High Availability Solutions Overview

High availability solutions for Communications Services vary from product to product.

For example, Messaging Server supports two different high availability solutions, Sun Cluster and Veritas Cluster Server (VCS). Messaging Server provides agents for each of these solutions.

Messaging Server and Calendar Server support different cluster topologies. Refer to the appropriate cluster product documentation for more information.

If you choose to use Application Server as a web container, you can take advantage of its high availability, load balancing, and cluster management capabilities.

Instant Messaging also provides a Sun Cluster agent, but it does not support VCS. You can also create a “more available” deployment by deploying redundant Instant Messaging multiplexors. In such a deployment, if one multiplexor fails, Instant Messaging clients are able to communicate to the back-end server through another available multiplexor.

In addition, you can build in availability to your Communications Services deployment by making infrastructure components, such as Directory Server, highly available.

The following sections in this chapter explain the options available for each component.

Automatic System Reconfiguration (ASR)

In addition to evaluating a purely highly available (HA) solution, you should consider deploying hardware that is capable of ASR.

ASR is a process by which hardware failure related downtime can be minimized. If a server is capable of ASR, it is possible that individual component failures in the hardware result in only minimal downtime. ASR enables the server to reboot itself and configure the failed components out of operation until they can be replaced. The downside is that a failed component that is taken out of service could result in a less performing system. For example, a CPU failure could result in a machine rebooting with fewer CPUs available. A system I/O board or chip failure could result in system with diminished or alternative I/O paths in use.

Different Sun SPARC systems support very different levels of ASR. Some systems support no ASR, while others support very high levels. As a general rule, the more ASR capabilities a server has, the more it costs. In the absence of high availability software, choose machines with a significant amount of hardware redundancy and ASR capability for your data stores, assuming that it is not cost prohibitive.