How to setup a slave for replication in 6 simple steps with Percona XtraBackup

Data is, by far, the most valuable part of a system. Having a backup done systematically and available for a rapid recovery in case of failure is admittedly essential to a system. However, it is not common practice because of its costs, infrastructure needed or even the boredom associated to the task. Percona XtraBackup is designed to solve this problem.

You can have almost real-time backups in 6 simple steps by setting up a replication environment with Percona XtraBackup.

Percona XtraBackup is a tool for backing up your data extremely easy and without interruption. It performs “hot backups” on unmodified versions of MySQL servers (5.1, 5.5 and 5.6), as well as MariaDB and Percona Servers. It is a totally free and open source software distributed only under the GPLv2 license.

All the things you will need

Setting up a slave for replication with Percona XtraBackup is really a very straightforward procedure. In order to keep it simple, here is a list of the things you need to follow the steps without hassles:

  • TheMaster A system with a MySQL-based server installed, configured and running. This system will be called TheMaster, as it is where your data is stored and the one to be replicated. We will assume the following about this system:
    • the MySQL server is able to communicate with others by the standard TCP/IP port;
    • the SSH server is installed and configured;
    • you have a user account in the system with the appropriate permissions;
    • you have a MySQL’s user account with appropriate privileges.
    • server has binlogs enabled and server-id set up to 1.
  • TheSlave Another system, with a MySQL-based server installed on it. We will refer to this machine as TheSlave and we will assume the same things we did about TheMaster, except that the server-id on TheSlave is 2.
  • Percona XtraBackup The backup tool we will use. It should be installed in both computers for convenience.

STEP 1: Make a backup on TheMaster and prepare it

At TheMaster, issue the following to a shell:

TheMaster$ innobackupex --user=yourDBuser --password=MaGiCdB1 /path/to/backupdir

After this is finished you should get:

innobackupex: completed OK!

This will make a copy of your MySQL data dir to the /path/to/backupdir/$TIMESTAMP. You have told Percona XtraBackup (through the innobackupex script) to connect to the database server using your database user and password, and do a hot backup of all your data in it (all MyISAM, InnoDB tables and indexes in them).

In order for snapshot to be consistent you need to prepare the data:

TheMaster$ innobackupex --user=yourDBuser --password=MaGiCdB1 \
           --apply-log /path/to/backupdir/$TIMESTAMP/

You need to select path where your snapshot has been taken, for example /home/backups/2012-01-16_11-14-43. If everything is ok you should get the same OK message. Now the transaction logs are applied to the data files, and new ones are created: your data files are ready to be used by the MySQL server.

Percona XtraBackup knows where your data is by reading your my.cnf. If you have your configuration file in a non-standard place, you should use the flag --defaults-file =/location/of/my.cnf.

If you want to skip writing the username/password every time you want to access MySQL, you can set it up in your $HOME folder. Just edit .my.cnf and add:

[client]
user=root
pass=MaGiCdB1

This is will give you root access to MySQL.

STEP 2: Copy backed up data to TheSlave

Use rsync or scp to copy the data from Master to Slave. If you’re syncing the data directly to slave’s data directory it’s advised to stop the mysqld there.

TheMaster$ rsync -avprP -e ssh /path/to/backupdir/$TIMESTAMP TheSlave:/path/to/mysql/

After data has been copied you can back up the original or previously installed MySQL datadir (NOTE: Make sure mysqld is shut down before you move the contents of its datadir, or move the snapshot into its datadir.):

TheSlave$ mv /path/to/mysql/datadir /path/to/mysql/datadir_bak

and move the snapshot from TheMaster in its place:

TheSlave$ mv /path/to/mysql/$TIMESTAMP /path/to/mysql/datadir

After you copy data over, make sure MySQL has proper permissions to access them.

TheSlave$ chown mysql:mysql /path/to/mysql/datadir

In case the ibdata and iblog files are located in different directories outside of the datadir, you will have to put them in their proper place after the logs have been applied.

STEP 3: Configure The Master’s MySQL server

Add the appropriate grant in order for slave to be able to connect to master:

TheMaster|mysql> GRANT REPLICATION SLAVE ON *.*  TO 'repl'@'$slaveip'
 IDENTIFIED BY '$slavepass';

Also make sure that firewall rules are correct and that TheSlave can connect to TheMaster. Test that you can run the mysql client on TheSlave, connect to TheMaster, and authenticate.

