分散式容錯物件服務之研究

Abstract

分散式物件技術在日益成熟之後，逐漸成為運算模式的主流。而W3C（World Wide Web Consortium）所制定的SOAP（Simple Object Access Protocol）是架構在XML（Extensible Markup Language）之上的分散式溝通協定，具有簡單、開放、標準化等特質。面對廣域網路的異質環境，若要實現分散式物件技術，SOAP會是一個真正跨平台、跨語言的解決方案。在這個新協定中，容錯技術的實作尚無標準，然而處於分散式環境的物件，可能因為主機故障或網路中斷等因素，無法正確運作。為了使系統能有更高的可用度（Availability），必須加入容錯技巧。 SOAP的規格定義中，並無物件註冊與找尋之相關規定，本論文乃提出具有容錯能力之Quorum-based Domain Name Service以實現此機制，並利用SOAP Message達成物件複製（Object Replication）。本系統內之物件皆以SOAP為訊息溝通協定，且已實現主體-備份（Primary-Backup）、動態投票（Dynamic Voting）、Quorum等不同的容錯策略，因此可稱為SOAP-based容錯物件服務平台。所有容錯策略均封裝在基礎類別（Base Class）中，應用物件開發人員可以利用繼承機制使其成果迅速獲得容錯能力。在電子商務領域中，容錯服務有其必要性，因此本平台可以應用於這類資訊系統的設計。最後，本論文實作了股市資訊、郵局帳號管理、聊天室等示範系統，藉以展現容錯平台之能力以及應用物件之實作方法。With the rapid-growing popularity of distributed computing, a simple, open and standard protocol, SOAP (Simple object Access Protocol), over the interoperable environment is indispensable. Based on the technology of XML (Extensible markup language), SOAP will become a new cross-platform and cross-language solution of distributed computing. But, as an innovation standard for distributed computing, the lack of fault-tolerant ability for SOAP will limit its application. In order to increase the availability of business objects, an accretion of fault-tolerant capability on SOAP is essential. Because of the shortage of Naming Service definition in SOAP specification, we propose a fault-tolerant Quorum-based Domain Name Service to meet this requirement. We use SOAP Message to realize object replication and inter-object communication, and then construct a SOAP-based Fault-tolerant Object Service Platform. It comprises base classes of Primary-Backup, Dynamic Voting and Quorum-based object. Taking advantage of object hierarchy, business object developers can build fault-tolerant object easily by inheritance mechanism. In the e-commerce transaction, fault-tolerant service is imperative; therefore our platform is necessary for enterprise-related information systems. We also implement some examples like Stock Quote, Post Office and Chat Room to demonstrate fault-tolerant ability of our platform and the practices of fault-tolerant business object.