Application Interface Specification

The Application Interface Specification (AIS) is a collection of open specifications that define the application programming interfaces (APIs) for high-availability application computer software. It is developed and published by the Service Availability Forum (SA Forum) and made freely available. Besides reducing the complexity of high-availability applications and shortening development time, the specifications intended to ease the portability of applications between different middleware implementations and to admit third party developers to a field that was highly proprietary in the past.

The AIS is part of the Service Availability Interfaces (SAI) of the SA Forum. The original specifications, released on April 14, 2003, were the Availability Management Framework (AMF), the Cluster Membership Service (CLM) and four other utility services (Checkpoint, Event, Message, Lock).

Additional services were added in subsequent releases.

AIS consists of 12 services and two frameworks. The services are classified into three functional groups - AIS Platform Services, basic AIS Management Services, and general AIS Utility Services - in addition to the AIS Frameworks.

Initially, the APIs were defined in the C programming language only, but as of July 2008, the Java mapping of the different service APIs is being released incrementally.

The different services and frameworks of the interface specifications have been designed to be modular and, to a certain degree, independent of one another. This allows a system providing only AIS and no HPI to exist and vice versa.

The only required architectural dependency is the dependence on the Cluster Membership Service (CLM). All AIS Services, with the exception of the Platform Management Service (PLM) and the Timer Service (TMR), depend on CLM.

It is expected that all AIS Services should use the AIS Management Services to expose their administrative interfaces, configuration, and runtime management information (fig2).

The Platform Management Service (PLM) provides a logical view of the hardware and the low-level software of the system. Low-level software in this sense comprises the operating system and virtualization layers that provide execution environments for all kinds of software.

The main logical entities implemented by PLM are :

PLM maintains the state of these entities in the information model and provides means to control them and track any state changes. To fulfill these tasks for HEs, the PLM Service typically uses HPI. In case of EEs, PLM is in charge of retrieving all necessary information about the health of the operating system and any available virtualization layer.

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