I designed a method of move follow.
“User A @ Instance A” has a digital signature mechanism similar to PGP, with the user having a private key.
Each instance associated with “User A” stores this digitally signed public key.
When you want to move account, use “User A @ instance A” digital signature private key to issue a move account of the certificate, and also contains a “User A” follow the list, upload to the “user B @ instance B” settings.
The instance of “User B” sends a “User A” digitally signed change request to each instance associated with “User A” based on the relationship list, and the other instances use the public key authentication information Signature to prove that I sent.
Even if “Instance X” is down, you can migrate the complete relationship as long as you have the private key and the relational list.