High-Availability Deployment
High-availability deployment is characterized by high load, no external OSS, and a single site with redundancy.
This deployment is very similar to the centralized deployment; the only difference is the use of multiple OSMs (see Figure 34). The OSMs are replicated in different servers to improve the overall availability of the Workflow application. As a bonus, the load can be shared among them.
Like the previous case, an SDX component is the client of the OSMs. The client can issue requests to the various OSMs in a round-robin fashion. For this process to work, each OSM is associated with all workflow engines, each of which reports to a different OSM. With this setup, an engine can be reached through different OSMs, and the load is also shared. If an OSM fails, the reports destined to the OSM are queued in the engine until the OSM comes back up. If an engine fails, the requests are routed to the other OSMs.
Because only one site hosts the Workflow application, the transactional objects in the SDX directory need to be replicated and accessible in only one of the directory servers, the one used by the OSM. For increased availability, you can have more than one directory server. However, you must add directory servers with care so that the additions do not affect the performance of the OSM because of the shadowing agreements of the transactional objects. If you add a directory server, only one server should shadow the transactional objects, the one used by the OSMs. The workflow engines can use all directory servers.
