Hi @Sandeep K. ,
There is rolling update feature introduced on 17th may in upgrade 144 as per below link:
Post upgradation to this version , you should not face service interruption during Cluster upgrade.
Full upgrade goes with temporary downtime. Upgrade to version 148 is the first one that could have rolling upgrade - meaning only one node at the same time. This means zero downtime then. The mode of upgrade is controlled by Mission Control team and will be run when feasible. Cluster administrator will be notified accordingly what is the upgrade mode.