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In this two-part blog series, we will explain the details and functionality of a High Availability (HA) framework for MySQL hosting using MySQL semi-synchronous replication and the Corosync plus Pacemaker stack. In Part I, we’ll walk you through the basics of High Availability, the components of an HA framework, and then introduce you to the HA framework for MySQL. MySQL High Availability Framework Explained – Part I

What is High Availability?

The availability of a computer system is the percentage of time its services are up during a period of time. It’s generally expressed as a series of 9′s. For example, the table below shows availability and the corresponding downtime measured over one year.

The meaning of High Availability varies depending on the requirements of your application and business.  For example, if you cannot afford a downtime of more than a few minutes per year in your service, we say that the service needs to have 99.999% High Availability.

Components of an HA Framework

The essence of being highly available is the ability to instantly recover from failures that can happen in any part of a system. There are four highly essential components in any HA framework that need to work together in an automated fashion to enable this recoverability. Let’s review …

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