Review this information to understand rolling upgrade of Oracle Grid Infrastructure.

When you upgrade Oracle Grid Infrastructure, you upgrade the entire cluster. You cannot select or de-select individual nodes for upgrade. Oracle does not support attempting to add additional nodes to a cluster during a rolling upgrade. Oracle recommends that you leave Oracle RAC instances running when upgrading Oracle Clusterware. When you start the root script on each node, the database instances on that node are shut down and then the rootupgrade.sh script starts the instances again.

You can use root user automation to automate running the rootupgrade.sh script during the upgrade. When you use root automation, you can divide the nodes into groups, or batches, and start upgrades of these batches. Between batches, you can move services from nodes running the previous release to the upgraded nodes, so that services are not affected by the upgrade. Oracle recommends that you use root automation, and allow the rootupgrade.sh script to stop and start instances automatically. You can also continue to run root scripts manually.