There are two types of replication.

• Master-Master - Both databases are masters, meaning both can be used for reading and writing.
• Master-Slave - One database is the master, the other is the slave. Only the master can read and write, the slave can only read.

This assumes you have installed mySQL or MariaDB on two different Docker containers.

You will first need to define the log_bin directive in the main configuration file (e.g. /etc/mysql/mariadb.conf.d/50-server.cnf).

log_bin = /var/lib/mysql/binary-log

The data directory, which is /var/lib/mysql by default, should contain the binary log files.

-rw-rw----. 1 mysql mysql       325 May 27 07:49 binary-log.000001
-rw-rw----. 1 mysql mysql        29 May 27 07:49 binary-log.index

Each system will need to have a unique server ID in the main configuration file. For example, the master could have server id 1.

server-id = 1

And the slave could have server id 2.

server-id = 2

On the master system, create a user account that will be used for replication and grant the user the replication slave priviledge.

docker exec mariadb mysql -e "create user 'replication_user'@'%' identified by 'itsasecret'"
docker exec mariadb mysql -e "grant replication slave on *.* to 'replication_user'@'%'"

On the master, use the flush tables with read lock command to disable write access to tables. The tables will continue to have read access.

docker exec mariadb mysql -e "flush tables with read lock"

On the master, export the database that you want replicated.

~]# docker exec -it mariadb bash
root@fe53282f4be6:/# mysqldump -u username --databases database_name > db1.sql
root@fe53282f4be6:/# exit

Use the docker cp command to copy the .sql file from the container to the Docker system.

docker cp mariadb:/path/to/db1.sql /tmp/db1.sql

On the slave, use the docker cp command to copy the .sql file from the Docker system to the container.

docker cp /path/to/db1.sql mariadb:/tmp/db1.sql

On the slave, import the .sql file.

~]# docker exec -it mariadb bash
root@89f1f659b669:/# mysql -u username -p < db1.sql
root@89f1f659b669:/# exit

On the master, use the show master status command to get the name and position of the binary log file. Optionally, the reset master command can be used so that prior binary log files are removed and a new binary log file ending in 000001 is used.

~]# docker exec mariadb mysql -e "show master status \G"
            File: binary-log.000015
        Position: 725
    Binlog_Do_DB:
Binlog_Ignore_DB:

On the slave, stop the slave.

docker exec mariadb mysql -e "stop slave"

On the slave, issue the following command.

docker exec mariadb mysql -e "CHANGE MASTER TO
  MASTER_HOST='<master hostname>',
  MASTER_USER='replication_user',
  MASTER_PASSWORD='itsasecret',
  MASTER_PORT=3306,
  MASTER_LOG_FILE='<master binary file>',
  MASTER_LOG_POS=<master position>,
  MASTER_CONNECT_RETRY=10;"

On the slave, start the slave.

docker exec mariadb mysql -e "start slave"

On the slave, issue the show slave status command.

mysql -e "show slave status \G"

And something like this should be returned.

       Slave_IO_State: Waiting for master to send event
          Master_Host: master.example.com
          Master_User: replication_user
          Master_Port: 3306
        Connect_Retry: 10
      Master_Log_File: binary-log.000015
  Read_Master_Log_Pos: 725
       Relay_Log_File: mariadb-relay-bin.000002
        Relay_Log_Pos: 552
Relay_Master_Log_File: binary-log.000015
     Slave_IO_Running: Yes
    Slave_SQL_Running: Yes

On the master, release the tables lock, restoring write access to the tables.

docker exec mariadb mysql -e "unlock tables"

Let's say column001 in table001 in the db1 database 

[root@master ~] mysql -e "select column001 from db1.table001 where id = 123"
+---------------+
| column001     |
+---------------+
| foo           |
+---------------+

[root@slave ~] mysql -e "select column001 from db1.table001 where id = 123"
+---------------+
| column001     |
+---------------+
| foo           |
+---------------+

Let's update column001 on only the master.

[root@master ~] mysql -e "update db1.table001 set column001 = 'bar' where id = 123"

Reissuing the select command should show that the change was made on the master and then immediately replicated to the slave.

[root@master ~] mysql -e "select column001 from db1.table001 where id = 123"
+---------------+
| column001     |
+---------------+
| bar           |
+---------------+

[root@slave ~] mysql -e "select column001 from db1.table001 where id = 123"
+---------------+
| column001     |
+---------------+
| bar           |
+---------------+