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How Service Failures Affect the Siebel Deployment

This topic describes how major architectural components in a Siebel deployment are affected when a service failure occurs. Services include both hardware platforms and software applications.

Web Clients

Client PC hardware failure and browser crashes are the most common causes of Web Client failure. Operating System crashes can also cause this, but are rare. When the Web Client fails, user sessions will be lost even though the sessions usually continue running on the Siebel Server.

This is because when the Web Client fails, the Siebel session cookie usually is also lost. Without the cookie, the user cannot be routed back to the existing user session on the Siebel Server. Therefore, the user will typically need to log in again and start a new user session.

Web Servers

Web servers may fail due to hardware or software issues. Typically, when the Web server fails, Web Clients will not be able to access Siebel Applications, since requests must go through the Web server first. Existing connections from the Web server to Siebel Servers will also be lost.

If Web servers are set up for high availability, for example if there are multiple, load-balanced Web servers, then subsequent requests can be routed to another working Web server. Typically when this occurs, the function of affected Web Client user sessions are not noticeably affected.

Third-Party HTTP Load Balancer for Siebel Servers

Third-party HTTP load balancers handle communication between Web servers and Siebel Servers. Causes of failure differ significantly between hardware-based and software-based solutions. When the load balancer fails, Web Clients and Web servers going through the load balancer will be unable to communicate with Siebel Servers. Network connections in most cases would also be severed, and user sessions will be lost.

If there are multiple, clustered load balancers, then the backup load balancer can take over. Some load balancers can fail over TCP sessions to a backup load balancer. See the vendor's load balancer documentation for details.

When the backup load balancer takes over, user sessions will continue without interruption. However, users sessions will be lost if any of the following occurs:

• A Web Client makes a request while the load balancers are failing over
• TCP sessions are not cleaned up properly on the Web servers

Siebel Servers

Siebel Servers may fail due to hardware or software issues. If the hardware platform fails, or the Siebel Server software fails, then all Siebel Server components will be lost.

In other cases, individual Siebel Server components may fail. This can cause related user sessions or user requests to fail. The major groups of Siebel Server components are as follows:

• Application Object Managers (AOMs). When AOM processes terminate unexpectedly, user sessions hosted by the AOM will be lost. Users must log in to the Siebel application again.

  If users return to the same Siebel Server, SCBroker will attempt to route the user request to a running AOM process.

  If there is only one AOM process and it has failed, then the request will be directed to a different Siebel Server, unless there is only one Siebel Server.

  If AutoStart is enabled, then the Siebel Server process will attempt to restart the terminated AOM process. If successful, the new AOM process will be able to host new user sessions.

• Batch-mode server components going through SRBroker. Most batch-mode server components receive server requests through SRBroker. An example is Workflow Manager. When a batch-mode component fails, the current server request fails:
  • Synchronous server requests. An error will be returned to the requesting component.
  • Asynchronous server requests. An error will be logged but not returned to the requesting component.

    Subsequent requests for the failed batch-mode component will be attempted against either a different instance of the component on the same Siebel Server, or an instance of it on a different server.

    If no instance of the batch-mode component is available, then the request will be logged to the S_SRM_REQUEST table to be processed later.

• Direct Object Manager requests. Examples of direct Object Manager requests are those to Siebel Configurator Object Manager, and communication between AOMs and Report Server. Some of these components, such as Report Server and Configurator, have a native failover mechanism.
• Other server components with location restrictions. There are specialized server components that do not communicate through SRBroker. Siebel Remote Server is an example. Typically, requests to these components can only be processed by a specific Siebel Server. Therefore, if the server fails, requests to that server will fail, until the server is restarted.

Siebel Database

Access to the Siebel Database can fail due to a number of factors:

• Database server hardware failure
• Database server running out of resources
• Disk failure
• Network failure

The impact on the Siebel deployment will be either temporary or long-term. For example, a temporary networking interruption, or a quick database server reboot, would result in a temporary disruption in service. A long-term interruption may occur when there is database corruption or a major server malfunction.

In general, user sessions are lost when there is a Siebel Database service interruption. Users must log in to the system again.

If the interruption is temporary, interactive server components and most of the batch-mode server components attempt to reconnect with the Siebel Database.

If the interruption is long-term, the Siebel deployment must be shut down and restarted once the database service is restored.

Impact of Service Failures

Table 6 summarizes the impact of failure of services in the Siebel deployment. The table includes information on specific services, not already covered.