Dump replication status before performing a master switch.

[peppla]

This information can be useful to debug changes and to recover if a failover is not properly executed.

[jemuhe]

Testing the script, before stop replication node in cluster one (cluster two is the replica).
All ok.
mysql -u root -p -D percona -e 'CALL replication_managerng(1)'
mysql: [Warning] Using a password on the command line interface can be insecure.
+---------------------+-------+-------------------------------+
| time | level | message |
+---------------------+-------+-------------------------------+
| 2022-08-30 10:43:37 | LOG | Node reported wsrep_ready: ON |
+---------------------+-------+-------------------------------+
+---------------------+-------+----------------------------------------------------------------------------------------------+
| time | level | message |
+---------------------+-------+----------------------------------------------------------------------------------------------+
| 2022-08-30 10:43:37 | LOG | Replication channel: test, node_name: ofzlt-dbp321, cluster_name: pxc-test-2, i_am_source: 0 |
+---------------------+-------+----------------------------------------------------------------------------------------------+
+---------------------+-------+-----------------------------------------------------------------------------------------------+
| time | level | message |
+---------------------+-------+-----------------------------------------------------------------------------------------------+
| 2022-08-30 10:43:37 | LOG | Replication channel: test, node_name: ofzlt-dbp321, cluster_name: pxc-test-2, i_am_replica: 1 |
+---------------------+-------+-----------------------------------------------------------------------------------------------+
+---------------------+-------+----------------------------------------------------------------------------------------------+
| time | level | message |
+---------------------+-------+----------------------------------------------------------------------------------------------+
| 2022-08-30 10:43:37 | LOG | Replication channel: test, node_name: ofzlt-dbp321, cluster_name: pxc-test-2, my_priority: 1 |
+---------------------+-------+----------------------------------------------------------------------------------------------+
+---------------------+-------+----------------------------------------+
| time | level | message |
+---------------------+-------+----------------------------------------+
| 2022-08-30 10:43:37 | LOG | Replication is running. We do nothing. |
+---------------------+-------+----------------------------------------+

After stop replication node in cluster one (cluster two is the replica) and executing procedure again in replica node.
It tries to connect to other node in cluster one but gtid error.

mysql> show slave status\G
*************************** 1. row ***************************
Slave_IO_State:
Master_Host: ofzlt-dbp312
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File:
Read_Master_Log_Pos: 4
Relay_Log_File: ofzlt-dbp321-relay-bin-test.000001
Relay_Log_Pos: 4
Relay_Master_Log_File:
Slave_IO_Running: No
Slave_SQL_Running: Yes
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: 0
Relay_Log_Space: 154
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: 0
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno: 1236
Last_IO_Error: Got fatal error 1236 from master when reading data from binary log: 'The slave is connecting using CHANGE MASTER TO MASTER_AUTO_POSITION = 1, but the master has purged binary logs containing GTIDs that the slave requires. Replicate the missing transactions from elsewhere, or provision a new slave from backup. Consider increasing the master's binary log expiration period. The GTID set sent by the slave is '6ae5824f-d886-ee12-5f10-891420371c5e:1-13,
73017ed8-d88e-ee12-7b6b-50ca722352a0:11-26', and the missing transactions are '73017ed8-d88e-ee12-7b6b-50ca722352a0:1-7'.'
Last_SQL_Errno: 0
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id: 1
Master_UUID: c7462f3c-2771-11ed-b6b6-000d3a3c10e1
Master_Info_File: mysql.slave_master_info
SQL_Delay: 0
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
Master_Retry_Count: 86400
Master_Bind:
Last_IO_Error_Timestamp: 220830 11:59:07
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set: 6ae5824f-d886-ee12-5f10-891420371c5e:1-13,
73017ed8-d88e-ee12-7b6b-50ca722352a0:11-26
Auto_Position: 1
Replicate_Rewrite_DB:
Channel_Name: test
Master_TLS_Version:
1 row in set (0.00 sec)

[peppla]

Are all the nodes running with "log_slave_updates" enabled. Otherwise the binlogs are not present on all the nodes.