You can implement highly available systems in various ways, and the standard models dictate how the system behaves when a component failure occurs.
The following table summarizes the attributes of the various high availability models. The system recovery time is based on the optimum cluster configuration and varies with the products that are used.
High availability model | Secondary node behavior | Data protection | Failover time |
---|---|---|---|
Load-balanced | Both the primary node and the secondary node are active and they process system requests in parallel. | Data replication is bidirectional and is performed based on the software capabilities. | Zero failover time |
Hot standby | The software component is installed and available on both the primary node and the secondary node. The secondary system is up and running, but it does not process data until the primary node fails. | Data is replicated and both systems contain identical data. Data replication is performed based on the software capabilities. | A few seconds |
Warm standby | The software component is installed and available on the secondary server, which is up and running. If a failure occurs on the primary node, the software components are started on the secondary node. This process is automated by using a cluster manager. | Data is regularly replicated to the secondary system or stored on a shared disk. | A few minutes |
Cold standby | A secondary node acts as the backup for an identical primary system. The secondary node is installed and configured only when the primary node breaks down for the first time. Later, in the event of a primary node failure, the secondary node is powered on and the data is restored while the failed component is restarted. | Data from a primary system can be backed up on a storage system and restored on a secondary system when it is required. | A few hours |
Cluster topologies are classified by the level of high availability that they provide. You can configure the cluster to achieve the level of redundancy you need in case of software or hardware failures. You can introduce cluster management software to reduce system recovery time.