24 High Availability Software for the Intel® NetStructureTM ZT 4901 Technical Product Specification
Host Application Software
3.3.2 Graceful 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.
3.3.3 Hardened 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.
3.3.4 Code 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 non-proprietary APIs. One of
the advantages of the Intel High Availability Redundant Host System is the reliance on industry-
standard, non-proprietary interfaces. These interfaces allow for future portability of the developed
code base.