Aruba IAP upgrades

I have a simple question that I can’t find online. I found the Aruba how to upgrade IAP with out airwave guide but it doesn’t state what happens to the cluster when I hit upgrade now.

Here what I think I should do.

1. I log into the master VC AP.
2. Backup configuration / certs
3. go to maintenance > firmware > upgrade now Does this upgrade now button only do the current AP or the whole cluster. I would hate to log in 10 times to upgrade APs. Then would the VC only upgrade one at a time or does every AP at that moment. I know airwave has some slow roll out feature to limit WiFi downtime. I don’t know if the IAP do the same thing.