Updating Operating Systems | Upgrading Clusters

Purpose

Updating the operating system (OS) on a host, by either upgrading across major releases or updating the system software for a minor release, can impact the OpenShift Origin software running on those machines. In particular, these updates can affect the iptables rules or ovs flows that OpenShift Origin requires to operate.

Updating the Operating System on a Host

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

Update 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 Origin 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 Origin iptables topic. The ovs flow rules do not need to be saved, but restarting the OpenShift Origin node software will fix the flow rules.

Configure the host to be schedulable again:

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