Planning for Change: A Reconfiguration Language for Distributed Systems

In order to help programmers achieve greater leverage of emerging reconfiguration mechanisms, we are studying notations for users to express reconfiguration plans. These plans direct how a running distributed application would be changed, based upon recognition of events from either the application itself or its environment. Our work to date in this area is embodied in a simple system called Clipper. Based upon C++, Clipper provides a way for programmers to express plans, that are then used to automatically generate the run time mechanisms needed to validly reflect the programmer's rules for change in the the application. This paper presents a description of our language in its current form, along with requirements that led up to it. 1 Introduction Reconfiguration of an executing distributed application entails mapping one application state to another. The mapping may be applied to implement a planned upgrade, to recover from a fault condition, or to adjust performance in the applicat..