8.7. Adding more RHEL compute machines to your cluster

You can add more compute machines that use Red Hat Enterprise Linux (RHEL) as the operating system to an OpenShift Container Platform 4.5 cluster.

Prerequisites

Your OpenShift Container Platform cluster already contains RHEL compute nodes.
The hosts file that you used to add the first RHEL compute machines to your cluster is on the machine that you use the run the playbook.
The machine that you run the playbook on must be able to access all of the RHEL hosts. You can use any method that your company allows, including a bastion with an SSH proxy or a VPN.
The kubeconfig file for the cluster and the installation program that you used to install the cluster are on the machine that you use the run the playbook.
You must prepare the RHEL hosts for installation.
Configure a user on the machine that you run the playbook on that has SSH access to all of the RHEL hosts.
If you use SSH key-based authentication, you must manage the key with an SSH agent.
Install the OpenShift CLI (oc) on the machine that you run the playbook on.

Procedure

Open the Ansible inventory file at /<path>/inventory/hosts that defines your compute machine hosts and required variables.
Rename the [new_workers] section of the file to [workers].
Add a [new_workers] section to the file and define the fully-qualified domain names for each new host. The file resembles the following example:
```
[all:vars]
ansible_user=root
#ansible_become=True

openshift_kubeconfig_path="~/.kube/config"

[workers]
mycluster-rhel7-0.example.com
mycluster-rhel7-1.example.com

[new_workers]
mycluster-rhel7-2.example.com
mycluster-rhel7-3.example.com
```
In this example, the mycluster-rhel7-0.example.com and mycluster-rhel7-1.example.com machines are in the cluster and you add the mycluster-rhel7-2.example.com and mycluster-rhel7-3.example.com machines.
Navigate to the Ansible playbook directory:
```
$ cd /usr/share/ansible/openshift-ansible
```
Run the scaleup playbook:
```
$ ansible-playbook -i /<path>/inventory/hosts playbooks/scaleup.yml 1
```
1
For <path>, specify the path to the Ansible inventory file that you created.