High availability refers to a system or component in the OpenSSO Enterprise environment 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. Successful deployments strive for no single point of failure as well as for continuos availability to its users. Different products achieve availability in different ways. For example, clustering is the use of multiple computers to form a single, highly available system. Clustering is often crucial for the Sun Directory Server data store. A clustered multi-master replication (MMR) server pair can increase the availability of each master instance by ensuring availability.
In an OpenSSO Enterprise deployment that meets the minimal requirements, the single points of failure might include:
OpenSSO Enterprise web container
JavaTM Virtual Machine (JVM)
Directory Server hard disk
OpenSSO Enterprise hard disk
Planning for high availability centers around backup and failover processing as well as data storage and access. OpenSSO Enterprise provides session failover and SAML assertion failover functionality. 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. A new application program that has not been thoroughly tested is likely to become a frequent point-of-breakdown in a production system.