1. Dependable Systems (CSE 890), Thursday, 27 th 2003 IRL Interoperable Replication Logic: A three-tier approach to FT-CORBA Infrastructures Authors: R. Baldoni, C. Marchetti, and A. Termini University of Rome “La Sapienza” Presented by: SeyedMasoud Sadjadi A Presentation for CSE 890 Course at Department of Computer Science and Engineering Michigan State University

2. Acknowledgement:  University of Rome “La Sapienza” (IRL) –Roberto Baldoni –Carlo Marchetti –A. Termini  OMG (CORBA)  DOC Group & Lucent Technology (DOORS) –Douglas Smith –Balachandran Natarajan  UCSB & Eternal System Inc. (Eternal) –Lousie Moser –Michael Melliar-Smith –Priya Narasimhan

3. Agenda:  Motivation  Background  IRL Approach  IRL Performance Analysis  Discussion and Concluding Remarks

4. Motivation:  FT-CORBA Limitations: –Interoperability limitations –No support for partitioned systems  Two-Tier Replication Limitations: –Client/Server Synchrony –Thick Client  Support for Legacy CORBA ORBs –Client ORB Transparency

5. IRL Solution:  Introducing Replication Mid-Tier –Separation of Concerns –Supporting Client/Server Asynchrony –Supporting Thin Client (Client Autonomy)  CORBA Portable Interceptors –Legacy Client ORBs Supporting PI can benefit from FT-CORBA –Interoperable Using IIOP

6. Agenda:  Motivation  Background  IRL Approach  IRL Performance Analysis  Discussion and Concluding Remarks

7. CORBA Overview (background)  CORBA is a distribution middleware specification by OMG that –Provides a distributed object computing model. –Hides the communication details, marshalling and un-marshalling.  Elements: –Object, Servant, Server, Client, ORB, ORB, Interface, Stubs, skeletons, DII, DSI, and Object Adapter CORBA Architecture [CORBA-Overview]

8. Fault Tolerance Overview (back. cont.)  Murphy’s Law of Fault Tolerance: –“The only thing that is certain is that the system is going to fail.”  The best that we can do is to –reduce the probability of failure. –but not to zero.  FT-CORBA achieves fault tolerance using: –Entity redundancy –Fault detection –Fault recovery.

9. FT-CORBA Architecture (back. cont.) is_alive() Tutorial on Fault Tolerant CORBA © Eternal Systems, Inc, 2000

10. FT-CORBA Overview (back. cont.)  Redundancy is the basis of fault tolerance  Fault Types: –Processor faults, Network faults, Operating System hangs, Memory leaks, No Software design errors  Object replication –Unit of redundancy in the FT-CORBA  Strong replica consistency –All of the replicas have the same state –Stateless replicas  Not an issue –Stateful replicas  Passive and Active styles of replication.

11. Replication Styles (background cont.) Replication Styles (background cont.)  Passive Replication –Algorithm:  Only one replica processes each request  Other replicas are available as backups if required –Pros and Cons:  Lower memory and processing costs  Slower recovery from faults  Active Replication –Algorithm:  Several replicas process each request –Pros and Cons:  More memory and processing costs  Fastest recovery from faults  Underlying mechanisms are the same for both

12. Active Replication (background cont.) Object Eternal Client invokes a method of Server A Server B Reliable totally ordered multicast STOP Duplicate invocations suppressed Reliable totally ordered multicasts for requests and replies Object Duplicate replies suppressed STOP Tutorial on Fault Tolerant CORBA © Eternal Systems, Inc, 2000

13. Passive Replication (background cont.) Eternal Client invokes a method of Server A Server B Reliable totally ordered multicast Primary replica Primary replica Only primary replica of Server A executes the method Reply returned from primary replica of Server B to primary replica of Server A Only primary replica of Server B executes the method Reliable totally ordered multicast for state transfer Object Tutorial on Fault Tolerant CORBA © Eternal Systems, Inc, 2000

