What are high-availability clusters?
High-availability clusters are servers grouped together to operate as a single, unified system. Also known as failover clusters, 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.
If a server in the cluster fails, another server or node can take over immediately to help ensure the application or service supported by the cluster remains operational. Using high-availability clusters helps ensure there is no single point of failure for critical IT and reduces or eliminates downtime.
High-availability clusters are tested regularly to confirm nodes are always at the ready. IT administrators will often use an open-source heartbeat program to monitor the health of the cluster. The program sends data packets to each machine in a cluster to confirm that it is functioning as intended.
What is high-availability software?
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—which is used to distribute network traffic and application workloads across servers—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.
High availability versus IT disaster recovery?
High-availability IT systems and services are designed to be available 99.999% of the time during both planned and unplanned outages. Known as five nines reliability, the system is essentially always on.
If critical IT infrastructure fails, but is supported by high availability architecture, the backup system or component takes over. This allows users and applications to keep working without disruption and access the same data available before the failure occurred.
IT disaster recovery refers to the policies, tools, and procedures IT organizations must adopt to bring critical IT components and services back online following a catastrophe. An example of an IT disaster is the destruction of a data center due to a natural event like a major earthquake.
Think of high availability as a strategy for managing small but critical failures in IT infrastructure components that can be easily restored. IT disaster recovery is a process for overcoming major events that can sideline entire IT infrastructures.
Both high availability and disaster recovery are important for enhancing business continuity. So, too, is fault tolerance, as described later in this article. Planning for high availability includes identifying the IT systems and services deemed as essential to help ensure business continuity.
