MySQL/MariaDB Database 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.



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 Jelastic PaaS.

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

One-click Installation

You can get a MySQL cluster with two databases up and running within minutes using Jelastic one-click install option:



As well, as MariaDB's one:



The process is simple.

Just click Get it hosted now and type your email. You’ll get an environment with replicated master and slave databases just in a minute, skipping the steps of manual installation.

Note that current widget is provided for beta testing of automated Master-Slave DB replication adjustment. Therefore you should take into consideration a few peculiarities it has:

  • after the environment creation you’ll receive just one email with admin credentials to your master database
  • slave DB can be accessed only via SSH protocol using master database credentials


The complete and full-featured one-click solution will be provided in the nearest future.

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.

  1. Create environments

  2. *The instruction below is fully suitable for MySQL database servers.


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

    1. Log in to
      Jelastic Manager
    2. Ask Jelastic to create a new 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.


    4. Wait just a minute for your environment to be created.



    5. 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.




  3. Configure master database

  4. Let's configure master base now.

    1. Click Config button for your master database.



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

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



      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!)

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



    5. Click the Open in browser button for MariaDB. Jelastic sent you an email with credentials to the database. Log in using these credentials.

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



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

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

      Click Go at the bottom of the page.

  5. Configure slave database
  6. Let's go back to the Jelastic dashboard and configure our slave base.

    1. Click Config button for your slave database.



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

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



      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.

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



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

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



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


    8. Now you master server is configured.



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



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




  7. Check the results
  8. We have to ensure now that master-slave replication works for our databases

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



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




  9. Connection to master-slave
  10. 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.

    2. 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;
          }
      }
    3. Connection to master and slave databases for your PHP application:
    4. <?php
      /* Master settings */
      $master_server = "xx.xxx.x.xx";
      $master_username = "root";
      $master_password = "abcABC123";
      
      /* Slave settings */
      $slave_server = "xx.xxx.x.xx";
      $slave_username = "root";
      $slave_password = "abcABC123";
      
      $link_to_master = mysqli_connect(
      $master_server,
      $master_username,
      $master_password,
      'mysql');
      
      if (!$link_to_master) {
      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!