We have couple of EX4200s switches in Virtual Chassis mode running in the network. Each Virtual chassis has only 2 member switches.
We are required to upgrade the Junos OS on each member switch in the virtual chassis.
There are two approaches to perform Junos OS upgrade.
1) Perform the Junos OS upgrade on all members of the virtual chassis at the same time. This will be bring complete outage for period of time till all member switches come back after reboot.
2) Perform Junos OS upgrade on each member switch individually instead of whole virtual chassis. This however will avoid complete service outage.
Which option is considered to be the best practice / recommended approach that has a high probability of success and less prone to instabilities / abnormal behavior post upgrade situation.
If some one could help on this , would highly appreciate that.