Hi,
Here are a few tools available that could perform this.
- Junos Space (http://www.juniper.net/techpubs/en_US/junos-space15.2/platform/topics/concept/junos-space-deviceimagesscripts-overview.html)
- Ansible (http://www.juniper.net/techpubs/en_US/junos-ansible1.0/topics/example/junos-ansible-playbooks-device-os-installing.html)
- PyEz (http://junos-pyez.readthedocs.io/en/latest/jnpr.junos.utils.html#module-jnpr.junos.utils.sw)
Of course, it all depends greatly on what you would feel comfortable doing this with etc.
I recently did an upgrade of 100+ EX-4300's VC's (approx 600 members in total) using Ansible 2.0 and this included pre-checks, upgrade and post-checks, and ran in just under an hour.
Regards,
Andy