https://www.juniper.net/documentation/us/en/software/junos/virtual-chassis/topics/concept/virtual-chassis-software-automatic-update.html
Understanding Automatic Software Update on Virtual Chassis Member Switches | Junos OS | Juniper...
You can use the automatic software update feature to automatically update the Juniper Networks Junos operating system (Junos OS) version on prospective member...
automatic software update