"Warning: Permanently added ECDSA host key for IP address 'XXX.XXX.XXX.XXX' to the list of known hosts." in the error log

It is the message that sytstem added the certificate of IP address XXX.XXX.XXX.XXX in the known_host file(SSH server certificate list) , when there is a node connected for the first time or when the certificate of the host which had previously connected has been changed. This is a normal operation, and it does not affect the calculation result and can be ignored.