Experience in Implementing an HTTP Service Closure

One ideal of configuration management is to specify only desired behavior in a high-level language, while an automatic configuration management system assures that behavior on an ongoing basis. We call a self-managing subsystem of this kind a closure. To better understand the nature of closures, we implemented an HTTP service closure on top of an Apache web server. While the procedure for building the server is imperative in nature, and the configuration language for the original server is declarative, the language for the closure must be transactional; i.e., based upon predictable and verifiable atomic changes in behavioral state. We study the desirable properties of such transactional configuration management languages, and conclude that these languages may well be the key to solving the change management problem for network configuration management.