Master Slave Replication

Master-slave replication is used to solve a number of different problems with performance, supporting the backup of different databases, and as a part of a larger solution to alleviate system failures. It enables data from one database server (the master) to be replicated to one or more database servers (the slaves). The master logs the updates, which then ripple through to the slaves. The slave outputs a message stating that it has received the update successfully, thus allowing to send the subsequent updates. Master-slave replication can be either synchronous or asynchronous. The difference is simply the timing of propagation of changes. If the changes are made to the master and slave at the same time, it is synchronous. If changes are queued up and written later, it is asynchronous.

database master-slave replication

The target usage for replication in MariaDB and MySQL databases includes:

  • Scale-out solutions
  • Data security
  • Analytics
  • Long-distance data distribution

How you can use such replication and take advantage of it:

  • Backups: to use replication as a backup solution, replicate data from the master to a slave, and then back up the data slave. The slave can be paused and shut down without affecting the running operation of the master, so you can produce an effective snapshot of “live” data that would otherwise require the master to be shut down.
  • Scale-out: you can use replication as a scale-out solution; that is, where you want to split up the load of database queries across multiple database servers, within some reasonable limitations. Because replication works from the distribution of one master to one or more slaves, using replication for scale-out works best in an environment where you have a high number of reads and low number of writes/updates.
  • Spreading the load: there may be situations when you have a single master and want to replicate different databases to different slaves. For example, you may want to distribute different sales data to different departments to help spread the load during data analysis.
  • Increasing the performance: as the number of slaves connecting to a master increases, the load, although minimal, also increases, as each slave uses a client connection to the master. Also, as each slave must receive a full copy of the master binary log, the network load on the master may also increase and create a bottleneck. If you are using a large number of slaves connected to one master, and that master is also busy processing requests (for example, as a part of a scale-out solution), then you may want to improve the performance of the replication process. One way to improve the performance of the replication process is to create a deeper replication structure that enables the master to replicate to only one slave, and for the remaining slaves to connect to this primary slave for their individual replication requirements.
  • Failover alleviating: You can set up a master and a slave (or several slaves), and to write a script that monitors the master to check whether it is up. Then instruct your applications and the slaves to change master in case of failure.
  • Security: you can use SSL for encrypting the transfer of the binary log required during replication, but both the master and the slave must support SSL network connections. If either host does not support SSL connections, replication through an SSL connection is not possible. Setting up replication using an SSL connection is similar to setting up a server and client using SSL. You must obtain (or create) a suitable security certificate that you can use on the master, and a similar certificate (from the same certificate authority) on each slave.

Now let’s examine a simple example on how to configure master-slave replication on CirrusGrid PaaS.

You are able to set a DB cluster in a two ways:

One-Click Installation #

You can get a MySQL or MariaDB database cluster with required replication type (including the master-slave one) up and running within minutes via CirrusGrid marketplace.

The process is simple – just provide your email and confirm via the appropriate notification. Read the MariaDB/MySQL Auto-Clustering article for more information on the installed package and available customization options.

Manual Installation #

If you prefer to configure the Master-Slave replication manually in order to get more slave replicators or specify some custom configurations, please, follow the instruction below.

Create Environments #

Tip: The instruction below is fully suitable for MySQL database servers.

First of all we create two environments in CirrusGrid for our master and slave databases.

1. Log in to CirrusGrid dashboard.

2. Ask CirrusGrid to create a new environment.

create environment

3. In the Environment topology dialog pick MariaDB (or MySQL) as a database you want to use. Set the cloudlet limit and type the name of your first environment, for example, masterbase.

environment wizard

Wait just a minute for your environment to be created.

replica master environment

4. In the same way create one more environment with MariaDB or just clone it. Let’s name it slavebase. It will be located on the other hardnode, what is even more secure and reliable for storing your data.

Now you have two identical environments with two databases.

replica slave environment

Configure Master Database #

Let’s configure master base now.

1. Click Config button for your master database.

MariaDB config

2. Navigate to my.cnf file and add the following properties as it is shown below:

server-id = 1  
log-bin = mysql-bin  
binlog-format=mixed

my.cnf configs

We use binlog format “mixed” (binlog-format=mixed) to allow a replication of operations with foreign keys.

Note: Do not use binlog format “statement”. Otherwise you will get errors later on!

3. Save the changes and restart MariaDB in order to apply the new configuration parameters.

MariaDB restart

4. Click the Open in Browser button for MariaDB. CirrusGrid sent you an email with credentials to the database. Log in using these credentials.

5. Navigate to the User accounts tab and click on Add user account.

database add user

6. Specify the name and password for your slave replication user.

database user credentials

Now, scroll down and tick the replication client and replication slave administration privileges.

database replication privileges

Click Go at the bottom of the page.

Configure Slave Database #

Let’s go back to the CirrusGrid dashboard and configure our slave base.

1. Click Config button for your slave database.

slave database config

2. Navigate to my.cnf file and add the following strings:

server-id = 2  
slave-skip-errors = all

slave mycnf configs

We allow our slave base to skip all errors from master (slave-skip-errors = all) in order not to stop normal slave operation in case of errors on master base.

This skipping is not recommended for using at the development stage in order to find out bugs etc. But here we talk about production, when your code has been already tested. Any error on the master’s side can stop slave or lead to its unsynchronization. In this case the error may be even innocuous. Some minor errors will probably occur on production. So the replication can be stopped because of small errors.

