--ssl-ca: The path name of the Certificate Authority (CA) certificate file. (--ssl-capath is similar but specifies the path name of a directory of CA certificate files.)

--ssl-cert: The path name of the server public key certificate file. This certificate can be sent to the client and authenticated against the CA certificate that it has.

--ssl-key: The path name of the server private key file.

To name the slave certificate and key files using an option file, add the following lines to the [client] section of the slave's my.cnf file, changing the file names as necessary:

[client]
ssl-ca=cacert.pem
ssl-cert=client-cert.pem
ssl-key=client-key.pem

Restart the slave server, using the --skip-slave-start option to prevent the slave from connecting to the master. Use CHANGE MASTER TO to specify the master configuration, and add the MASTER_SSL option to connect using encryption:

mysql> CHANGE MASTER TO
    -> MASTER_HOST='master_hostname',
    -> MASTER_USER='repl',
    -> MASTER_PASSWORD='password',
    -> MASTER_SSL=1;

Setting MASTER_SSL=1 for a replication connection and then setting no further MASTER_SSL_xxx options corresponds to setting --ssl-mode=REQUIRED for the client, as described in Command Options for Encrypted Connections. With MASTER_SSL=1, the connection attempt only succeeds if an encrypted connection can be established. A replication connection does not fall back to an unencrypted connection, so there is no setting corresponding to the --ssl-mode=PREFERRED setting for replication. If MASTER_SSL=0 is set, this corresponds to --ssl-mode=DISABLED.

To name the slave certificate and SSL private key files using the CHANGE MASTER TO statement, if you did not do this in the slave's my.cnf file, add the appropriate MASTER_SSL_xxx options:

    -> MASTER_SSL_CA = 'ca_file_name',
    -> MASTER_SSL_CAPATH = 'ca_directory_name',
    -> MASTER_SSL_CERT = 'cert_file_name',
    -> MASTER_SSL_KEY = 'key_file_name',

These options correspond to the --ssl-xxx options with the same names, as described in Command Options for Encrypted Connections. For these options to take effect, MASTER_SSL=1 must also be set. For a replication connection, specifying a value for either of MASTER_SSL_CA or MASTER_SSL_CAPATH, or specifying these options in the slave's my.cnf file, corresponds to setting --ssl-mode=VERIFY_CA. The connection attempt only succeeds if a valid matching Certificate Authority (CA) certificate is found using the specified information.

To activate host name identity verification, add the MASTER_SSL_VERIFY_SERVER_CERT option:

    -> MASTER_SSL_VERIFY_SERVER_CERT=1,

This option corresponds to the --ssl-verify-server-cert option, which was deprecated from MySQL 5.7 and removed in MySQL 8.0. For a replication connection, specifying MASTER_SSL_VERIFY_SERVER_CERT=1 corresponds to setting --ssl-mode=VERIFY_IDENTITY, as described in Command Options for Encrypted Connections. For this option to take effect, MASTER_SSL=1 must also be set. Host name identity verification does not work with self-signed certificates.

To activate certificate revocation list (CRL) checks, add the MASTER_SSL_CRL or MASTER_SSL_CRLPATH option:

    -> MASTER_SSL_CRL = 'crl_file_name',
    -> MASTER_SSL_CRLPATH = 'crl_directory_name',

These options correspond to the --ssl-xxx options with the same names, as described in Command Options for Encrypted Connections. If they are not specified, no CRL checking takes place.

To specify lists of ciphers and encryption protocols permitted by the slave for the replication connection, add the MASTER_SSL_CIPHER and MASTER_TLS_VERSION options:

    -> MASTER_SSL_CIPHER = 'cipher_list',
    -> MASTER_TLS_VERSION = 'protocol_list',

The MASTER_SSL_CIPHER option specifies the list of ciphers permitted by the slave for the replication connection, with one or more cipher names separated by colons. The MASTER_TLS_VERSION option specifies the encryption protocols permitted by the slave for the replication connection. The format is like that for the tls_version system variable, with one or more protocol names separated by commas. The protocols and ciphers that you can use in these lists depend on the SSL library used to compile MySQL. For information about the formats and permitted values, see Section 6.3.5, “Encrypted Connection Protocols and Ciphers”.

After the master information has been updated, start the slave replication process:

mysql> START SLAVE;

You can use the SHOW SLAVE STATUS statement to confirm that an encrypted connection was established successfully.

Requiring encrypted connections on the slave does not ensure that the master requires encrypted connections from slaves. If you want to ensure that the master only accepts replication slaves that connect using encrypted connections, create a replication user account on the master using the REQUIRE SSL option, then grant that user the REPLICATION SLAVE privilege. For example:

mysql> CREATE USER 'repl'@'%.example.com' IDENTIFIED BY 'password'
    -> REQUIRE SSL;
mysql> GRANT REPLICATION SLAVE ON *.*
    -> TO 'repl'@'%.example.com';

If you have an existing replication user account on the master, you can add REQUIRE SSL to it with this statement:

mysql> ALTER USER 'repl'@'%.example.com' REQUIRE SSL;