High Availability

High Availability (HA) is the ability of a system to operate continuously and error-free over a period of time. The HA ensures that the system achieves the agreed level of operational performance.

SixthStar, we have implemented high availability service for many companies in and around Chennai.

High Availability clusters

  • High availability clusters are grouped servers that act as a unified system. Also called failover clusters, they share the same storage space but use different networks. They also perform the same job as they can run the same workloads as the underlying system they support.
  • If a high availability server in a cluster fails, another ha server or node can immediately take over to keep the cluster-hosted application or service running. Deploying high-availability clusters helps ensure there is no single point of failure for critical computing and reduces or eliminates downtime.
  • HA clusters are regularly tested to ensure nodes are always ready. IT admins often use the open source Heartbeat program to monitor cluster health. The program sends data packets to each machine in the cluster to confirm that it is working as expected.

High availability VS IT disaster recovery?

  • high availability technology IT systems and services are designed to be available 99.999% of the time during planned and unplanned outages. The so-called five-nine reliability system is almost always switched on.
  • If a critical IT infrastructure fails but is supported by a high-availability architecture, the backup system or backup component takes over. This allows users and applications to continue working without interruption and access the same data that was available before the interruption.
  • IT Disaster Recovery refers to the policies, tools, and procedures that IT organizations should adopt to bring critical IT components and services back online after a disaster. An example of a cyber disaster is the destruction of a data center as a result of a natural event, such as a major earthquake.
  • High availability is a strategy for dealing with small but critical failures of IT infrastructure components that can be easily recovered. IT disaster recovery is a process for dealing with serious events that can lead to the failure of the entire IT infrastructure.

Highly Available Load Balancer

  • In general, total availability is expressed as a percentage of availability. A ha load balancer can achieve optimal operational performance by being deployed on a single node or in a cluster.
  • In a single-node deployment, a single ha load balancer performs all management functions and collects and processes all analytics. In a high-availability load-balancing cluster, additional nodes provide node-level redundancy for the load-balancing controller and optimize performance for CPU-intensive scans.

Benefits of high availability

When important business applications and data resources are unavailable, businesses are protected from revenue loss.

The first step in choosing a high availability solution is to completely define the set of availability issues you want to solve. These issues can be grouped into five main groups in terms of business continuity.

1. Planned outages

High availability strategies help mitigate the impact of planned outages. These outages may be necessary for essential maintenance tasks like nightly backups or the installation of new hardware or software. By distributing workloads and services across redundant systems within a high availability cluster, you can ensure that customers and users experience minimal disruption during these maintenance windows.

2. Unplanned outages

High availability solutions provide protection against unforeseen outages caused by human errors, software glitches, hardware failures, and environmental hazards. In the event of a failure on one node or server, the high availability setup, whether for SQL Server, Zimbra HA, or a cloud server, can automatically redirect traffic or workloads to healthy nodes, ensuring uninterrupted service availability.

3. Disaster recovery

Disaster recovery is a critical aspect of high availability. It encompasses a range of tools, strategies, services, and protocols designed to restore and run mission-critical applications and data at a remote location in the event of a catastrophe. High availability configurations, especially those in the cloud, often integrate disaster recovery mechanisms to ensure data and service continuity in the face of disasters.

4. Load balancing

High availability systems can incorporate load balancing mechanisms to optimize resource utilization. Load balancing, whether in the context of SQL Server, Zimbra HA, or cloud servers, involves efficiently distributing tasks or workloads among available resources. This ensures that no single server or node becomes overloaded, enhancing system performance and reliability. In contrast, traditional performance management focuses on allocating resources based on predefined criteria, which may not adapt dynamically to changing demands.

Why is a HA infrastructure necessary?

You require it if...

  • You must regularly deal with important application management.
  • If you manage a website with a lot of traffic,
  • downtime is unaffordable, and service disruptions are your worst nightmare because part of your work involves ensuring high performance.
  • you want a good service that is always accessible.

Elements of high-availability infrastructure


High-availability IT infrastructure features hardware redundancy, software and application redundancy, and data redundancy. Redundancy means the IT components in a high-availability cluster, like servers or high availability database, can perform the same tasks.


Data replication is necessary to achieve high availability. The same nodes in a cluster must exchange and replicate data. To ensure that any node can step in and deliver the best possible service in the event that the high availability web server or network device it is supporting fails, the nodes must interact with one another and share the same information.

In order to help maintain high availability and business continuity in the event that a data centre fails, data can also be copied between clusters.


A high-availability cluster experiences a failover when a task carried out by the failed primary component switches to a backup component. Maintaining an off-site failover system is a best practise for high availability and disaster recovery.

When crucial primary systems fail or become overloaded, IT managers can immediately move traffic to the failover system by keeping an eye on their condition.

Fault Tolerance:

High availability and catastrophe recovery are crucial for business continuity. Together, they aid businesses in developing high levels of fault tolerance, which is the capacity of a system to continue functioning normally even when a number of hardware or software components malfunction.

Low downtime is the goal of high availability compared to fault tolerance's goal of zero downtime. A high-availability system that aims to achieve operational uptime of 99.999%, or five nines, anticipates experiencing 4.61 minutes of downtime annually.

Delivering high-quality performance is not a priority for fault tolerance, in contrast to high availability. To avoid downtime for a mission-critical application, fault-tolerance architecture is used in IT infrastructure.

The cost of fault tolerance is higher than that of high availability Because it can entail backing up entire hardware, software, and power supply systems, fault tolerance is a more expensive method of assuring uptime than high availability. Physical components do not need to be replicated in high-availability systems.

Fault tolerance and high availability work best together because they support IT disaster recovery. The majority of business continuity plans incorporate measures for high availability, fault tolerance, and catastrophe recovery. When an organisation experiences any key IT breakdown, no matter how big or minor, these measures assist in maintaining essential operations and providing support for users.

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