We do not install it . Its an external layer and well documented. If its a local server you need to make sure its installed before running the script to install Gluu. https://docs.openebs.io/docs/next/installation.html
for example if you follow the rke guide we have we link to installing openebs on step number 6.
https://www.gluu.org/docs/gluu-server/4.2/tutorials/install-rancher/