How To Set Up MySQL Database Replication

***Configuring The Master (server1)***

On the MySQL shell, run the following commands:

GRANT REPLICATION SLAVE ON *.* TO 'slavedb'@'%' IDENTIFIED BY 'slavepasswd';
FLUSH PRIVILEGES;
quit;


Furthermore we have to tell MySQL for which database it should write logs (these logs are used by the slave to see what has changed on the master),

which log file it should use, and we have to specify that this MySQL server is the master. We want to replicate the database exampledb, so we

add/enable the following lines in /etc/mysql/my.cnf (in the [mysqld]section):

vi /etc/mysql/my.cnf

[...]
# The following can be used as easy to replay backup logs or for replication.
# note: if you are setting up a replication slave, see README.Debian about
# other settings you may need to change.
server-id = 1
log_bin = /var/log/mysql/mysql-bin.log
expire_logs_days = 10
max_binlog_size = 100M
binlog_do_db = exampledb
[...]


Then restart MySQL:

/etc/init.d/mysqld restart


Next we lock the exampledb database on server1, find out about the master status of server1, create an SQL dump of exampledb (that we will import

into exampledb on server2 so that both databases contain the same data), and unlock the database so that it can be used again:

mysql -u root -p


On the MySQL shell, run the following commands:

USE exampledb;
FLUSH TABLES WITH READ LOCK;
SHOW MASTER STATUS;

The last command should show something like this (please write it down, we'll need it later on):

mysql> SHOW MASTER STATUS;
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 | 98 | exampledb | |
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec)


Now don't leave the MySQL shell, because if you leave it, the database lock will be removed, and this is not what we want right now because we must

create a database dump now. While the MySQL shell is still open, we open a second command line window where we create the SQL dump

snapshot.sql and transfer it to server2 (using scp; again, make sure that the root account is enabled on server2):

server1:

cd /tmp
mysqldump -u root -pyourrootsqlpassword --opt exampledb > snapshot.sql
scp snapshot.sql root@192.168.0.101:/tmp


Afterwards, you can close the second command line window. On the first command line window, we can now unlock the database and leave the MySQL shell:

server1:

UNLOCK TABLES;
quit;


***Configuring The Slave (server2)***

Now we must configure the slave. Open /etc/mysql/my.cnf and make sure you have the following settings in the [mysqld] section:

server2:

vi /etc/mysql/my.cnf

[...]
server-id=2
master-connect-retry=60
replicate-do-db=exampledb
[...]


The value of server-id must be unique and thus different from the one on the master!

Restart MySQL afterwards:

/etc/init.d/mysqld restart


Before we start setting up the replication, we create an empty database exampledb on server2:

mysql -u root -p

CREATE DATABASE exampledb;
quit;


On server2, we can now import the SQL dump snapshot.sql like this:

/usr/bin/mysqladmin --user=root --password=yourrootsqlpassword stop-slave
cd /tmp
mysql -u root -pyourrootsqlpassword exampledb < snapshot.sql


Now connect to MySQL again...

mysql -u root -p


... and run the following command to make server2 a slave of server1 (it is important that you replace the values in the following command with the values you got from the SHOW MASTER STATUS; command that we ran on server1!):

CHANGE MASTER TO MASTER_HOST='192.168.0.100', MASTER_USER='slave_user', MASTER_PASSWORD='slave_password', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

MASTER_HOST is the IP address or hostname of the master (in this example it is 192.168.0.100).
MASTER_USER is the user we granted replication privileges on the master.
MASTER_PASSWORD is the password of MASTER_USER on the master.
MASTER_LOG_FILE is the file MySQL gave back when you ran SHOW MASTER STATUS; on the master.
MASTER_LOG_POS is the position MySQL gave back when you ran SHOW MASTER STATUS; on the master.


Finally start the slave:

START SLAVE;

Then check the slave status:

SHOW SLAVE STATUS \G

It is important that both Slave_IO_Running and Slave_SQL_Running have the value Yes in the output (otherwise something went wrong, and you should

check your setup again and take a look at /var/log/syslog to find out about any errors);

mysql> SHOW SLAVE STATUS \G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.0.100
Master_User: slave_user
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000001
Read_Master_Log_Pos: 98
Relay_Log_File: mysqld-relay-bin.000002
Relay_Log_Pos: 235
Relay_Master_Log_File: mysql-bin.000001
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB: exampledb
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: 98
Relay_Log_Space: 235
Until_Condition: None
Until_Log_File:
Until_Log_Pos: 0
Master_SSL_Allowed:
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master: 0
1 row in set (0.00 sec)


Afterwards, you can leave the MySQL shell on server2:

quit;

That's it! Now whenever exampledb is updated on the master, all changes will be replicated to exampledb on the slave. Test it!