High Availability

Deployments strive for no single point of failure (SPOF) as well as continuos availability to its users. Different products achieve availability in different ways; for example, clustering or multi-master replication. The desired high availability refers to a system or component that is continuously operational for a specified length of time. It is generally accomplished with multiple host servers that appear to the user as a single highly available system. In a deployment that meets the minimal requirements (all applications on a single server), the SPOFs might include:

• Access manager web container

• Directory Server

• Java^TM Virtual Machine (JVM)

• Directory Server hard disk

• Access Manager hard disk

• Policy agents

Planning for high availability centers around backup and failover processing as well as data storage and access. For storage, a redundant array of independent disks (RAID) is one approach. For any system to be highly available, the parts of the system should be well-designed and thoroughly tested before they are used. For example, a new application program that has not been thoroughly tested is likely to become a frequent point-of-breakdown in a production system.

Clustering

Clustering is the use of multiple computers to form a single, highly available system. Clustering is often crucial for the Sun Java System Directory Server data store. For example, a clustered multi-master replication (MMR) server pair can increase the availability of each master instance by ensuring availability.