MySQL High Availability and Replication: A Complete Guide

on Database, Database Management Systems, MySQL, Relational Database • April 20th, 2022 • Write for Hevo

MySQL High Availability- Featured Image

Every organization often uses a variety of business-critical databases and applications, such as Data Warehouses, Customer Relationship Management (CRM) Systems, E-commerce & Supply Chain Management Applications, and Financial & Business Intelligence Systems for enhancing business growth. When a system, database, or application fails in unusual circumstances, firms may face significant revenue loss, unproductive staff, and unsatisfied consumers. 

According to Enterprise Server Downtime Worldwide Report (2019) from Statista, 40% of respondents said that a single hour of downtime costs their company more than USD 1 million of revenue loss. In order to ensure zero or less downtime, organizations have to implement High Availability (HA) frameworks for databases like MySQL high availability to provide persistent availability in case of failures. 

In this article, you will learn about MySQL high availability framework, the features of MySQL high availability framework, and how MySQL achieves high availability using the MySQL InnoDB cluster.

Table of Contents

Prerequisites

A fundamental understanding of data redundancy techniques and MySQL databases.

What is MySQL?

MySQL Logo: MySQL High Availability I Hevo Data
Image Source: Vector Logo Zone

Developed in 1995, MySQL is one of the most popular Relational Database Management Systems (RDBMS) that allows you to store, manage, and process data stored in databases or servers. In other words, MySQL is the open-source RDBMS that enables you to store, manage, and query colossal amounts of data using a Structured Query Language (SQL). 

With MySQL, you can implement various Data Processing techniques like Data Filtering, Data Manipulation, Aggregation, Joining, and Wrangling. In addition, MySQL is compatible with a wide range of operating systems, including Windows, macOS, and Linux, and it supports a variety of programming languages, including PHP, PERL, C, C++, JAVA, and others.

To discover the differences between PostgreSQL and MySQL, visit our in-depth guide on PostgreSQL vs MySQL: 8 Critical Differences.

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What is High Availability?

High availability (HA) refers to a system’s capacity to operate continuously without failure for a prolonged period of time. The HA framework works to verify that a system meets the user requirements without any interruption in end-to-end data processing, thereby ensuring fault tolerance and high data availability. 

In other terms, high availability (HA) is a technique that eliminates a single point or accidental failure of systems or applications to assure continuous operations or uptime for an extended period of time. The percentage of time a computer system’s services are available over a given period of time is referred to as its availability or high availability. It is commonly expressed as a succession of 9′s. 

The high availability percentage will vary depending on your system or application. For example, four 9s,’ i.e., 99.99 % availability, is an industry standard for mission-critical applications such as your E-commerce and Financial Service Systems. You can expect no more than 52.60 minutes of outage per year or 8.64 seconds of downtime per day if your system is 99.99 percent available. 

Similarly, for non-critical applications and systems, high availability may be a two 9s, i.e., 99%, equating to 8.77 hours of downtime per year or 1.44 minutes of unavailability per day. According to industry standards, if the system or application cannot afford more than a few minutes of outage per year, it is evident that the service requires 99.999 percent of High Availability.

The table below displays the availability and the corresponding downtime throughout the year.

High Availability Table: MySQL High Availability I Hevo Data
Image Source: ScaleGrid

Features of High Availability Framework

The ability to recover instantly from faults that can occur in any component of a system is the foundation of being a highly available system. To ensure recoverability and high availability, four critical components in any HA system must work together in an automated method. 

1. Infrastructure and Data Redundancy

To ensure that a service is highly available, we must ensure that the infrastructure hosting it has redundancy as well as an up-to-date redundant copy of the data that the service consumes or offers. This serves as a backup service, ready to take over if failures disrupt the primary or main database.

2. Failure Detection & Correction Mechanism

It is critical to notice any faults in any aspect of the core system that may impair its availability as soon as possible. This will allow the framework to either perform corrective steps on the primary system or failover the services to a standby system.

3. Failover Mechanism

This component is in charge of transferring services to your backup infrastructure. Users should ensure that if numerous redundant systems are available, this failover mechanism component must choose the best one and promote it as the primary service.

4. User/Application Redirection Mechanism

When the standby systems take over as the primary, the high availability feature guarantees that all application and user connections are transferred or redirected to the new primary database. In the context of MySQL databases, more will be discovered in the upcoming sections of MySQL high availability.

5. Continuous Running

When a system or application runs continuously, even a single or short outage can cause considerably larger difficulties as connected, and synchronized systems fail in a cascade. In such scenarios, it is worthwhile to consider investing in high availability, since the costs of system or application repairs are significantly higher.

