@MichaelCropper, thank you for the additional details. I followed everything up to mounting the CDrom. Instead I chose to follow the instructions here instead: https://gitlab.com/xen-project/xen-guest-agent/-/releases

BTW... removing the old package may leave some residual config files behind. It should be safe to add --purge to the apt remove command. If not, you may need to do it using dpkg later. I listed all the packages with residual config using:

sudo dpkg -l | grep "^rc" | tr -s ' ' | cut -d ' ' -f 2

...and once I was sure of doing so for all packages, I followed with:

sudo dpkg --purge $(COLUMNS=200 dpkg -l | grep "^rc" | tr -s ' ' | cut -d ' ' -f 2)

If there is a downside to using the gitlab package rather than the tools on the CDrom, I'm hoping someone will let me know!

@bvitnik Thank you -- very useful information!

We have a small, two-host pool, having just added a new host. The master is a Dell R640 (Intel(R) Xeon(R) Gold 6150 CPU @ 2.70GHzIntel(R) Xeon(R) Gold 6150 CPU @ 2.70GHz) and the second, an R630 (Intel(R) Xeon(R) CPU E5-2650 v3 @ 2.30GHz). I attempted to migrate a VM to the second host as a test and received the error:

"code": "VM_INCOMPATIBLE_WITH_THIS_HOST",
  "params": [
    "OpaqueRef:<UUID1>",
    "OpaqueRef:<UUID2>",
    "VM last booted on a CPU with features this host's CPU does not have."
  ],...

I don't see much other detail that seems to offer clues. How do I determine what the incompatibility actually is? If the incompatibility is determined, is there some means of disabling features to ensure capatibility?

I did try a different VM and the migration worked!?