Choosing Redundancy Strategies for the SunWeb Architecture

The architecture represented in the preceding figure uses two redundancy strategies to meet the quality of service specified for the SunWeb deployment. The two redundancy strategies, load balancing and Directory Server multimaster replication are chosen for the following reasons:

• Load balancing. This solution is preferred for components that do not need to synchronize database updates. Load balancing uses redundant hardware and software components to distribute requests for a service among multiple components instances that provide the service so that no single instance is overloaded. This redundancy also means that if any one instance of a components fails, other instances are available to assume a heavier load. Depending on the latent capacity built into the deployment, a failure might not result in significant degradation of performance. Load balancing is used for several components in the SunWeb architecture, for example, the Portal Server and Access Manager components on sunwebPS1 and sunwebPS2.

• Directory Server multimaster replication. This solution is preferred for Directory Server, which provides data that is crucial to the operation of the entire deployment. Multimaster replication is specifically designed for Directory Server and is therefore relatively easy to implement. The SunWeb architecture uses Directory Server multimaster replication for all the Directory Server instances included in the SunWeb deployment. The SunWeb architecture uses two instances of Directory Server. All eight instances of Access Manager normally connect to the primary Directory Server instance. If the primary Directory Server fails, all eight instances of Access Manager fail over to the secondary Directory Server.