Sitecore regularly provides new releases for
Sitecore Commerce and Upgrade Guides. As far as I can see, if you need to upgrade
XC 9 Initial Release to the latest version, you need to upgrade
Commerce Engine and Sitecore from version to version.
You can't skip migration to Update-2 (for example) if you want to migrate to Update-3. Of course, it will take a lot of time to upgrade environments and will affect the project budget.
I think, that instead of upgrading step by step, it is better to choose another way and setup latest version from scratch and migrate content and possibly analytics data. Сontent migration will be the most time consuming, yet relatively simple. After that, you can just switch production to new servers.
My question is:
What is the best way to upgrade Sitecore Commerce to the latest version, in your opinion?
Are there any license limitations to run 2 Commerce instances simultaneously during an upgrade? Is there support for Commerce xDB data migration available in xDB migration Tool?