Operating System Updates and Upgrades - Upgrading a Cluster | Installation and Configuration

Updating and Upgrading the Operating System

Updating or upgrading your operating system (OS), by either changing OS versions or updating the system software, can impact the OpenShift Container Platform software running on those machines. In particular, these updates can affect the iptables rules or ovs flows that OpenShift Container Platform requires to operate.

Use the following to safely upgrade the OS on a host:

Ensure the host is unschedulable, meaning that no new pods will be placed onto the host:
```
$ oc adm manage-node <node_name> --schedulable=false
```

Migrate the pods from the host:

$ oc adm drain <node_name> --force --delete-local-data --ignore-daemonsets

Install or update the *-excluder packages on each host with the following. This ensures the hosts stay on the correct versions of OpenShift Container Platform, as per the atomic-openshift and docker packages, instead of the most current versions:
```
# yum install atomic-openshift-excluder atomic-openshift-docker-excluder
```
This adds entries to the exclude directive in the host’s /etc/yum.conf file.
Update or upgrade the host packages, and reboot the host. A reboot ensures that the host is running the newest versions, and means that the docker and OpenShift Container Platform processes have been restarted, which will force them to check that all of the rules in other services are correct.

However, instead of rebooting a node host, you can restart the services that are affected, or preserve the iptables state. Both processes are described in the OpenShift Container Platform IPtables topic. The ovs flow rules do not need to be saved, but restarting the OpenShift Container Platform node software will fix the flow rules.

Configure the host to be schedulable again:

$ oc adm manage-node <node_name> --schedulable=true