Users may find that attempting to upgrade an EX Virtual-Chassis (VC) by using the Junos Upgrade feature results in upgrade failure.
This article provides the reason for the error, and also a workaround.
In Sky Enterprise, the Junos Upgrade feature allows you to select the Junos OS image that you want to upgrade to from a pull-down menu. However, when attempting this, the upgrade fails.
When viewing the logs for the upgrade on this device, it reveals the following messages:
Logs
2020-06-25 09:52could not establish connection to jtac-EX3400-48P-r010-jtaclab: dial tcp 10.1.1.6:61083: connect: connection refused
2020-06-25 09:52connection establish to jtac-EX3400-48P-r010-jtaclab
2020-06-25 09:53system cleanup completed successfully
2020-06-25 10:06file successfully copied to device
2020-06-25 10:06md5 matched
2020-06-25 10:06JunOS install requested started
Checking pending install on fpc1
Checking pending install on fpc0
No copy is set, so skipping image push
fpc1:
/usr/libexec/ui/package: /var/tmp/junos-arm-32-20.1R1-S1.tgz: no such file
ERROR: No packages added
2020-06-25 10:07copy complete
The upgrade fails because the feature did not accommodate upgrading an EX Virtual-Chassis.
By default, the Junos Upgrade feature applies the no-copy option during the software upgrade. As a result, the Junos OS image does not get copied to the other members of the VC. This is indicated by the "No copy is set, so skipping image push" message.
As a workaround, on the Junos Upgrade tab, select the upgrade method as "Stage" as shown in the screenshot below:

This will do a secure file copy (scp) to the master VC's /var/tmp
directory.
After this is completed, upgrade from the Junos Command Line Interface (CLI) by issuing a request system software add
. This will automatically upgrade the master VC, along with the other members of the VC.