TheSlave$ mysql --host=TheMaster --user=repl --password=$slavepass

Verify the privileges.

mysql> SHOW GRANTS;

STEP 4: Configure The Slave’s MySQL server

First copy the my.cnf file from TheMaster to TheSlave:

TheSlave$ scp user@TheMaster:/etc/mysql/my.cnf /etc/mysql/my.cnf

then change the following options in /etc/mysql/my.cnf:

server-id=2

and start/restart mysqld on TheSlave.

In case you’re using init script on Debian based system to start mysqld, be sure that the password for debian-sys-maint user has been updated and it’s the same as that user’s password on the TheMaster. Password can be seen and updated in /etc/mysql/debian.cnf.

STEP 5: Start the replication

Look at the content of the file xtrabackup_binlog_info, it will be something like:

TheSlave$ cat /var/lib/mysql/xtrabackup_binlog_info
TheMaster-bin.000001     481

Execute the CHANGE MASTER statement on a MySQL console and use the username and password you’ve set up in STEP 3:

TheSlave|mysql> CHANGE MASTER TO
                MASTER_HOST='$masterip',
                MASTER_USER='repl',
                MASTER_PASSWORD='$slavepass',
                MASTER_LOG_FILE='TheMaster-bin.000001',
                MASTER_LOG_POS=481;

and start the slave:

TheSlave|mysql> START SLAVE;

STEP 6: Check

You should check that everything went OK with:

TheSlave|mysql> SHOW SLAVE STATUS \G
         ...
         Slave_IO_Running: Yes
         Slave_SQL_Running: Yes
         ...
         Seconds_Behind_Master: 13
         ...

Both IO and SQL threads need to be running. The Seconds_Behind_Master means the SQL currently being executed has a current_timestamp of 13 seconds ago. It is an estimation of the lag between TheMaster and TheSlave. Note that at the beginning, a high value could be shown because TheSlave has to “catch up” with TheMaster.

Adding more slaves to The Master

You can use this procedure with slight variation to add new slaves to a master. We will use Percona XtraBackup to clone an already configured slave. We will continue using the previous scenario for convenience but we will add TheNewSlave to the plot.

At TheSlave, do a full backup:

TheSlave$ innobackupex --user=yourDBuser --password=MaGiCiGaM /
          --slave-info /path/to/backupdir

By using the --slave-info Percona XtraBackup creates additional file called xtrabackup_slave_info.

Apply the logs:

TheSlave$ innobackupex --apply-log --use-memory=2G /path/to/backupdir/$TIMESTAMP/

Copy the directory from the TheSlave to TheNewSlave (NOTE: Make sure mysqld is shut down on TheNewSlave before you copy the contents the snapshot into its datadir.):

rsync -avprP -e ssh /path/to/backupdir/$TIMESTAMP TheNewSlave:/path/to/mysql/datadir

Add additional grant on the master:

TheMaster|mysql> GRANT REPLICATION SLAVE ON *.*  TO 'repl'@'$newslaveip'
             IDENTIFIED BY '$slavepass';

Copy the configuration file from TheSlave:

TheNEWSlave$ scp user@TheSlave:/etc/mysql/my.cnf /etc/mysql/my.cnf

Make sure you change the server-id variable in /etc/mysql/my.cnf to 3 and disable the replication on start:

skip-slave-start
server-id=3

After setting server_id, start mysqld.

Fetch the master_log_file and master_log_pos from the file xtrabackup_slave_info, execute the statement for setting up the master and the log file for The NEW Slave:

TheNEWSlave|mysql> CHANGE MASTER TO
                   MASTER_HOST='$masterip',
                   MASTER_USER='repl',
                   MASTER_PASSWORD='$slavepass',
                   MASTER_LOG_FILE='TheMaster-bin.000001',
                   MASTER_LOG_POS=481;

and start the slave:

TheSlave|mysql> START SLAVE;

If both IO and SQL threads are running when you check the TheNewSlave, server is replicating TheMaster.

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