'Adding existing VMs into OpenShift cluster

I have a fleet of "reserved" AWS VMs that I want to add to my OpenShift cluster. I am able to extend the cluster via autoscaler allocating new VMs, but is it possible to add the existing reserved VMs to the cluster?

I want them to run CoreOS and not RHEL. The cluster runs on RedHat Opeshift 4.8

thanks!

openshift

Solution 1:^[1]

Yes this is possible as far as I know. Basically you'll need to do the following:

Generate the Ignition file (oc get $(oc get secret -n openshift-machine-api -o name | grep worker) -n openshift-machine-api -o yaml | grep userData | awk ‘{print $2}’ | base64 -d > worker.ign) and make it available via HTTP somewhere.
Start your VMs with the CoreOS AMI (see your existing machines for which exact one)
For the startup, set the kernel parameters (coreos.inst.install_dev, coreos.inst.ignition_url)
Once the VM is started, approve the CSR ( oc get csr, oc adm certificate approve)

You can find the commands with some more details in some blog posts here:

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'Adding existing VMs into OpenShift cluster

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