Host Application Software
3.3.2Graceful Switchover
In a Redundant Host environment a graceful switchover is only secondary in importance to data integrity. An effective mechanism is required in order for an application to seamlessly pick up the functionality of a faulted application. The Intel Redundant Host environment has an infrastructure in place to help facilitate such control transitions. This architecture supplies:
•Multiple communication paths
•A capable fault detection interface
•Embedded firmware that can be configured for multiple failover scenarios
In addition to providing a fine level of granularity on the type of switchovers provided, this platform also exposes these switchover events to an application or platform interface module so that the software can act upon the events appropriately.
3.3.3Hardened Applications
In almost all environments it is important to develop applications in a hardened manner, but in a highly available embedded environment it is especially important. The definition of the term “Hardened” may vary depending on the type of system that is being developed and the accessibility of various system level software components. In the context of this Redundant Host architecture, the term hardened refers to verifying that all function return codes are appropriately handled and dispatched with accordingly, function parameters are validated, and that the system maintains a logging mechanism sufficient to monitor system performance and to assist in diagnosing fault conditions when present. Code hardening should be part of any standard development effort, but a disciplined approach to code hardening must be maintained in an HA environment.
3.3.4Code Modularity
Code modularity is also considered a common implementation characteristic, but it is often overlooked during the implementation portion of a project. In order to achieve some level of application portability the designers need to make the conscience effort to move away from typical embedded monolithic designs.
One approach to modular design in an HA architecture is to decouple the services provided by the system from the entities responsible for system management. Since system management is heavily dependant on the hardware configuration of the host platform, the implementation of a platform interface module helps to abstract the host application away from the platform on which it resides. The Platform Interface Module achieves platform abstraction by handling most hardware level monitoring and exposing platform specific interfaces only through
24 | High Availability Software for the Intel® NetStructureTM ZT 4901 Technical Product Specification |
