Siebel Deployment Planning Guide > High Availability Deployment Planning >

About High Availability Deployment Options

High availability means that a user can access key system services even when the underlying hardware or software for those services fails. For example, if a user synchronization session was interrupted by a failure of the server computer to which it was connected, then the user can reconnect to a Siebel Remote Server and restart the synchronization process without any data loss.

To achieve high availability, the overall system must automatically replace lost services and distribute loads among services to assure acceptable response times. When a lost service cannot be replaced automatically, this is called a single point of failure. High availability planning and deployment are designed to eliminate these single points of failure.

In a Siebel Business Applications deployment, a service (for the purposes of this discussion) is one of the following:

• Siebel Gateway Name Server
• Siebel Server
• Siebel database
• Siebel File System
• Web server with the Siebel Web Server Extension (SWSE) installed

To eliminate single points of failure, some form of redundancy is required. Clustered servers are an example. When one service fails, other resources are available to take over for the failed service. To be successful, this process must be:

• Automatic: No operator intervention is necessary
• Transparent: Users do not have to change anything for the services that have failover protection

There are cases where full, automatic failover might not be possible. For example, results of the failure might have to be manually cleaned up. This guide does not cover all of the possible cases, and customers are advised to review environment-specific requirements before finalizing high availability planning.

The options available for high availability deployment consist of the following techniques:

• Scalable services (load balancing)
• Resilient processing (distributed services)
• Server clusters

Scalable Services (Load Balancing)

Load balancing distributes workload across multiple servers. Each server runs an instance of the service that you want to load-balance. Load balancing also provides failover. If one server fails, then requests are automatically routed to the remaining servers.

Application Object Managers are the server components for which load balancing is most frequently provided. Distributing workload across Application Object Managers indirectly distributes workload across the other server components that Application Object Managers call, in a form of indirect load balancing.

Resilient Processing (Distributed Services)

Resilient processing, also called distributed services, is used for tasks initiated by the Siebel Server. (Load balancing is used for tasks initiated by users.) Multiple instances of a component run on the same Siebel Server, or the same component can run on multiple Siebel Servers. If one instance of the component fails, then another instance on the same server or on a different server takes over processing subsequent requests. For more information, see About Resilient Processing.

Server Clusters

Server clusters consist of two or more physical servers linked together so that, if one server fails, then resources such as physical disks, network addresses, and applications can be switched over to the other server. Server clusters can provide resilience when a particular Siebel operation can only take place on one server, either because of the type of process (such as Siebel Gateway Name Server or Siebel Remote) or because of hardware constraints.

Figure 5 illustrates an example of server load balancing and server clustering in a Siebel Enterprise Server.

Figure 5. Example of a High Availability Deployment