Failover is a procedure by which a system automatically transfers control to a duplicate system when it detects a fault or failure. A failover can be Automatic or Manual

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2. Index
• What is Failover / DR / Redundant Site
• What is Replication
• How database replication works
• Advantages of Replication
• Types of Database Replications
• How to setup replication
• How to Monitor Replication
• Failover Steps
• Reverse Failover Steps

3. What is Failover?
Failover is a procedure by which a system automatically transfers control to
a duplicate system when it detects a fault or failure. A failover can be
Automatic or Manual

4. What is Replication?
Replication enables data from one server (the master) to be replicated to
one or more servers (the slaves).

5. How MySQL Database
Replication works?
MySQL Replication is asynchronous. slaves need not be connected
permanently to receive updates from the master. This means that updates
can occur over long-distance connections. Depending on the configuration,
you can replicate all databases, selected databases, or even selected tables
within a database

6. Advantages of MySQL
Database Replication
• Scale-out solutions
spreading the load among multiple slaves to improve performance. In this
environment, all writes and updates must take place on the master server.
Reads, however, may take place on one or more slaves. This model can improve
the performance of writes (since the master is dedicated to updates), while
dramatically increasing read speed across an increasing number of slaves.
• Data security
because data is replicated to the slave, and the slave can pause the replication
process, it is possible to run backup services on the slave without corrupting the
corresponding master data.
• Analytics
live data can be created on the master, while the analysis of the information
can take place on the slave without affecting the performance of the master.
• Long-distance data distribution
if a branch office would like to work with a copy of your main data, you can use
replication to create a local copy of the data for their use without requiring
permanent access to the master.

7. Types of MySQL Database
Replication
• Unidirectional Replication
• Bi-Directional Replication
• Directed Replication
• Multi Slave Replication
• Circular Replication

8. Unidirectional Replication
Data is replicated from single master to single slave server, it involves 2
servers. This setup is usually used for backups.

9. Bi-Directional Replication
This setup involves 2 servers, both being masters to the other as well as
both being slaves to the other. This setup can be used as failover.

10. Multi Slave Replication
This setup involves minimum 3 servers, “Server A” being master, “Server B”
and “Server C” being slave to “Server A”.

11. Directed Replication
This setup involves minimum 3 servers, “Server A” being master, “Server B”
being slave to “Server A” as well as master to all other Slaves. This setup
increases performance of “Server A”, because All slaves are directly
connected to “Server B” and “Server A” only serves “Server B” for
replication

12. Circular Replication
This setup involves minimum 3 servers, “Server A” being master, “Server B”
being slave to “Server A” as well as master to “Server C”, and “Server C”
being slave to “Server B” as well as master to “Server A”

13. How to Setup Replication
1. Add below directives in MySQL configuration file (my.cnf) and restart
MySQL services
server-id=1
log-bin=mysql-bin
log-error=mysql-bin.err
2. Connect Master Server and Add Replication User (Recommended)
3. Connect each Slave Server and execute below command
mysql> CHANGE MASTER TO MASTER_HOST=‘master_ip',
MASTER_USER='replication_username', MASTER_PASSWORD='replication_password‘;
mysql> Start Slave;

14. How to Monitor Replication
1. Connect to Slave Server and execute below statement to monitor status.
mysql> Show Slave Status;
2. Value of ‘Slave_IO_Running’ and ‘Slave_SQL_Running’ should be “YES”.
3. If either is “No”, There are possibilities that MySQL Replication is
broken.

15. Failover Steps
If multiple slaves exists and all were configured to get updates from the “Slave A”.
(“Slave A” is down and we are switching our updates to “Slave B”) and we have to
configure “Slave C” to get updates from “Slave B”
1. On all slave server(s)
• mysql> STOP SLAVE IO_THREAD;
• mysql> SHOW SLAVE STATUS;
Wait for value of `Slave_IO_State` to be “Has read all relay log”
• mysql> STOP SLAVE;
2. On “Slave C”
• mysql> CHANGE MASTER TO MASTER_HOST=‘SLAVE_B_IP',
MASTER_USER=‘REPLICATION_USER',
MASTER_PASSWORD=‘REPLICATION_PASSWORD’;
• mysql> START SLAVE;

16. Reverse Failover Steps
If your initial master server is live again and you want to make it master (may be this
server is more powerful in aspect of computing power). You may follow below steps.
1. On all initial master server.
mysql> CHANGE MASTER TO MASTER_HOST=‘CURRENT_MASTER_IP',
MASTER_USER=‘REPLICATION_USER', MASTER_PASSWORD=‘REPLICATION_PASSWORD';
mysql> START SLAVE;
Wait for initial master to update it self.
mysql> Stop Slave;
2. Now you can follow failover steps for initial master server.

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