1. Sunday, October 15, 2000 JINI Pattern Language Workshop ACM OOPSLA 2000 Minneapolis, MN, USA Fault Tolerant CORBA Extensions for JINI Pattern Language Aniruddha Gokhale agokhale@lucent.com Bell Labs Research, Lucent Technologies Murray Hill, NJ, USA

2. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 2 Ad hoc Networking Spontaneous network creation i.e., without infrastructure. No additional resources required beyond the participating wireless terminals. Automatic configuration and re-configuration. No specific technical skills needed for network creations and dissolution. Terminals can join and leave the network at anytime. Departure of one terminal does not disrupt communications between other terminals.

3. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 3 Trends in Distributed Systems Distributed applications are becoming more complex & mission-critical Increasing demand for COTS-based multi- dimensional quality-of- service (QoS) support e.g., simultaneous requirements for efficiency, predictability, scalability, security, & dependability Key open challenge is dependable middleware for ad hoc network applications

4. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 4 Promising Solution: Fault Tolerant (FT) Distributed Object Computing Middleware Challenges Limitations of non-OO FT strategies that focus on application processes Techniques based on process- based failure detection & recovery are not applicable to distributed object computing applications due to: 1.Overly coarse granularity 2.Inability to restore complex object relationships 3.Restrictions on process checkpointing & recovery

5. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 5 Solution: Fault Tolerant CORBA Overview Provides a standard set of CORBA interfaces, policies, & services Entity Redundancy of objects is used for fault tolerance via Replication Fault detection & Recovery from failure Features Inter-Operable Group References (IOGR) Replication Manager Fault Detector & Notifier Message Logging for recovery Fault tolerance Domains

6. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 6 Interoperable Object Group References Composite & enhanced Interoperable Object Reference (IOR) for referencing server object groups Comprises one or more TAG_INTERNET_IOP profiles, which in turn must contain a TAG_FT_GROUP and zero or more TAG_IIOP_ALTERNATE_ADDRESS components TAG_PRIMARY component in at most one TAG_INTERNET_IOP profile Client ORBS operate on IOGRs in the same way as with IORs

7. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 7 8.Client sends requests to the primary 2. RM delegates replica creation to local factories 4.The local factories send the replica IOR’s to the RM for it to create the IOGR 5.The RM registers the IOGR with a CORBA Naming Service (NS) 7.Clients contact the NS for IOGR FT-CORBA Component Interaction 1.External object asks RM to set properties for replica group and create it 6.The RM asks fault detectors to initiate fault monitoring of replicas 3.The local factories create CORBA objects

8. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 8 FT CORBA Spec Requirements Preserving the CORBA Object Model with enhancements No single point of failure Transparent failover Transparent client redirection & reinvocation FT CORBA cannot handle commision faults or correlated faults Key Challenge: Support for JINI Pattern Language

9. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 9 Introducing Lease as a FT Property Provide a lease for replica group as a FT Property that can be set as default or at runtime Fault Monitoring and Recovery activated only while lease is valid Failures after lease expiry will throw LeaseExpired exception to the client Better resource management for RM, FD and NS

10. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 10 Adding fallback RM Profile RM’s profile added to the IOGR Profile1Profile2 RM Profile CLIENT ORB Enhanced IOGR Profile Replication Manager Lookup Service LocationForward or ObjectNotFound Client ORB will consult RM profile as a last resort RM will attempt service discovery using service properties Returns new IOGR via LocationForward comprising a new RM profile if found, else throws ObjectNotFound

11. Aniruddha S. GokhaleFault Tolerant CORBA Extensions for JINI 11 Concluding Remarks Current State of the Art COTS-based middleware with multi-dimensional QoS support used to implement dependable distributed systems Key challenges Supporting dependable services in Ad hoc networks Promising Solution FT-CORBA extensions to enhance JINI pattern language Use the Lease pattern in FT-CORBA to manage resources Provide fallback mechanisms that use the Lookup Pattern to rediscover services and provide transparent failover to clients