1 CS 6823 ASU Chapter 2 Architecture

2 CS 6823 ASU Overview Architecture overview Architectural styles Software architectures Architectures versus middleware Self-management in distributed systems

3 CS 6823 ASU Uniprocessor Operating Systems Multitasking –A virtual machine to application CPU –Kernel mode and user mode System call –Programming interfaces between application and kernel Monolithic Kernel & Microkernel

4 CS 6823 ASU Multiple CPU System Shared/Private Memory –Multiprocessors & Multicomputers Interconnection network –Bus & Switched

5 CS 6823 ASU Homogeneous Multicomputer Systems System Area Network(SAN) –Bus-based multicomputer 100M,Fast Ethernet, Broadcast 25~100 nodes –Switch-base multicomputer Meshes Hypercubes MPP COW (Clusters)

6 CS 6823 ASU Shared-Memory Architectures Examples: Cray C90, SGI Power Challenge

7 CS 6823 ASU Distributed (Multi-Private) Memory Architectures Examples: –NUMA: Cray T3E, SGI Origin 2000 (connected on memory bus) –UMA: Sun Enterprise (connected on memory bus) –Clusters: IBM SP-2, UC Berkeley NOW (connected on I/O bus)

8 CS 6823 ASU Cluster Architectures

9 CS 6823 ASU Network Operating System A collection of OSs of computers connected through a network incorporating modules to provide access to remote resources –Users are aware of file locations; remotely log-in

10 CS 6823 ASU Network Operating System Two clients and a server in a network operating system. 1-20

11 CS 6823 ASU Distributed Operating Systems Requirements –Provide users with a single coherent computer system –Hide distribution of resources –Mechanisms for resource protection –Secure communication Definition of Distributed OS –To users, it looks like ordinary centralized OS, but runs on multiple and independent CPUs use of multiple processors is invisible user views system as a virtual uniprocessor

12 CS 6823 ASU Adapted from Instructor’s Guide for Distributed Systems: Concepts and Design Edn. 4 and Slides of UCCS © Pearson Education 2005 Distributed Operating Systems Single System Image: sharing local and remote resources in the same way Homogeneous and inextensible

13 CS 6823 ASU Structure of Distributed Operating Systems User Space Kernel UPSVR User Space Kernel SVR

14 CS 6823 ASU Distributed vs. Network Operating Systems Transparency –How aware are users of the fact that multiple computers are being used? Network OS –Users are aware where resources are located –Network OS is built on top of centralized OS –Handles interfacing and coordination between local OSs Distributed OS –Designed to control and optimize operations and resources in distributed systems, but giving a virtual single system to users

15 CS 6823 ASU Distributed Systems: Positioning Middleware General structure of a distributed system as middleware

16 CS 6823 ASU Software Concepts An overview between DOS (Distributed Operating Systems) NOS (Network Operating Systems) Middleware SystemDescriptionMain Goal DOS Tightly-coupled operating system for multi-processors and homogeneous multicomputers Hide and manage hardware resources NOS Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) Offer local services to remote clients Middleware Additional layer atop of NOS implementing general-purpose services Provide distribution transparency

17 CS 6823 ASU Comparison between Systems A comparison between multiprocessor operating systems, multicomputer operating systems, network operating systems, and middleware based distributed systems. Item Distributed OS Network OS Middleware- based DS Multiproc.Multicomp. Degree of transparency Very HighHighLowHigh Same OS on all nodesYes No Number of copies of OS 1NNN Basis for communication Shared memory MessagesFilesModel specific Resource management Global, central Global, distributed Per node ScalabilityNoModeratelyYesVaries OpennessClosed Open

18 CS 6823 ASU Distributed Shared Memory Build a “virtual” memory address over distributed multiple physical memories; an abstraction for data sharing between computers that do not share physical memory –load/store vs. send/receive message passing –Run-time system support for transparent accesses

19 CS 6823 ASU Organization of Distributed Systems Software architectures –How to organize software components –How they should interact System architectures –Final instantiation of software architectures on real machines Autonomic systems –A distributed system monitor its own behavior and taking appropriate measures when needed

20 CS 6823 ASU Software Architectures Goal: Distribution transparency –Trade-offs between performance, fault tolerance, ease-of- programming, and so on Component: –Modular units with well-defined required and provided interfaces Connector –Mechanism to mediate communication coordination, or cooperation among components

21 CS 6823 ASU Architectural Styles Important styles of architecture for distributed systems –Layered architectures –Object-based architectures –Data-centered architectures –Event-based architectures

22 CS 6823 ASU Layered Architectural Style A component at layer L i is allowed to call components at the underlying layer L i-1

23 CS 6823 ASU Object-based Architectural Style Each object corresponds to what we have defined as a component These components are connected through a (remote) procedure call mechanism

24 CS 6823 ASU Data-centered Architectural Style Components communicate through a common (passive or active) repository –Network applications: communicate through shared distributed file systems –Web applications: processes communicate through the use of shared Web-based data services

25 CS 6823 ASU Event-based Architectural Style Processes essentially communicate through the propagation of events –Optionally also carry data Publish/subscribe systems –Only subscribed processes will receive the published events –Referentially decoupled: Processes are loosely coupled

26 CS 6823 ASU Shared Data-space Architectural Style Combine event-based architectures and data- centered architectures –Processes are decoupled in time

27 CS 6823 ASU System Architectures Centralized Architectures Decentralized Architectures Hybrid Architectures

28 CS 6823 ASU Centralized Architectures Client-server model: –Processes are divided into two (possibly overlapping) groups –Server: a process implementing a specific service –Client: a process sending a request to a server and subsequently waiting for the server's reply

29 CS 6823 ASU Communication between Clients and Servers Connectionless protocol –Efficient, but unreliable Good for LANs –Idempotent: an operation can be repeated multiple times without harm Connection-oriented protocol –Inefficient, but reliable Good for WANs

30 CS 6823 ASU Application Layering Traditional three-layered view: –User-interface layer Contains units for an application’s user interface –Processing layer Contains the functions of an application, i.e. without specific data –Data layer Contains the data that a client wants to manipulate through the application components Observation: –This layering is found in many distributed information systems, using traditional database technology and accompanying applications.

31 CS 6823 ASU Internet Search Engine The core : information retrieval part

32 CS 6823 ASU More Examples A Stock Brokerage System –User Interface –Process Level Analysis of financial data requires sophisticated methods and techniques from statistics and artificial intelligence –Data Level Financial database Word Processor

33 CS 6823 ASU Data Level Persistency of data Keeping data consistent across different applications Database –Relational database –Object-oriented database