How High Availability Works

Techopedia defines High Availability as the systems “that are durable and likely to operate continuously without failure for a long time. The term implies that parts of a system have been fully tested and, in many cases, that there are accommodations for failure in the form of redundant components.”

Simply put, high availability is the ability of the system, website or application to run with maximum potential uptime with little to no downtime. While a more basic system will be sufficient to deliver content to a low or medium number of endpoints, it might include a single point of failure. It means that if downtime occurs in one server due to traffic overload or other concerns, it will bring the entire site or application to a halt. Systems with high availability eliminate this risk by removing single points of failure, which assures the continuous operation in case one component fails.

What High Availability is Not?

However, HA doesn’t mean your site or application will never get downtime. Although it ensures a 99.999% uptime, it is not perfect. Availability is determined by the number of factors, such as configuration settings, and the resources assigned to each component.

Understanding How High Availability Works

There are three critical components of High Availability system:

  • Redundancy
  • Monitoring
  • Failover

Generally, a high availability system works by getting more parts than it requires, running regular checks to overlook the performance of each component, and if one collapses, switching it out for an active system.

Redundancy:

In computing, redundancy is referred to several components that can do the same task. This way, another system can be put to the work if one fails. Because multiple components can perform the same functions, replication is also essential. In a replicated system, the components that do the same tasks coordinate with one another to make sure that they get the same data at all times. For example, you have a (LAMP stack) website hosted on a single Linode. If the database in the LAMP stack fails, PHP might not be able to run queries properly, and your website will not be available to show the requested data or handle user authentication.

In an HA configuration, however, this issue will be minimized as the databases are distributed across several servers. If one of the database servers are not able to process, data can still be handled from one of the others, and since the databases are replicated, any one of them can deliver the same information. Another can replace the collapsed database.

Monitoring and Failover:

In an HA environment, the system is required to overlook itself for problems. This way, regular checks will be done to make sure all components are working efficiently. In failover, a secondary part becomes important when monitoring finds that a primary setup has failed. For example, your database fails, which has made your website out of order. This is because the failed website has no backup to get information. However, even if it had a backup database, the system requires a method to keep track of its failure and to activate the backup for providing information.

In an HA system, the databases are put under regular monitoring to make sure they are working correctly. If there is an error in the results, it means that the primary database is not working, the system fails over. This also indicates the database requests are delivered to a secondary database instead, and because the secondary database has been created to deliver the same data, there is no interruption in the process.

So you must have understood how high availability works. What do you think? Let us know by commenting below.

About Ng Wei Khang

Ng Wei Khang, CEO at a Singapore based IT consultancy company, APIXEL IT Support, has been operational for over 8 years from now. Apixel provides fixed price IT Support Services with unlimited packages that includes small business server setup, Cloud Solution Configuration, Network management and Data security & Theft prevention. The company also provides expert IT consultancy to SMEs in Singapore.

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