Business tier patterns

This section describes the business tier solution patterns and their impact on NFRs.

Active/Passive clustering

This pattern warrants that the system as a whole continues to function if part(s) of the system go offline.

Context

Architecting an n-tier architecture where high availability is one of the prime non-functional requirements.

Drivers

Drivers for the active/passive solution pattern include:

• The system has a required level of availability which must be delivered even in the face of hardware or software failure.
• The system has to be maintained and upgraded over time. Even with planned downtime, there may be a need to upgrade or fix a system element whilst ensuring the system remains available.

Solution

Provide alternative capacity for your critical system elements by duplicating those elements. Redirect users to the duplicate should the active element become unavailable.

This pattern must be applied equally to hardware and software. Software elements are, perhaps, more prone...