Group Service in CORBA

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Group Service in CORBA

• Xing Gang
• Supervisor Prof. Michael R. Lyu
• Marker Prof. Irwin K. C. King, Prof. John C.
  S. Lui

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Outline

• Motivation
• Background
• Group Service
• Group-based System
• Group Communication in CORBA
• CORBA FT Service
• OmniORB
• Proposed System
• Schedule

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Motivation

• Goal
• Provide Fault Tolerance via Entity Redundancy
• Use Group Service to Manage the Redundant Entity
• Group Service Provide Reliable Group
  Communication (multicast)
• CORBA FT Service Specification

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Idea of Group Communication

• Group Communication is to gather a set of
  processes or objects into a logical group, and to
  provide primitives for sending messages to all
  group members at the same time with various
  ordering guarantees

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Total Order Multicast
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Active Replication
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Primary-Backup Replication
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Group-Base System

• Isis
• Horus
• Ensemble (Maestro) Cornell Univ.
• Totem UCSB
• Transis Hebrew Univ.
• Phoenix Swiss FIT

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Different Approaches

• Integration Approach integrates an existing
  group communication system within an ORB
• Interception Approach intercepts messages
  issued by an ORB and maps them to a group
  communication toolkit
• Service Approach provides group communication
  as a CORBA service beside the ORB

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Integration Approach
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OrbixIsis
Orbix
Client
Isis
Server1
Server2
Server3
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Interception Approach
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Eternal
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Service Approach
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OGS
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Approaches Comparison
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CORBA FT Service(1)

• Time Line
• RFP Issued -- April 1998
• Initial Proposals Submitted -- October 1998
• Joint Revised Submission -- October 1999
• Approved by OMG December 1999
• Objective
• Wide range of fault tolerance
• Simple low-cost clients
• Highly reliable servers
• Passive and Active replication
• Both automatic and application-controlled fault
  tolerance mechanisms
• Strong replica consistency, when needed

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CORBA FT Service(2)

• Fault Tolerance Properties
• Replication Styles
• Infrastructure-Controlled and Application-Controll
  ed
• Object Group References and Alternative
  Destinations
• At-Most-Once Invocation
• Fault Detection and Notification
• Checkpointing and Logging

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Architectural Overview
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omniORB

• omniORB is a robust, high-performance CORBA 2
  ORB, developed by ATT Labs research
• omniORB is freely available under GPL
• Feathers
• C binding
• Native IIOP
• Multithread
• Naming and Lifecycle Service
• omniORB3

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Add Group Service to omniORB

• Objective
• Robustness
• Completeness
• Performance

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ORB Multicasting

• Enhance POA to provide group management interface
  to ORB
• Multicast Algorithms (protocol)
• Isis/Hours/Ensemble
• Totem
• Transis
• Semiotics
• at least once
• at most once
• exactly once

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Assumptions

• No Low Level Group Communication Toolkit
• NO IP Multicast
• No Network Partition Problem
• Higher Level Group Management Service
• Use CORBA FT Service Interface

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Active Replication

• Requirement
• Group Management (ATT)
• Multicast Implementation
• Fault Tolerance Service Spec. Compliance

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Experimentation Evaluation

• Application
• Active Replicate Name Server
• Evaluation of Current Specification
• Discovery
• Overhead
• Reliability

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Schedule

• Multicast Protocol
• August 31,2000
• Integrate with ATT Group Management Service
• November 30,2000
• Applications Evaluation
• March 31,2000

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QA
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Thank You!!