Patches are applied to VMs in all zones at the same time.
Unspecified
Mode must be specified.
ZoneByZone
Patches are applied one zone at a time. The patch job begins in the
region with the lowest number of targeted VMs. Within the region,
patching begins in the zone with the lowest number of targeted VMs. If
multiple regions (or zones within a region) have the same number of
targeted VMs, a tie-breaker is achieved by sorting the regions or zones
in alphabetical order.
