Automation

I'm wondering what's the experience of the community with JunOS upgrades with Apstra.

Is there any intelligence to handle correct upgrade paths?, going from 17.3R3 to 21.3R3 for example?.

From the initial documentation review, it seems it supports very specific "previous" and "next" versions combination.

Gonna take a deep breathe and try to be concise with this.. 

For Junos OS upgrades, you want to look in the specific release notes. Near the bottom, you will find a section called Upgrade and Downgrade Support Policy for Junos OS Releases that states one can "upgrade to the next three subsequent releases or downgrade to the previous three releases". 

In the lab, I have done greater jumps than that, allegedly... 

When I have been involved in production upgrades, we have done step upgrades where we line up the upgrades back-to back and follow Juniper guidance as to what the biggest jump should be. For example, two specific, strategic, and tested upgrades in the same maintenance window across a network in order to jump more than 3 subsequent releases. 

KB on Junos Software Versions

Now with Apstra, I don't have personal experience, but I do know that we recommend Apstra perform the upgrade.