14. Agenda:  Motivation  Background  IRL Approach  IRL Performance Analysis  Discussion and Concluding Remarks

15. IRL Architecture IRL Architecture [IRL] IRL Basic Architecture [IRL] Separation of Concerns Client/Server Asynchrony Client Autonomy Interoperability

16. Replication in IRL TypeComponentStatefulTechnique Host Specific Local Failure Detector Yes Cold Passive IRL FactoryNoStateless Domain Specific Replication Manager YesHot Passive FaultNotifierYesActive ObjectGroup Handler Yes Hot Passive (1) [http://www.dis.uniroma1.it/~irl/details.htm]

17. IRL Deployment  Client-side: –Re-invocation –Re-direction –Req. unique id –Obsolete address  Server-side: –Object replication –Detecting fault –State transfer [IRL]

18. Interoperable Object Group Reference Type_id Number of Profiles IIOP Profile Multiple Components Profile tag_group_ version ft_domain_ id object_group_ id object_group_ version TAG_ INTERNET_IOP Profile Body IIOP Version Host Port Object Key Components Number of Components TAG_GROUP Component TAG_PRIMARY Component Other Components Tutorial on Fault Tolerant CORBA © Eternal Systems, Inc, 2000

19. Three-Tier Replication Protocol Scenario 1 [IRL]

20. Three-Tier Replication Protocol (cont.) Scenario 2 [IRL]

21. Agenda:  Motivation  Background  IRL Approach  IRL Performance Analysis  Discussion and Concluding Remarks

22. Performance Analysis  Testbed: –6 x Intel Pentium II 600 –Windows NT –JDK 1.3.1 –JacORB 1.3.21 –ORBacus 4.1 –10Mbps LAN FN Accuracy [IRL] Minimum percentage increment to apply to LFD heart beating Perfect Fault Detection

23. Performance Analysis (cont.) Experiment Parameters [IRL] Basic Benchmarks [IRL]

24. Performance Analysis (cont.) Stateless Replication Performance [IRL]

25. Performance Analysis (cont.) Stateful Replication Performance [IRL]

26. Performance Analysis (cont.) Stateful Replication Performance: Client Latency [IRL]

27. Performance Analysis (cont.) Percentage Incidence of IRL Components [IRL]

28. Agenda:  Motivation  Background  IRL Approach  IRL Performance Analysis  Discussion and Concluding Remarks

29. Network OS ORB Networ k Application Layer Host Layer Distribution Layer ORB Common Layer Middleware Layers by Schmidt [Taxonomy]  Where are different approaches in the big picture? Domain Layer Eternal TotemIsis Orbix Isis Orbix Eternal Totem IRL DOORS Electra OGS IRL DOORSOGS

30. Concluding Remarks:  Introducing Replication Mid-Tier –Separation of Concerns –Client/Server Asynchrony –Client Autonomy  Using CORBA Portable Interceptors –Legacy Client ORBs Supporting PI can use FT- CORBA –Interoperable Approach Using IIOP –Timeout is not implemented  Portable interceptors are passive

31. References:  [IRL] R. Baldoni, C.Marchetti, A.Termini "Active Software Replication through a Three-tier Approach", in Prooceedings of the 21st Symposium on Reliable Distributed Systems (SRDS'02), pp. 109-118, October 13- 16, 2002 Osaka, Japan.  [CORBA-overview] http://www.cs.wustl.edu/ schmidt/corba- overview.html.  [Taxonomy] D. C. Schmidt, “Middleware for real-time and embedded systems,” Communications of the ACM, vol. 45, June 2002.  [PI] C.Marchetti, L.Verde, and R.Baldoni, “Corba request portable interceptors: A performance analysis,” in the 3nd International Symposium on Distributed Objects and Applications (DOA 2001), (Rome, Italy), Sept. 2001.  [Eternal] L. Moser, P. Melliar-Smith, P. Narasimhan, L. Tewksbury, and V. Kalogeraki, “The eternal system: an architecture for enterprise applications,” in the 3rd International Enterprise Distributed Object Computing Conference (EDOC’99), July 1999.  [CORBA] http://doc.ece.uci.edu/CORBA/formal/02-06-33.pdf