[Paper Review] RAFDA: Middleware Supporting the Separation of Application Logic from Distribution Policy

Alan Dearle, Scott Mervyn Walker+3 more|arXiv (Cornell University)|Jun 18, 2010

Distributed and Parallel Computing Systems6 references3 citations

TL;DR

RAFDA is a Java middleware that decouples application logic from distribution policies by enabling dynamic, runtime exposure of any object as a Web Service, supporting per-method, per-parameter transmission policies (by-value or by-reference), and eliminating the need for static interface definitions or code modifications. This enables flexible, late-binding distribution decisions and supports monitoring and management of existing applications without source access.

ABSTRACT

Middleware technologies often limit the way in which object classes may be used in distributed applications due to the fixed distribution policies imposed by the Middleware system. These policies permeate the applications developed using them and force an unnatural encoding of application level semantics. For example, the application programmer has no direct control over inter-address-space parameter passing semantics since it is fixed by the application's distribution topology which is dictated early in the design cycle by the Middleware. This creates applications that are brittle with respect to changes in the way in which the applications are distributed. This paper explores technology permitting arbitrary objects in an application to be dynamically exposed for remote access. Using this, the application can be written without concern for its distribution with object placement and distribution boundaries decided late in the design cycle and even dynamically. Inter-address-space parameter passing semantics may also be decided independently of object implementation and at varying times in the design cycle, again, possibly as late as run-time. Furthermore, transmission policy may be defined on a per-class, per-method or per-parameter basis maximizing plasticity. This flexibility is of utility in the development of new distributed applications and the creation of management and monitoring infrastructures for existing applications.

Motivation & Objective

• To address the brittleness of distributed applications caused by early, static decisions about remote accessibility in middleware systems.
• To eliminate the need for application classes to implement special interfaces or extend special base classes to support remote access.
• To decouple parameter-passing semantics (by-value vs. by-reference) from class implementation and distribution topology.
• To enable late-stage or runtime decisions about object distribution and transmission policies, increasing adaptability and maintainability.
• To support the creation of management and monitoring infrastructures for existing applications without modifying their source code.

Proposed method

• Dynamic deployment of standard Web Services for arbitrary object instances without source code modification.
• Runtime generation and compilation of proxy and stub code using reflection and bytecode manipulation.
• Mapping remote Web Service calls to method invocations on the target object instance via reflection.
• Support for per-method and per-parameter transmission policies (by-value or by-reference), configurable at runtime.
• Integration of smart proxies that cache field values locally to reduce network calls.
• Use of a Remote Reference Technology (RRT) layer to manage remote references and transmission semantics independently of application logic.

Experimental results

Research questions

• RQ1 How can application logic be decoupled from distribution policies in middleware systems to improve flexibility?
• RQ2 Can arbitrary Java objects be dynamically exposed for remote access without source code changes or inheritance constraints?
• RQ3 To what extent can parameter-passing semantics be controlled independently of object distribution and class design?
• RQ4 How can monitoring and management systems be built for existing applications without access to or modification of their source code?
• RQ5 What is the performance and maintainability impact of dynamic, policy-driven remote access compared to static middleware approaches?

Key findings

• RAFDA enables dynamic remote access to any Java object, including compiled and library classes, without requiring changes to their source code or inheritance from special interfaces.
• The system supports per-method and per-parameter transmission policies, allowing fine-grained control over by-value or by-reference semantics at runtime.
• Smart proxies reduce network overhead by caching field values locally, improving performance for frequent accessor calls.
• The framework allows monitoring and management of existing applications without source code access, enabling non-invasive instrumentation.
• The RRT layer decouples distribution decisions from application logic, supporting late-stage or runtime configuration of distribution topology.
• The approach has been successfully applied in a global-scale P2P routing network, supporting both distributed and centralized execution modes without code changes.