ServerWatch content and product recommendations are editorially independent. We may make money when you click on links to our partners. Learn More.
High availability architecture ensures the operational performance of a system and avoids unplanned downtime and interruptions. In this article, we discuss high availability why it is important, how you measure it, and the best practices.
What Is High Availability?
High availability (HA) refers to the ability of an IT system, component, or application to conform to a high level of operational performance continuously for a specific period without failing. High availability system environments include complex server clusters, as well as the capability to recover the system from unexpected events within the shortest time.
High availability architecture components help to ensure uptime and avoid unplanned downtime and interruptions.
High availability architecture components help to ensure uptime, avoiding unplanned downtime and interruptions. Uptime refers to the system’s reliability to be working and available; conversely, downtime refers to the periods when a system is unavailable.
High availability infrastructure is configured to deliver high-quality performance, handing heavy loads and failures with a minimal rate of downtime. Typically, the availability is represented as the percentage of uptime within a given period.
Why Is High Availability Important?
Availability is the most important aspect of a system. When setting up an IT environment for any kind of organization, high availability must be considered to be the first priority. The organization expects the systems to be available and operational without any interruptions.
If a system is unavailable for unplanned downtime and interruptions, the impact can be huge to the organization or users. For example, Facebook services went down for almost six hours on Oct 4, 2021. The unplanned outage impacted more than 3.5 billion users worldwide and the social media giant lost an estimated $6 billion.
Read more: Top Server Backup Software & Solutions 2021
How Do You measure High Availability?
Availability is calculated by dividing total uptime by the system period (sum of uptime and downtime); the result is multiplied by 100 to get a percentage.
Availability = (Total Uptime System Period)×100
The percentage of availability is sometimes referred to by the number of nines in the digits.
High availability systems and services are designed with the expectation of 99.999% availability during both planned and unplanned outages, known as Five Nines reliability. For reference, Four Nines (99.99%) availability is considered an industry standard. Note that this can vary depending on the systems and their applications.
| Availability | Downtime per day | Downtime per month | Downtime per year |
| One nine (90%) | 2.40 hours | 73.05 hours | 36.53 days |
| Two nines (99%) | 14.40 minutes | 7.31 hours | 3.65 days |
| Three nines (99.9%) | 1.44 minutes | 43.83 minutes | 8.77 hours |
| Four nines (99.99%) | 8.64 seconds | 4.38 minutes | 52.60 minutes |
| Five nines (99.999%) | 864.00 milliseconds | 26.30 seconds | 5.26 minutes |
| Six nines (99.9999%) | 86.40 milliseconds | 2.63 seconds | 31.56 seconds |
High Availability Best Practices
There are various steps to ensure high availability. These best practices help deploy a highly available architecture throughout the enterprise.
Clustering
Clustering can take instant action against the event of a fault in the services. The application services with cluster-awareness can call resources from other servers. When the main server goes down, a secondary server comes in to support. High availability clusters may include multiple nodes that share information.
Backups
One of the most important characteristics of high availability architecture is that data is protected against system failure. Backup and recovery strategy ensures that valuable and sensitive data is stored with proper backup, replication, and recreating capabilities.
Data Synchronization to Meet RPO
Setting data synchronization helps to meet the Recovery Point Objective (RPO) of a system, or “the interval of time that might pass during a disruption before the quantity of data lost during that period exceeds the Business Continuity Plan’s maximum allowable threshold,” according to Druva.
Data Synchronization is the process of establishing consistent data within a system and then continuously updating that data across the system, maintaining data integrity throughout. To achieve the highest availability, the RPO should be set for 60 seconds or less.
Determine RTO
Recovery Time Objective (RTO) refers to the established maximum amount of time to restore business processes to a specific level of service after any disruption or disaster. To achieve Five Nines (99.999%) availability, RTO should be set for 30 seconds or less. It is important to test the target system and ensure it is ready to switch to this model.
Monitoring and Failure Planning
The monitoring tools of a system integrate these services and provide reports on performance. The tools detect ongoing or upcoming disruptions or disasters easily. Failure planning helps the organization take action to increase preparation for the event of a system failure. As such, planning for failure is essential to applying the best practices of high availability.
High availability is the expectation for many services, but sometimes it can be difficult for a company to achieve. That said, there are many providers who support high availability architecture. Every company needs to ensure its services have the highest availability possible, with minimal failure and downtime.
Read next: Best Server Monitoring Software and Tools for 2021
