System models in distributed system
- 1. System Models • Threatsto consider for modeling - Widely varying modes of use: component parts are subject to wide variations in workload. - Wide range of system environments: Able to accommodate heterogenous h/w, s/w, OS etc. - Internal problems: Failures, inconsistency of data etc - External threats: Attack on data integrity. • Types - Physical - Architectural - Fundamental Isha Padhy, Department of CSE, CBIT, Hyderabad 1
- 2. Physical Model • Modelthat capture the hardware composition of a system in terms of computer and their interconnecting networks. • Three generations of distributed systems: –Early distributed systems –Internet-scale distributed systems: CORBA –Contemporary distributed systems Isha Padhy, Department of CSE, CBIT, Hyderabad 2
- 3. Architectural Model • Architecture:The structure of a system specifying its components and their interrelationships. • Why architecture? – To ensure that the structure will meet the current and future demands on it – To provide a reliable, manageable, adaptable and cost-effective system(MARC) • Ways of organization of DS - Software Architecture - System ArchitectureIsha Padhy, Department of CSE, CBIT, Hyderabad 3
- 4. Architectural model • Architecturalelements: How to understand the fundamental building blocks of a distributed system? • What are the entities that are communicating in the distributed system (communicating entities)? • How do they communicate, or, what communication paradigm is used (communication paradigms)? • What roles and responsibilities do they have in the overall architecture (roles and responsibilities)? • How do they map on to the physical distributed architecture (what is their placement)? Isha Padhy, Department of CSE, CBIT, Hyderabad 4
- 5. Architectural elements • Communicatingentities: Entities that take part - Processes - Objects - Components - Web services Isha Padhy, Department of CSE, CBIT, Hyderabad 5
- 6. Architectural Elements Communication paradigms:How they communicate Inter-process communication – low-level process support. E.g. message passing primitives, direct access to API, multicast communication Remote invocation – common communication paradigm in distributed systems. Two-way exchange between communicating entities, common techniques; RPC, RMI, request-reply protocols Indirect communication– E.g. group communication, publish-subscribe systems, message queues, tuple spaces, distributed shared memory Isha Padhy, Department of CSE, CBIT, Hyderabad 6
- 7. Indirect communication • Groupcommunication • Publish- subscribe systems(Event Based systems) • Message queues • Tuple spaces • Distributed shared memory Isha Padhy, Department of CSE, CBIT, Hyderabad 7
- 8. Centralized Architecture: Client- ServerModel - Components are server, client , communication Server Client Client invocation result Server invocation result Process: Key: Computer: Isha Padhy, Department of CSE, CBIT, Hyderabad 8
- 9. Layered Architecture - Acomplex system partitioned into layers with each layer using service offered by layer below. Application , Services Middleware Operating System Computer and network hardware Platform Isha Padhy, Department of CSE, CBIT, Hyderabad 9
- 10. Example : Internetsearch engine Isha Padhy, Department of CSE, CBIT, Hyderabad 10
- 11. Tiered Architecture • Techniqueto organize functionality of a given layer and place this functionality into appropriate servers. • The functional decomposition is as - Presentation Logic - Application logic - Data Logic Isha Padhy, Department of CSE, CBIT, Hyderabad 11
- 12. 2 tier Architecture •Server provides processing and data management; client provides simple graphical display (thin-client) • At the other extreme, all application processing and some data resides at the client (fat-client approach) Isha Padhy, Department of CSE, CBIT, Hyderabad 12
- 13. 3 Tier Architecture Anexample of a server acting as client. -In some applications servers may also need to be clients, leading to a three level architecture. Ex -Distributed transaction processing -Web servers that interact with database servers Isha Padhy, Department of CSE, CBIT, Hyderabad 13