environment: host a (192.168.128.131) + host B (192.168.128.132)

Objective: to achieve MySQL database backup (AB replication) method

Problem Description:

MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
                Slave_IO_State: Connecting to master
                   Master_Host: 192.168.128.131
                   Master_User: userb
                   Master_Port: 3306
                 Connect_Retry: 60
               Master_Log_File: master1.000001
           Read_Master_Log_Pos: 950
                Relay_Log_File: localhost-relay-bin.000001
                 Relay_Log_Pos: 4
         Relay_Master_Log_File: master1.000001
              Slave_IO_Running: Connecting　　# An error has occurred and the IO thread is in a connected state
             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: 950
               Relay_Log_Space: 256
               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: 2003
                 Last_IO_Error: error connecting to master '[email protected]:3306' - retry-time: 60  maximum-retries: 86400  message: Can't connect to MySQL server on '192.168.128.131' (113 "No route to host")
                Last_SQL_Errno: 0
                Last_SQL_Error: 
   Replicate_Ignore_Server_Ids: 
              Master_Server_Id: 0
                Master_SSL_Crl: 
            Master_SSL_Crlpath: 
                    Using_Gtid: No
                   Gtid_IO_Pos: 
       Replicate_Do_Domain_Ids: 
   Replicate_Ignore_Domain_Ids: 
                 Parallel_Mode: conservative
                     SQL_Delay: 0
           SQL_Remaining_Delay: NULL
       Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
              Slave_DDL_Groups: 0
Slave_Non_Transactional_Groups: 0
    Slave_Transactional_Groups: 0

solution process:

According to last_ IO_ Error message: can’t connect to MySQL server on ‘192.168.128.131’ (113 “no route to host”) finds that host B can’t connect to host a, and then tries to Ping host a

[root@localhost ~]# ping 192.168.128.131
PING 192.168.128.131 (192.168.128.131) 56(84) bytes of data.
64 bytes from 192.168.128.131: icmp_seq=1 ttl=64 time=0.384 ms
64 bytes from 192.168.128.131: icmp_seq=2 ttl=64 time=0.267 ms
64 bytes from 192.168.128.131: icmp_seq=3 ttl=64 time=0.412 ms
64 bytes from 192.168.128.131: icmp_seq=4 ttl=64 time=0.245 ms
64 bytes from 192.168.128.131: icmp_seq=5 ttl=64 time=0.259 ms
^C
--- 192.168.128.131 ping statistics ---
5 packets transmitted, 5 received, 0% packet loss, time 4005ms
rtt min/avg/max/mdev = 0.245/0.313/0.412/0.071 ms

Host B can ping host A. It is speculated that it may be a problem with the firewall, so close the firewall

[root@localhost ~]# iptables -F　　# Turn off the firewall
[root@localhost ~]# setenforce 0　　# turn off SELinux

Re execute the slave configuration of B host again:

MariaDB [(none)]> stop slave;
Query OK, 0 rows affected (0.002 sec)

MariaDB [(none)]> change master to
    -> master_host='192.168.128.131',
    -> master_user='userb',
    -> master_password='root',
    -> master_log_file='master1.000001',
    -> master_log_pos=1845;
Query OK, 0 rows affected (0.005 sec)

MariaDB [(none)]> start slave;
Query OK, 0 rows affected (0.003 sec)

To view the slave status of host B:

MariaDB [(none)]> show slave status\G
*************************** 1. row ***************************
                Slave_IO_State: Waiting for master to send event
                   Master_Host: 192.168.128.131
                   Master_User: userb
                   Master_Port: 3306
                 Connect_Retry: 60
               Master_Log_File: master1.000001
           Read_Master_Log_Pos: 1845
                Relay_Log_File: localhost-relay-bin.000002
                 Relay_Log_Pos: 553
         Relay_Master_Log_File: master1.000001
              Slave_IO_Running: Yes
             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: 1845
               Relay_Log_Space: 866
               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: 0
                 Last_IO_Error: 
                Last_SQL_Errno: 0
                Last_SQL_Error: 
   Replicate_Ignore_Server_Ids: 
              Master_Server_Id: 131
                Master_SSL_Crl: 
            Master_SSL_Crlpath: 
                    Using_Gtid: No
                   Gtid_IO_Pos: 
       Replicate_Do_Domain_Ids: 
   Replicate_Ignore_Domain_Ids: 
                 Parallel_Mode: conservative
                     SQL_Delay: 0
           SQL_Remaining_Delay: NULL
       Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
              Slave_DDL_Groups: 0
Slave_Non_Transactional_Groups: 0
    Slave_Transactional_Groups: 2