Recovery Guarantees for Internet Applications

Internet-based e-services require application developers to deal explicitly with failures of the underlying software components, e.g. web servers, servlets, browser sessions, etc. This complicates application programming, and may expose failures to end users. This paper presents a framework for an applicationindependent infrastructure that provides recovery guarantees and masks almost all system failures, thus relieving the application programmer from having to deal with these failures, e.g. by making applications stateless. The main concept is an interaction contract between two components regarding message and state preservation. The framework provides comprehensive recovery encompassing data, messages, and the states of application components. We describe techniques to reduce logging cost, allow effective log truncation, and permit independent recovery for critical components. We illustrate the framework's utility via web-based eservices scenarios. Its feasibility is demonstrated by our prototype implementation of interaction contracts based on the Apache web server and the PHP servlet engine. Finally, we discuss industrial relevance for middleware architectures such as .Net or J2EE