Currently Vault is running with Shamir seal. I was able to migrate the seal to AWS KMS in a testing setup but have no idea how to create recovery keys and docs are not very helpful either.
Even upgrading to 1.3.2 which should use new-style Shamir secret after rekeying, still can’t generate recovery keys (it says not supported).
I believe your existing unseal keys will become recovery keys when you convert to auto-unseal using AWS KMS keys. They will then revert back to unseal keys if you ever turn off auto-unseal later.
I also didn’t find this clear in the documentation at first, but I can confirm this is how it works with GCP auto-unseal, and presumably AWS KMS auto-unseal should be the same.
There does not appear to be any separate mechanism to create recovery keys directly that I could find. They’re just the unseal keys from before the migration to auto-unseal.