While I check this xtrabackup blog section I see it uses --user and --password along with --prepare, because I this I was always thinking that --prepare is something needs user/password and backed up database to be running. But While I check other resources in the internet (like this) they don’t use username/password. So does --prepare really needs to be done on source side, with username/password and access to backedup mysql if we gonna use backup for mysql replication setup?
Thanks for your question. --prepare is done totally offline and --user/–password are not required. I will ask the documentation team to fix the link you mentioned.