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MySQL High Availability Framework

The below-given image resembles the framework for implementing optimal MySQL high availability and data redundancy.

MySQL High Availability Framework: MySQL High Availability I Hevo Data
Image Source: ScaleGrid

In the MySQL high availability framework, a Three-Node Master-Slave Configuration is used for implementing MySQL semi-synchronous replication process, assuring infrastructure and data redundancy. In addition, the Corosync and Pacemaker components are utilized for failure detection and rectification.

Let’s take a closer look at the functionality of some of the key components of the MySQL high availability framework.

1. Corosync

The first component of MySQL high availability framework, Corosync, provides a transparent communication infrastructure for the database servers or nodes, allowing them to exchange messages reliably. It creates a cluster ring of nodes and maintains track of which nodes join and leave the cluster via cluster membership.

Corosync also collaborates closely with the Pacemaker component to transmit node availability so that the Pacemaker can make informed judgments.

2. Pacemaker

The Pacemaker is a fundamental component of the MySQL high availability infrastructure, ensuring high availability for MySQL databases running on the cluster. It is also known as Cluster Resource Manager (CRM) since it identifies and addresses node-level failures by interfacing with Corosync.

Pacemaker not only detects node-level failures but also detects and solves MySQL errors by interacting with the Resource Agent (RA) component. Furthermore, Pacemaker configures and controls the MySQL resource by performing activities such as start, stop, monitor, promote, and demote. 

3. Resource Agent 

This MySQL high availability component, i.e. the Resource Agent, serves as a conduit or interface between MySQL master-slave databases and Pacemaker. It is mainly used to implement start, stop, promote, demote, and monitor actions that are initiated by the Pacemaker. 

4. DNS Mapping Component

After a successful failover, the Resource Agent executes the DNS Mapping Component, which changes the master MySQL server’s DNS records with the IP address of the new master. In addition, clients always connect to the MySQL server using a master DNS name. 

By maintaining the mapping of this DNS name to the IP address of the existing master database, users can ensure that clients do not need to update their connection strings or properties when there is a failover.

How Does MySQL Achieve High Availability?

To achieve MySQL high availability and data redundancy, the MySQL database uses the MySQL InnoDB cluster. The MySQL InnoDB cluster provides an integrated and native HA solution for your databases, with single and multi-master failover detection capabilities. The MySQL InnoDB cluster consists of three main components such as MySQL Servers with Group Replication capabilities, MySQL Router, and MySQL Shell. 

1. MySQL Servers with Group Replication Capabilities

MySQL Servers with Group Replication capabilities ensure MySQL high availability by replicating data to all cluster members and providing fault tolerance, automated failover, and elasticity. It is the collection of database servers that replicates MySQL databases across several nodes, ensuring fault tolerance and data availability. 

When data in the MySQL databases changes, it immediately replicates to the server’s secondary nodes. The MySQL Group Replication idea is comparable to the AlwaysOn availability group concept.

2. MySQL Router

The MySQL Router concept is similar to the Windows Server failover cluster’s virtual network name. When a failover occurs, the client application must always be aware of the PRIMARY instance and cluster topology, where this functionality is handled by the MySQL Router. It directs data requests to the nearest MySQL Server instance that is available. In addition, MySQL Router acts as a proxy to hide the multiple MySQL database servers.

3. MySQL Shell

MySQL Shell is a configuration utility for connecting, deploying, and managing the MySQL InnoDB cluster. MySQL Shell includes an Admin API, which contains a dba global variable to initialize the corresponding session variables for new connections to MySQL. With MySQL Shell, the InnoDB cluster can be deployed and managed using the dba variable.

MySQL InnoDB Cluster combines MySQL Server with Group Replication, MySQL Router, and MySQL Shell, eliminating the need for third-party tools, scripts, or other components. Furthermore, it uses tried-and-true MySQL capabilities such as InnoDB, GTIDs, binary logs, multi-threaded replication, multi-source replication, and performance schema. It only takes less than five minutes to set up a MySQL InnoDB Cluster, which may be further controlled via the MySQL Shell’s scriptable Admin API.

Conclusion

In this article, you learned about MySQL, the high availability (HA) framework, MySQL high availability framework, features of the MySQL high availability framework, and the mechanism of how MySQL achieves high availability. As the next step, you can explore and learn how to implement the deployment process in MySQL for achieving high availability in MySQL databases. To learn more about MySQL’s high availability, you can check their official documentation.

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