Fault tolerant Web Services

Zwass suggested that middleware and message service is one of the five fundamental technologies used to realize Electronic Commerce (EC). The Simple Object Access Protocol (SOAP) is recognized as a more promising middleware for EC applications among other leading candidates such as CORBA. Many recent polls reveal however that security and reliability issues are major concerns that discourage people from engaging in EC transactions. We notice that the fault-tolerance issue is somewhat neglected in the current standard, i.e., SOAP 1.2. We therefore propose a fault tolerant Web Services called fault tolerant SOAP or FT-SOAP through which Web Services can be built with higher resilience to failure. FT-SOAP is based on our previous experience with an object fault tolerant service (OFS) and OMG's fault tolerant CORBA (FT-CORBA). There are many architectural differences between SOAP and CORBA. One of the major contributions of this work is to discuss the impact of these architectural differences on FT-SOAP design. Our experience shows that Web Services built on a SOAP framework enjoy higher flexibility compared to those built on CORBA. We also point out the limitations of the current feature sets of SOAP 1.2, e.g. the application of the intermediary. In addition, we examine two implementation approaches; namely, one based on the SOAP 1.2's intermediary, and the other on Axis handler. We conclude that the intermediary approach is infeasible due to the backward compatibility issue. We believe our experience is valuable not only to the fault-tolerance community, but also to other communities as well, in particular, to those who are familiar with the CORBA platform.