Service resilience, that is the continued availability of a service despite failures and other negative changes in its environment, is vital in the Service-Oriented Architecture (SOA). A typical way of increasing service resilience is to replicate it. Service replication means deployment of a service on several server machines, each of which may fail independently, and coordination of client interactions with replicas using group communication.

What is RESTGroups?

RESTGroups is a RESTful group communication service which is based on Spread -- a popular group communication toolkit. Spread provides various primitives for:

• detection of malfunctioning/crashed processes,
• reliable point-to-point transfer of messages,
• formation of processes into groups, the structure of which can change at runtime,
• reliable message multicasting with a wide range of guarantees concerning delivery of messages to group members (e.g. causally-, fifo- and totally- ordered message delivery).

RESTGroups functions as an architecture- and language-independent front-end for Spread. Contrary to Spread and many other such systems, RESTGroups represents group communication abstractions as resources on the Web, addressed by URIs. RESTGroups uses methods GET, PUT, POST, and DELETE of HTTP in the RESTful style:

• GET is used to retrieve data (for example, a message) or perform a query on a resource; the data returned from the RESTGroups service is a representation of the requested resource;
• POST is used to create a new resource (for example, to extend a process group with a new process or to send/broadcast a new message); the RESTGroups service may respond with data or a status indicating success or failure.
• PUT is used to update existing resources or data;
• DELETE is used to remove a resource or data (for example, to remove a process from a process group). (In some cases, the update and delete actions may be performed with POST operations as well.)

See a short demo movie explaining the main concepts of group communication and RESTGroups's API to Spread using a small example program.

Distribution

A tarball file with source files is available here:

To deploy demonstration programs you will need the Spread 4.1, available from http://www.spread.org/.

API documentation in HTML format

Team

• Tadeusz Kobus
• Paweł Wojciechowski

Papers

• A 90% RESTful Group Communication Service. Tadeusz Kobus and Paweł T. Wojciechowski.
  In the Proc. of DCDP '10: Workshop on Decentralized Coordination of Distributed Processes, June, 2010.
  An extended abstract appeared in EPTCS volume o n-line. A full version published as Technical Report RA-2/10.
• Koncepcja usługi komunikacji grupowej oraz mechanizmu operacji atomowych dla systemów opartych na paradygmacie SOA (In Polish). Tadeusz Kobus, Mateusz Mor, Paweł T. Wojciechowski. Technical Report TR-ITSOA-OB2-1-PR-09-3, Institute of Computing Science, Poznań University of Technology, May 2009.