PHP Failover site / MySQL Failover

CubeXS Weatherly (Pvt) Ltd.

• 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

Index

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

What is Failover?

Replication enables data from one server (the master) to be

replicated to one or more servers (the slaves).

What is Replication?

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

How MySQL Database Replication works?

• 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.

• Analyticslive 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 distributionif 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.

Advantages of MySQL Database Replication

• Unidirectional Replication

• Bi-Directional Replication

• Directed Replication

• Multi Slave Replication

• Circular Replication

Types of MySQL Database Replication

Data is replicated from single master to single slave server, it

involves 2 servers. This setup is usually used for backups.

Unidirectional 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.

Bi-Directional Replication

This setup involves minimum 3 servers, “Server A” being master,

“Server B” and “Server C” being slave to “Server A”.

Multi Slave 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

Directed 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”

Circular Replication

1. Add below directives in MySQL configuration file (my.cnf) and

restart MySQL servicesserver-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 commandmysql> CHANGE MASTER TO MASTER_HOST=‘master_ip',

MASTER_USER='replication_username',

MASTER_PASSWORD='replication_password‘;

mysql> Start Slave;

How to Setup 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.

How to Monitor Replication

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;

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.

Reverse Failover Steps

Thank you

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