I’ve recently been looking into this myself migrating from Rancher 1.6 and found that the etc data is persisted to /var/lib/rancher on disk.
In the single node example there’s a section on persisting this data at the following link:
I currently have this as an external volume so that I can create new hosts and mount the disk to retain this information. I’m also backing this up regularly to S3 as a tar archive using the method detailed in the following link: