MySQL Replication Setup

Mysql uses a Master-slave/Publisher-Subscriber model for Replication. MySQL replication is an asynchronous replication. In MySQL replication master keeps a log of all of the updates performed on the database. Then, one or more slaves connect to the Master(Publisher Server), read each log entry, and perform the indicated update on the slave (Subscriber) server databases. The master server is responsible for the track of log rotation and access control.

Each slave server has to keep the track of current position within the server's transaction log. As new transactions occur on the server, they get logged on the master server and downloaded by each slave. Once the transaction has been committed by each slave, the slaves update their position in the server's transaction log and wait for the next transaction.

In this article, I will show you the steps to configure the Master/Slave replication between two servers.

Step 1: Create a user on Master server which Slave server can use to connect. I have created the user named "repl_user".
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot
--Execute the below code
GRANT REPLICATION SLAVE ON *.* TO 'repl_user'@'%' IDENTIFIED BY 'password';
FLUSH PRIVILEGES;
[/sourcecode]

Step 2: We have to change the MySQL configuration file usually in the /etc/mysql.cnf location. Here we will add the replication configuration parameters.

log-bin – will be used to write a log on the desired location
binlog-do-db – will be used to enabled the database for writing log. I have used Publisher_Database, you have to specify your database name.
server-id – Specify the ID of the Master server

[sourcecode language="sql"]
log-bin = /home/mysql/logs/mysql-bin.log
binlog-do-db=publisher_database
server-id=1
[/sourcecode]

Step 3: Once you have added the above configuration parameters into the My.cnf, next step is restart the MySQL Master Instance.
You can use below command to restart the MySQl service.
[sourcecode language="sql"]
/etc/init.d/mysqld restart
service mysqld restart
[/sourcecode]

Step 4: We have to configure the /etc/my.cnf file on the slave server. Here we will add the below parameters in the configuration file.

server-id - gives the Slave its unique ID
master-host - tells the Slave the I.P address of the Master server for connection. You can get the IP address using IPConfig command.
master-connect-retry - Here we will specify the connection retry interval.
master-user - Specify the user which has permission access the Master server
master-password - Specify the password of the replication user mentioned above
replicate-do-db - Specify the subscriber database name
relay-log - direct slave to use relay log

[sourcecode language="sql"]
server-id=2
master-host=128.20.30.1
master-connect-retry=60
master-user=repl_user
master-password=password
replicate-do-db=subscriber_slave
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index
[/sourcecode]

Step 5: Restart the slave MySQl instance
[sourcecode language="sql"]
/etc/init.d/mysqld restart
service mysqld restart
[/sourcecode]

Step 6: If your Master MySQL instance is live instance, you have to do the backup/restore using MySQLDump utility.
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot

--Stop the write operation
FLUSH TABLES WITH READ LOCK;

--Generate the dump of the database (backup)
--gzip command will compress the file and create the zip file name backup.sql.gz
mysqldump publisher_master -u root -p > /home/my_home_dir/backup.sql;
gzip /home/my_home_dir/backup.sql;

--execute below copy command on slave to copy the backup file
scp root@128.20.30.1:/home/my_home_dir/database.sql.gz /home/my_home_dir/

--Once copied, extract the file using gunzip
gunzip /home/my_home_dir/backup.sql.gz

--restore the databsae
mysql -u root -p subscriber_slave </home/my_home_dir/backup.sql

[/sourcecode]

Step 7: Execute the SHOW MASTER STATUS command on Master server. It will give you the bin log file name and position which we will use specify the slave.
[sourcecode language="sql"]
SHOW MASTER STATUS;
[/sourcecode]

+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 | 707 | exampledb | |
+------------------+----------+--------------+------------------+


Step 8: Execute the below commands on slave.
[sourcecode language="sql"]
--Connect to MySQL Slave server
mysql -u root -proot
--stop the slave
slave stop;
-- Execute the below command
CHANGE MASTER TO MASTER_HOST='128.20.30.1', MASTER_USER='repl_user', MASTER_PASSWORD='password', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=707;
--Start the Slave
slave start;
[/sourcecode]

Step 9: Login to Master MySQL instance and unlock the tables.
[sourcecode language="sql"]
--Connect to MySQL Master server
mysql -u root -proot
-- unlock the tables if you have executed lock tables command
unlock tables;
[/sourcecode]

You are all set. Master to Slave replication has been started. Make sure while configuring the my.cnf file.
1. Take the copy of my.cnf file before starting the replication configuration.
2. Make sure skip-networking parameter is not enabled in the my.cnf file.