High availability (HA) is a characteristic of a system that aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. It refers to the ability of a system to operate continuously without failing for a designated period of time. Highly available systems must be well-designed and thoroughly tested before they are used. Planning for one of these systems requires all components to meet the desired availability standard. Data backup and failover capabilities play important roles in ensuring HA systems meet their availability goals. System designers must also pay close attention to the data storage and access technology they use.
High availability requires less human intervention to restore operation in complex systems; the reason for this being that the most common cause for outages is human error. The more complex a system is, the more difficult it is to ensure high availability because there are simply more points of failure in a complex system. High-availability infrastructure is configured to deliver quality performance and handle different loads and failures with minimal or zero downtime. High-availability clusters are servers grouped together to operate as a single, unified system. They share the same storage but use different networks. They also share the same mission, in that they can run the same workloads of the primary system they support.
High-availability software is used to operate high-availability clusters. In a high-availability IT system, there are different layers (physical, data link, network, transport, session, presentation, and application) that have different software needs. At the application layer, for example, load-balancing software is considered critical to help ensure high availability of an application. High-availability software solutions typically provide load balancing and redirecting, automatic application failover, real-time file replication, and automatic failback capabilities.
A highly available system should be able to quickly recover from any sort of failure state to minimize interruptions for the end user. High availability best practices include eliminating single points of failure or any node that would impact the system if it becomes dysfunctional, ensuring all systems and data are backed up for fast and easy recovery, and setting up a system that can quickly recover from any sort of failure state to minimize interruptions for the end user.
High availability is important because downtime results in lost revenue, dec...
