High availability cluster definition
A high availability (HA) cluster ensures that a system remains available and operational with minimal downtime, even in the event of hardware or software failures. This setup is crucial for services where continuous operation is essential, like banks, hospitals, or data centers.
See also: database clustering, cluster analysis, cluster controller, node
Here’s how it works:
- Redundancy. At the heart of an HA cluster is the principle of redundancy. The cluster consists of two or more nodes that are set up to perform the same tasks. This means that if one node fails, another can take over its duties without interruption to the service. The nodes share access to data to ensure they can all provide the same services.
- Monitoring. HA clusters continuously monitor the status of each node to detect failures as soon as they happen. This monitoring includes the health of the hardware, the status of applications, and network connectivity. If a problem is detected, the cluster management software takes action to mitigate the issue.
- Failover. Failover is the process of switching operations from the failed node to a standby node. When the cluster management software detects a failure, it automatically reassigns the tasks of the failed node to another node in the cluster. The failover process is designed to be quick to minimize downtime and ensure continuous service availability.
- Load balancing. Some HA clusters also implement load balancing, distributing the incoming requests or workload evenly across all nodes. This prevents any single node from becoming a bottleneck and improves the overall performance and reliability of the service.
- Synchronization. To ensure that all nodes can take over from one another at any time, data and configurations are kept synchronized across the cluster. This synchronization ensures that a failover node can immediately provide the same services as the node it replaces, using the most current data.
- Cluster management software. The operation of an HA cluster is overseen by cluster management software. This software orchestrates monitoring, failover, load balancing, and synchronization. It makes decisions about when to initiate a failover and which node should take over services based on predefined policies and the current state of the cluster.
