Migrate all hosts from old foreman stack to new

Foreman and Proxy versions:
3.6 /4.8

Would just like to know best approach for migrating x number of content hosts from one foreman stack (CentOS7 v 3.2) to our newer stack (eL8 v3.8)
Can I clean /refresh the subscription on them all then rejoin to new or will i need to delete via GUI?

Thanks,

The process of migrating from one Foreman stack to another depends very much on which features you are using.
But to just answer your explicit question: If your only concern is switching where hostsconsume the repositories from a new stack, unregistering a host via subscription-manager and then registering it to the new system should be enough as far as I know.

Well, you still need to find a way to get the same repository set as on the old katello server. When I migrated to el8 there wasn’t a way to do this from the katello end, thus I ended up making sure that all product and repository labels on the new server are identical, then I have dumped the current enabled repositories on all clients via remote execution using dnf repolist, switched to the new server and reenabled all repositories from the list.

the new EL8 stack that I’ve setup is identical, incuding products, to the exisiting. I’ve run a test against one host - unregistered it, removed old ca rpm, then registered to new (using new ca) and subscribed. Then just removed from old in GUI. All seemed ok.

Might not need to remove from old GUI given we will be powering it all off when the hosts have re-registered, otherwise a bulk hammer command would have been my go-to