This one in not very different than Topology refactoring using classic MySQL replication commands - version 1, actually it's the other way around.

Context:

• Initial state:

  dbfoo1(M) - dbfoo2(S)
            \ dbfoo3(S)

• Desired state:

  dbfoo1(M) - dbfoo2(MS) - dbrfoo3(S)

Let's get it done:

1. stop slave on dbfoo3

MariaDB [(none)]> stop slave;

2. check the "freezing point" on dbfoo2 and note down the output from 'show' commands

MariaDB [(none)]> stop slave; show master status\Gshow slave status\Gstart slave;

*************************** 1. row ***************************
            File: bin.009642
        Position: 91547140
    Binlog_Do_DB: 
Binlog_Ignore_DB: 
1 row in set (0.00 sec)

*************************** 1. row ***************************
               Slave_IO_State: 
                  Master_Host: dbfoo1
                  Master_User: user
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: bin.293567
          Read_Master_Log_Pos: 90061272
               Relay_Log_File: relay.028914
                Relay_Log_Pos: 90061553
        Relay_Master_Log_File: bin.293567
             Slave_IO_Running: No
            Slave_SQL_Running: No
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 90061272
              Relay_Log_Space: 90062173
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 270
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
                   Using_Gtid: No
                  Gtid_IO_Pos: 
1 row in set (0.00 sec)

Query OK, 0 rows affected (0.00 sec)

3. make sure dbfoo3 has the same data as dbfoo2 and use Relay_Master_Log_File and Exec_Master_Log_Pos from show master status

MariaDB [(none)]> start slave until master_log_file='bin.293567', master_log_pos=90061272;

4. point dbfoo3 to dbfoo2 and start the slave

MariaDB [(none)]> stop slave;
MariaDB [(none)]> change master to master_host='foo2', master_log_file='bin.009642', master_log_pos=91547140;
MariaDB [(none)]> start slave;

I assume you you have a high availability (master - slave topology) setup. I will be brief and technical on this one :)

Context:

• dbfoo1 is master and dbfoo2 is slave - dbfoo1(M) - dbfoo2(S)
• dbfoo2 has to be promoted to master - dbfoo2(M) - dbfoo1(S)
• note that in some cases the slave requires a innodb buffer pool warm-up before being promoted to master

Let's get to work:

• remove the VIP from dbfoo1 (/etc/network/interfaces)
• add the VIP to dbfoo2 (/etc/network/interfaces)
• take down the VIP on dbfoo1

[codesyntax lang="bash"]

dbfoo1# ip a d dev eth0 x.x.x.x/y

[/codesyntax]

• dbfoo2 should not be lagging behind dbfoo1

dbfoo2> show slave status\G
Relay_Log_Space: 0
Seconds_Behind_Master: 0

• check the "freezing point" on dbfoo1 and note down the output from 'show' commands (this is optional but good to have)

dbfoo1> flush logs;
dbfoo1> show master status\G
dbfoo1> show slave status\G

• check the "freezing point" on dbfoo1 and note down the output from 'show' commands

dbfoo2> slave stop;
dbfoo2> flush logs;
dbfoo2> show master status\G  <--- from here use File: and Position: to attach dbfoo1 (two steps below)
dbfoo2> show slave status\G

MariaDB [(none)]> show master status\Gshow slave status\G
*************************** 1. row ***************************
            File: bin.005662
        Position: 385
    Binlog_Do_DB: 
Binlog_Ignore_DB: 
1 row in set (0.00 sec)

*************************** 1. row ***************************
               Slave_IO_State: 
                  Master_Host: dbfoo1
                  Master_User: user
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: bin.006034
          Read_Master_Log_Pos: 245
               Relay_Log_File: relay.017538
                Relay_Log_Pos: 523
        Relay_Master_Log_File: bin.006034
             Slave_IO_Running: No
            Slave_SQL_Running: No
              Replicate_Do_DB: 
          Replicate_Ignore_DB: 
           Replicate_Do_Table: 
       Replicate_Ignore_Table: 
      Replicate_Wild_Do_Table: 
  Replicate_Wild_Ignore_Table: 
                   Last_Errno: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 245
              Relay_Log_Space: 1128
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: NULL
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 310
1 row in set (0.00 sec)

MariaDB [(none)]>

• finish the flip - promote dbfoo2 as master by adding the VIP on it

[codesyntax lang="bash"]

dbfoo2# ip a a dev eth0 x.x.x.x/y

[/codesyntax]

• connect dbfoo2  to the new master

dbfoo1> reset slave all;
dbfoo1> change master to master_host='dbfoo2', master_user='user', master_password='password', master_log_file='bin.005662', master_log_pos=385;
dbfoo1> slave start;

• done!