3. Next, open the /etc/phpMyAdmin/config.inc.php file and append it with the next option:

$cfg['AllowArbitraryServer'] = true;

slave allow arbitrary server

4. Save the changes and restart your slave database server in order to apply the new configuration parameters.

MariaDB restart

5. Navigate to phpMyAdmin using the credentials which CirrusGrid sent you when you created the environment for your slave database.

6. Go to the Replication tab click Configure for Slave replication.

configure slave replication

7. Configure your master server (enter the name, the password and the host of your slave replication user).

slave replication user

Now you master server is configured.

master server configured

8. Click on Control slave > Full start for the slave server in order to run Slave SQL and Slave IO threads.

slave full start

9. Check the slave status table to ensure that everything is ok.

slave status

Check the Results #

We have to ensure now that master-slave replication works for our databases.

1. Let’s create the new database (e.g. CirrusGrid) in our master base.

create new database

2. Navigate to slave base and you’ll see that the new database was successfully replicated.

new database replicated

Connection to Master-Slave #

Here are two examples on how to connect to your master and slave databases from Java and PHP application.

1. As an example here you can see the code of our Java application which connects to master and slave databases.

Database_config.cfg:

master_host=jdbc:mysql://mariadb-master-host/mysql
master_username=root
master_password=abcABC123

slave_host=jdbc:mysql://mariadb-slave-host/mysql
slave_username=root
slave_password=abcABC123

driver=com.mysql.jdbc.Driver

Dbmanager.java:

package com.jelastic.test;
import java.io.FileInputStream;
import java.io.IOException;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
import java.util.Properties;
import java.util.logging.Level;
import java.util.logging.Logger;

public class DbManager {

    private final static String createDatabase = "CREATE SCHEMA IF NOT EXISTS jelastic";
    private final static String showDatabases = "SHOW DATABASES";

    public Connection createMasterConnection() throws IOException, ClassNotFoundException, SQLException {
       Connection masterConnection;
       Properties prop = new Properties();
       prop.load(new FileInputStream(System.getProperty("user.home") + "/database_config.cfg"));
       String master_host = prop.getProperty("master_host").toString();
       String master_username = prop.getProperty("master_username").toString();
       String master_password = prop.getProperty("master_password").toString();
       String driver = prop.getProperty("driver").toString();

       Class.forName(driver);
       masterConnection = DriverManager.getConnection(master_host, master_username, master_password);
       return masterConnection;
    }

    public Connection createSlaveConnection() throws IOException, ClassNotFoundException, SQLException {
       Connection slaveConnection;
       Properties prop = new Properties();
       prop.load(new FileInputStream(System.getProperty("user.home") + "/database_config.cfg"));
       String slave_host = prop.getProperty("slave_host").toString();
       String slave_username = prop.getProperty("slave_username").toString();
       String slave_password = prop.getProperty("slave_password").toString();
       String driver = prop.getProperty("driver").toString();

       Class.forName(driver);
       slaveConnection = DriverManager.getConnection(slave_host, slave_username, slave_password);
       return slaveConnection;
    }

    public boolean runSqlStatementOnMaster() {
       boolean execute = false;
       Statement statement = null;
       try {
           statement = createMasterConnection().createStatement();
           execute = statement.execute(createDatabase);
       } catch (IOException ex) {
         Logger.getLogger(DbManager.class.getName()).log(Level.SEVERE, null, ex);
       } catch (ClassNotFoundException ex) {
         Logger.getLogger(DbManager.class.getName()).log(Level.SEVERE, null, ex);
       } catch (SQLException ex) {
           ex.printStackTrace();
       } finally {
           if (statement != null) {
               try {
                   statement.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
       }
       return execute;
    }
    
    public List<String> runSqlStatementOnSlave() {
       List<String> stringList = new ArrayList<String>();
       Statement statement = null;
       ResultSet resultSet = null;
       try {
           statement = createSlaveConnection().createStatement();
           resultSet = statement.executeQuery(showDatabases);
           while (resultSet.next()) {
               stringList.add(resultSet.getString(1));
           }
       } catch (IOException ex) {
         Logger.getLogger(DbManager.class.getName()).log(Level.SEVERE, null, ex);
       } catch (ClassNotFoundException ex) {
         Logger.getLogger(DbManager.class.getName()).log(Level.SEVERE, null, ex);
       } catch (SQLException ex) {
           ex.printStackTrace();
       } finally {
           if (resultSet != null) {
               try {
                   resultSet.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
           if (statement != null) {
               try {
                   statement.close();
               } catch (SQLException e) {
                   e.printStackTrace();
               }
           }
       }
       return stringList;
    }
}

2. Connection to master and slave databases for your PHP application:

er) {
printf("Unable to connect master database server. Error: %s\n", mysqli_connect_error());
exit;
}

$link_to_slave = mysqli_connect(
$slave_server,
$slave_username,
$slave_password,
'mysql');

if (!$link_to_slave) {
printf("Unable to connect slave database server. Error: %s\n", mysqli_connect_error());
exit;
}

print("
Creating database with name Jelastic on Master node ");

$result = mysqli_query($link_to_master, 'CREATE DATABASE JelasticX');

sleep (3);

print("
Checking if created database was replciated to slave ");

if ($result = mysqli_query($link_to_slave, 'SHOW DATABASES LIKE "JelasticX"')) {
$result_text = mysqli_fetch_array($result);
print ("
Replicated database is ".$result_text[0]);
}

mysqli_close($link_to_master);
mysqli_close($link_to_slave);
?>

Now you have your own database replication in the cloud. Enjoy!

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