To set up a new Cluster node, you should follow these steps:

Network it

Do the standard steps to add new entries for a node (or block of nodes) to DHCP and DNS.

Also make sure the switches/routers/cables are set up right.

Install Ubuntu

The preferred method is to use Netboot, but a regular Ubuntu install stick works as well. If installing from an USB stick make sure your hostname matches the one specified in DNS/DHCP.

Install SSH Server

apt install openssh-server. 'Nuf said.

Run the Ansible play

First, make sure you add the node to an existing/new host group that has the cluster role. Then, you can just run ansible-playbook, sit back, kick your feet up, and wait for the install to finish.