Adding Nodes to an Agent-based Cluster

Use a customized Red Hat Enterprise Linux CoreOS (RHCOS) ISO image to add worker nodes to an OpenShift cluster that was created with the Agent-based Installer.

Access the cluster by using the oc command as a user who can read Machine Config Operator secrets.
Install coreos-installer on the system used to create the ISO image.
Provide a web server that new nodes can access to download the worker Ignition configuration.
Identify the target installation device for each new node. This procedure uses /dev/sda as an example.
Have a pull secret available for registry authentication.

This procedure creates a Day 2 ISO image, customizes its kernel arguments, and uses the image to provision a new worker node. The node downloads its Ignition configuration from the specified web server during installation.

Note

Use HTTP delivery of the Ignition configuration only in a controlled environment. Ensure that network security rules allow new nodes to access the web server.

On the system used to create the ISO image, create a working directory and set the registry authentication file.
```
export REGISTRY_AUTH_FILE=/home/opc/PullSecret.json
export DIR=day2
mkdir -p $DIR
cd $DIR
```

Export the worker Ignition configuration from the cluster.

oc -n openshift-machine-config-operator get secret worker-user-data \
-o jsonpath='{.data.userData}' | base64 -d > worker.ign

Copy the worker Ignition configuration to a web-server directory that the new node can access.

sudo mkdir -p /var/www/html/day2
sudo cp worker.ign /var/www/html/day2/worker.ign
sudo chmod 0644 /var/www/html/day2/worker.ign

Verify that the web server can provide the Ignition configuration and that the configuration is valid JSON.

curl -sS http://webserver/day2/worker.ign | head -n 2
curl -sS http://webserver/day2/worker.ign | jq -e . >/dev/null && echo OK

Create a Day 2 ISO image. Specify the MAC address and target installation device for the new node.
```
oc adm node-image create \
--mac-address=00:00:00:00:00:00 \
--root-device-hint=deviceName:/dev/sda
```
The command creates the node.x86_64.iso file. Use the actual MAC address when creating an ISO image for a specific host.

Customize the ISO image with the console, debugging, live-environment, installation-device, and Ignition URL kernel arguments.

coreos-installer iso customize -f \
--live-karg-append console=tty0 \
--live-karg-append console=ttyS0,115200n8 \
--live-karg-append rd.debug \
--live-karg-append rd.live.ram=1 \
--live-karg-append rd.live.overlay=none \
--live-karg-append rd.luks=0 \
--live-karg-append rd.lvm=0 \
--live-karg-append rd.md=0 \
--live-karg-append rd.dm=0 \
--live-karg-append coreos.liveiso.fromram \
--live-karg-append coreos.inst.install_dev=/dev/sda \
--live-karg-append coreos.inst.ignition_url=http://webserver/day2/worker.ign \
-o rhcos-auto-worker-oci-ram-debug-DAY2-1.iso \
node.x86_64.iso

Note

Replace /dev/sda and http://webserver/day2/worker.ign with values for the new node and your environment.

Verify the kernel arguments embedded in the customized ISO image.

coreos-installer iso kargs show rhcos-auto-worker-oci-ram-debug-DAY2-1.iso

Upload the customized ISO image to Object Storage, create an OCI custom image, and create a worker instance that uses the custom image.
For the OCI image upload, custom image, and image capability steps, see Creating the OpenShift Discovery ISO Image. For instructions about creating an instance, see Creating an Instance.
On the new node, verify the kernel arguments and installation logs.
```
cat /proc/cmdline
journalctl -b -u coreos-installer -u ignition-*
```
From the cluster, monitor the node provisioning and join process.
```
oc adm node-image monitor --ip-addresses <node_IP_address>
```
Use the output to identify whether the node is blocked during Ignition retrieval, kubelet startup, certificate signing request approval, or readiness.

Oracle Cloud Infrastructure Documentation

Adding Nodes to an Agent-based Cluster