Please check the updated article here: https://www.nomachine.com/AR10K00710.
To install Xvfb on Amazon EC2 Red Hat t2.micro you should enable rhui-REGION-rhel-server-optional repository by running:
$ sudo subscription-manager repos –enable rhui-REGION-rhel-server-optional
or set it manually in /etc/yum.repos.d/redhat-rhui.repo
Amazon EC2 Red Hat t2.micro you should enable