloud/cloud.cfg doesn't have "preserve_hostname: true" by default. Adding this config option solved the problem. Is this option omitted intentionally?