1. A Software Architecture for Translucent Replication Etienne Antoniutti Di Muro Università degli Studi di Trieste, Italy eantoniutti@units.it 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France

2. Directions… Arjuna Technologies Ltd. Newcastle upon Tyne, UK > Stuart Wheater (co-supervisor ) Università degli Studi di Trieste > Etienne Antoniutti Di Muro > Prof. Alberto Bartoli (supervisor ) 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 29th November 2005 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 2/23

3. Food for thought… > Background and motivations: > Middleware transparency, crisis and paradox > Dependability vs. performance > Goal: Address dependability and performance conflicts > Proposal: Translucent replication: > top-down and bottom-up translucency models > application requirements > Evaluation: Translucent replication in a real case scenario > JMS translucent replication > Summary and Conclusions 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 3/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

4. Background and motivations: > to provide a common high-level environment to the components of a distributed system > to isolate applications form underlying hw/sw changes distributed application(s) > < operating system hardware > < MIDDLEWARE > < Application(s) Domain Specific Services Host-infrastructure Services Common Services Distribution Services System Platform network Application(s) Domain Specific Services Host-infrastructure Services Common services Distribution Services System Platform > Middleware: born TRANPARENT and HOMOGENEOUS … 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 4/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

5. Background and motivations: > Middleware: …grown MONOLITHIC and HETEROGENEOUS > to achieve transparency > to accommodate application complexity, distribution models, (COTS) component reuse > Middleware: requires a partial redesign to match the exact application requirements: the middleware crisis > Middleware: faces an interoperability problem coming from middleware itself: the middleware paradox 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 5/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

6. interlude: clustering and replication > Clustering : exploiting services using multiple physical machines w/ external appearance of one single highly capable server > performance > Replication : having a service replicated across multiple nodes ensures that another instance of the service exists if one replica crashes > service dependability, i.e. availability and reliability Service Clients network 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 6/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

7. > Clustering and Replication : a common requirement is replication transparency: neither clients nor applications should have to be aware of multiple physical data replicas > Example: > ADAPT (Middleware Technologies for Adaptive and Composable Distributed Components). EU contract no. IST-2001-37126 (2005) > no interaction between the replicated beans and the replication layer across the application/middleware boundary 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 7/23 Bean ADAPT Framework Replication Algorithm J2EE Server Communication with other replicas A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro Application/middleware boundary

8. interlude: clustering and replication > Example: > A Replication Framework for Program-to-Program Interaction across Unreliable Networks and its Implementation in a Servlet Container (2004) > no interaction between the replicated web service and the replication layer across the application/middleware boundary 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 8/23 Web Service Servlet Container Replication Layer Replication Algorithm Client Interceptor Communication with other replicas A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro application/middleware boundary

9. Background and motivations: > Dependability and performance conflicts: > dependability: long-standing desirable property > efficient replication remains challenging > Maintaining high performance figures while ensuring strong consistency presents a tough contest > Replication transparency leads to under-utilization of resources with resulting poor application performance 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 9/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

10. Goal: > Address system dependability and performance conflicts introducing Middleware Translucency > New software architectural model > Middleware layers interfaces and interactions are exposed to the system designers: > transparently to the application that want it > with the desired level of granularity to the applications that need it > Dependability and performance conflicts have to become trade-offs > Trade-offs offer sets of solutions for the dependability/performance conflicts in the application design space 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 10/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

11. Goal: > Novel translucency models: > top-down : upper layers provide information to lower layers about how they want their requests to be satisfied > bottom-up : lower layers provide information to upper layers about how they are performing their work and the computational environment, so that upper layers can adapt their behavior > Strong cross-layer interaction > Dynamical adaptability of middleware layers > Middleware high configurability to application requirements 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 11/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

12. Proposal: > Translucent Replication: > novel architecture for replicated infrastructures > decomposition of system level clustering requirements into lower level functional requirements > layered services realize functional requirements 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 12/23 distributed application(s) > REPLICATION MIDDLEWARE network Application(s) System Platform Context Service Communication Service Persistence Service Service State Custom Service(s) > operating system hardware > A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

13. Proposal: > Translucent Replication: > Top-down and bottom-up model 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 13/23 distributed application(s) > REPLICATION MIDDLEWARE > > Semantic Rules (Custom) Sensors API < top-down translucency model components < bottom-up translucency model components < replicated data path < top-down translucency model information path < bottom-up translucency model information path Single Replica network Application(s) System platform Context Service (GC) Communication Service Persistence Service Service State Custom Service(s) Knowledge Repository < < < A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro application/middleware boundary operating system hardware >

14. Proposal: > Translucent Replication: reasoning on data semantics > generic way to implement smart replication middleware > provides the finest level of granularity for data handling > deals with replication of a wide range of entities: > i.e. raw and plain data / objects / components > no need to develop specific different patterns > Application requirements > formal description of operation and data semantics > messages sent to the middleware in a clear an fixed format >Designers / Programmers > define rules to enable data semantics access > define sensors to monitor resources for application-specific adaptation 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 14/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

15. Evaluation: > Translucent Replication model evaluation : tricky > put in numbers the advantages of solutions based on data semantics > flexibility and adaptability of a middleware architecture to specific application dependability solutions > different levels of granularity: explosion of the number of possible tunable parameters > solutions in a multidimensional space > providing translucent methodologies to application design is a trade-off itself > Model application evaluation > Real case scenario evaluation 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 15/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

16. network System platform Context Service (GC) Communication ServicePersistence ServiceService StateKnowledge Repository Evaluation: > Model application evaluation 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 16/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro application Application Data < Data-specific API interaction < Data-specific rules< > Application throughput and latency comparison with a combination of different data Platform basic sensors < < ‘opaque’ data class < data class

17. > JMS specs: put high demands on the message server > JMS specs: rich semantics, represent different types of messaging > JMS clustering model : shared persistent store interlude: JMS clustering 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 17/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro JMS Primary Server JMS Backup Server 1 Shared persistent store Prod. Cons. JMS Backup Server 2 > not continuous availability > idle servers: waste of hardware resources

18. > JMS clustering model: back channel interlude: JMS clustering 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 18/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro > redundant networking > complex system architecture > waste of hardware resources JMS Backup Server 1 Back channel Prod. Cons. JMS Primary Server JMS Backup Server 2

19. Evaluation: > JMS translucent clustering evaluation > JMS cluster based on group communication > provides high levels of data redundancy > translucency fits JMS rich semantics: > i.e. producers / consumers requests > i.e. persistent / non persistent messages > functional homogeneity JMS cluster design > ‘Blind’ replication test-bed (comparison baseline) > JMS Server clients throughput and latency for different levels of translucency > Scalability: destination, throughput, connections … > 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 19/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

20. Summary >Transparent middleware approach: important issue >Dependability vs. performance conflicts >Transparent replication >Translucent architecture: top-down and bottom-up models >Novel translucent replication architecture >Evaluation: model application and real case scenario 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 20/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

21. Conclusions 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 21/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro >Translucent middleware > offers appropriate programming interface elements to the application >pluggable modules (semantic rules) can be defined to expose the required level of granularity >pluggable sensor can be defined for encapsulating management resources >cross-layer interactions >access middleware machinery according to application-specific requirements >adjust the conflicts between dependability and performance turning them into trade-offs >provide sets of solutions for application dependabiliy/performance trade-offs

22. Questions ? 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 22/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro

23. Thank you! 29th November, 2005 2nd Middleware Doctoral Symposium @ Middleware 2005 Conference, Grenoble, France 23/23 A Software Architecture for Translucent Replication : Etienne Antoniutti Di Muro