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High Availability Cluster

High Availability Cluster

A high availability cluster, also called a failover cluster, will be used to protect one or more business critical applications. To do this, the application and all necessary resources will be continuously checked. To have comprehensive protection of the application, you have to take into account the hardware, network and the operating system required by these processes. Typically, in a lot of different scenarios, customers use protected and unprotected applications on the same node.

High availability cluster solutions which include the opportunity to configure protection for one or more applications are state-of-the-art. With this kind of solution, the crash of one application doesn't require a restart of the complete node, thus interrupting all the other working applications. Depending on the client-side of the application, the last transaction could be lost during a failover.

If the cluster software recognises a failure state, first there will be a local restart of the application. If this isn't successful, the software will initialise a failover to a backup node. The manual process to do this is called a `switch over`. There will not be a local restart in this case.

High availability clusters typically contain a small number of nodes, but there will be the opportunity to use more than 32 or 64 cluster nodes. If a cluster consists of more than two nodes, different failover scenarios will be possible. This could be helpful in reducing the performance reduction after a failover.