The Perfect Load-Balanced & High-Availability Web Cluster With 2 Servers Running Xen On Ubuntu 8.04 Hardy Heron - Page 4

10. MySQL replication (web1, web2)

10.1 Mysql Installing MySQL 5.0

apt-get install mysql-server-5.0 mysql-client-5.0

To make sure that the replication can work, we must make MySQL listen on all interfaces, therefore we comment out the line bind-address = 127.0.0.1 in /etc/mysql/my.cnf :

vi /etc/mysql/my.cnf

[...]
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
#bind-address           = 127.0.0.1
[...]

Restart MySQL afterwards :

/etc/init.d/mysql restart

On web1

Now we set up a replication user slave2_user that can be used by web2.example.com to access the MySQL database :

mysql -u root -p

On the MySQL shell, run the following commands :

GRANT REPLICATION SLAVE ON *.* TO 'slave2_user'@'%' IDENTIFIED BY 'slave2_password';
FLUSH PRIVILEGES;
quit;

On web2

Now we do the last two steps again on web2.example.com :

mysql -u root -p

GRANT REPLICATION SLAVE ON *.* TO 'slave1_user'@'%' IDENTIFIED BY 'slave1_password';
FLUSH PRIVILEGES;
quit;

On web1 AND web2

We will now create a database that will be used later for the mail server :

mysqladmin -u root -p create mail

Next, we go to the MySQL shell:

mysql -u root -p

On the MySQL shell, we create the user mail_admin with the passwort mail_admin_password (replace it with your own password) who has SELECT,INSERT,UPDATE,DELETE privileges on the mail database. This user will be used by Postfix and Courier to connect to the mail database:

GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost' IDENTIFIED BY 'mail_admin_password';
GRANT SELECT, INSERT, UPDATE, DELETE ON mail.* TO 'mail_admin'@'localhost.localdomain' IDENTIFIED BY 'mail_admin_password';
FLUSH PRIVILEGES;
quit;

10.2 Setting Up Replication

Now we set up master-master replication in /etc/mysql/my.cnf. The crucial configuration options for master-master replication are auto_increment_increment and auto_increment_offset:

auto_increment_increment controls the increment between successive AUTO_INCREMENT values.
auto_increment_offset determines the starting point for AUTO_INCREMENT column values.

Let's assume we have N MySQL nodes (N=2 in this example), then auto_increment_increment has the value N on all nodes, and each node must have a different value for auto_increment_offset (1, 2, ..., N).

Now let's configure our two MySQL nodes:

On web1

vi /etc/mysql/my.cnf

add the following lines right below "[mysqld]":

server-id = 1
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 1
#use 192.168.1.105 if you didnt install a crossover cable on eth1
master-host = 192.168.0.105
master-user = slave1_user
master-password = slave1_password
master-connect-retry = 60
replicate-do-db = mail
log-bin = /var/log/mysql/mysql-bin.log
binlog-do-db = mail
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

and modify the line "max_binlog_size" :

[...]
max_binlog_size         = 500M
[...]

/etc/init.d/mysql restart

On web2

vi /etc/mysql/my.cnf

server-id = 2
replicate-same-server-id = 0
auto-increment-increment = 2
auto-increment-offset = 2
#use 192.168.1.104 if you didnt install a crossover cable on eth1
master-host = 192.168.0.104
master-user = slave2_user
master-password = slave2_password
master-connect-retry = 60
replicate-do-db = mail
log-bin = /var/log/mysql/mysql-bin.log
binlog-do-db = mail
relay-log = /var/lib/mysql/slave-relay.log
relay-log-index = /var/lib/mysql/slave-relay-log.index

and modify the line "max_binlog_size" :

[...]
max_binlog_size         = 500M
[...]

/etc/init.d/mysql restart

On web1 AND web2

Now we will start replication :

mysql -u root -p

On the MySQL shell, run the following commands:

reset master;
stop slave;
reset slave;

Now run the following :

On web1

CHANGE MASTER TO MASTER_HOST='192.168.0.105', MASTER_USER='slave1_user', MASTER_PASSWORD='slave1_password', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

start slave;
quit;

On web2

CHANGE MASTER TO MASTER_HOST='192.168.0.104', MASTER_USER='slave2_user', MASTER_PASSWORD='slave2_password', MASTER_LOG_FILE='mysql-bin.000001', MASTER_LOG_POS=98;

start slave;
quit;

Now replication should work.

10.3 Testing replication

On web1 AND web2

mysql -u root -p

On the MySQL shell, run the following commands:

show slave status \G;

There are 3 important lines in the output that should look like this :

[...]
Slave_IO_State: Waiting for master to send event
[...]
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB: mail
[...]

Now you can quit mysql :

quit;

On web1

We will insert some data on web1.example.com for testing and that will serve in the next chapter for mail :

mysql -u root -p

On the MySQL shell, run the following commands:

use mail;

We will create the following tables :

CREATE TABLE domains (
domain varchar(50) NOT NULL,
transport varchar(128) NOT NULL default 'smtp:[192.168.1.104]',
PRIMARY KEY (domain) )
TYPE=MyISAM;

CREATE TABLE forwardings (
source varchar(80) NOT NULL,
destination TEXT NOT NULL,
PRIMARY KEY (source) )
TYPE=MyISAM;

CREATE TABLE users (
email varchar(80) NOT NULL,
password varchar(20) NOT NULL,
quota INT(10) DEFAULT '10485760',
PRIMARY KEY (email)
) TYPE=MyISAM;

CREATE TABLE transport (
domain varchar(128) NOT NULL default '',
transport varchar(128) NOT NULL default '',
UNIQUE KEY domain (domain)
) TYPE=MyISAM;

quit;

These freshly create tables should appear on web2 mail database as well, thanks to replication.

On web2

Now we will verify that :

mysql -u root -p

On the MySQL shell, run the following commands:

use mail;
show tables;

The output should be :

+----------------+
| Tables_in_mail |
+----------------+
| domains         |
| forwardings    |
| transport        |
| users              |
+----------------+
4 rows in set (0.00 sec)

quit;

If you see that replication is working.