Software Concepts. Uniprocessor Operating Systems. System software structures. CIS 505: Software Systems Architectures of Distributed Systems

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1 CIS 505: Software Systems Architectures of Distributed Systems System DOS Software Concepts Description Tightly-coupled operating system for multiprocessors and homogeneous multicomputers Main Goal Hide and manage hardware resources NOS Loosely-coupled operating system for heterogeneous multicomputers (LAN and WAN) Offer local services to remote clients Insup Lee Department of Computer and Information Science University of Pennsylvania CIS 505, Spring 2007 Middleware Additional layer atop of NOS implementing generalpurpose services Software more important for users o Connecting users and resources o Developing software for distributed systems Provide distribution transparency 1 CIS 505, Spring 2007 Architectures 2 System software structures Uniprocessor Operating Systems DOS (Distributed Operating Systems) o Uniprocessor OS, Mutliprocessor OS, Multicomputer OS o Global IPC, file system interface o Distributed Shared Memory NOS (Network Operating Systems) o Loosely coupled-software on loosely-couple hardware o rlogin, rcp, file servers for shared file, etc Middleware Separating applications from operating system code through a microkernel. CIS 505, Spring 2007 Architectures 3 CIS 505, Spring 2007 Architectures 4 1

Information Science University of Pennsylvania CIS 505, Spring 2007 Middleware Additional layer atop of NOS implementing generalpurpose services Software more important for users o Connecting users

2 Multicomputer Operating Systems (1) Multicomputer Operating Systems (2) General structure of a multicomputer operating system Alternatives for blocking and buffering in message passing. CIS 505, Spring 2007 Architectures 5 CIS 505, Spring 2007 Architectures 6 Example Multicomputer Operating Systems (3) Sender Receiver print (before send) send ( my msg ) print (after send) print (before receive) receive (msg) print (after receive) Synchronization point Block sender until buffer not full Block sender until message sent Block sender until message received Block sender until message delivered Send buffer Yes Reliable comm. guaranteed? t necessary t necessary Necessary Necessary Relation between blocking, buffering, and reliable communications. Dealing with failures. CIS 505, Spring 2007 Architectures 7 CIS 505, Spring 2007 Architectures 8 2

(before receive) receive (msg) print (after receive) Synchronization point Block sender until buffer not full Block sender until message sent Block sender until message received Block sender until

3 Distributed Shared Memory Systems (1) Distributed Shared Memory Systems (2) a) Pages of address space distributed among four machines b) Situation after CPU 1 references page 10 c) Situation if page 10 is read only and replication is used 1.18 False sharing of a page between two independent processes. CIS 505, Spring 2007 Architectures 9 CIS 505, Spring 2007 Architectures 10 Network Operating System (1) Network Operating System (2) General structure of a network operating system. Two clients and a server in a network operating system. CIS 505, Spring 2007 Architectures 11 CIS 505, Spring 2007 Architectures 12 3

CIS 505, Spring 2007 Architectures 9 CIS 505, Spring 2007 Architectures 10 Network Operating System (1) Network Operating System (2) 1-19 1-20 General

4 Web-sever Architectures Middleware for Distributed Systems 1-31 Middleware is a layer of software between applications and OS that gives a uniform interface Central to developing distributed applications Different types o Document based (world-wide web) o File-system based (e.g., NFS) o Shared object-based (CORBA) o Coordination based (Linda, Publish-subscribe, Jini) An example of horizontal distribution of a Web service. CIS 505, Spring 2007 Architectures 13 CIS 505, Spring 2007 Architectures 14 Coordination-based Approach Middleware Layer applications middleware applications middleware OS network OS network Linda: the tuple space o In ( fred, 1958), Read ( fred, x), Out( fred, 1958) In an open middleware-based distributed system, the protocols used by each middleware layer should be the same, as well as the interfaces they offer to applications CIS 505, Spring 2007 Architectures 15 CIS 505, Spring 2007 Architectures 16 4

5 Comparison between Systems System Architectures for Applications Item Degree of transparency Same OS on all nodes Number of copies of OS Basis for communication Resource management Scalability Openness Distributed OS Multiproc. Very High Yes 1 Shared memory Global, central Closed Multicomp. High Yes N Messages Global, distributed Moderately Closed Network OS Low N Files Per node Yes Open Middlewarebased OS High N Model specific Per node Varies Open Centralized Architecture o Client-server model o Application layering o Multitiered architecture Decentralized Architecture o Peer-to-peer architecture Distributed hash table (DHT) o Overlay Networks Hybrid Architectures CIS 505, Spring 2007 Architectures 17 CIS 505, Spring 2007 Architectures 18 The Client and Server Model An Example Client and Server (1) 1.25 General interaction between a client and a server. Protocols (e.g., HTTP, SMTP, MIME, etc.) The header.h file used by the client and server. CIS 505, Spring 2007 Architectures 19 CIS 505, Spring 2007 Architectures 20 5

High Yes N Messages Global, distributed Moderately Closed Network OS Low N Files Per node Yes Open Middlewarebased OS High N Model specific Per node Varies Open Centralized Architecture o

6 An Example Client and Server (2) An Example Client and Server (3) 1-27 b A sample server. CIS 505, Spring 2007 Architectures 21 A client using the server to copy a file. CIS 505, Spring 2007 Architectures 22 Application Layering Figure 2-4. The simplified organization of an Internet search engine into three different layers. Multitiered Architectures (1) The simplest organization is to have only two types of machines: A client machine containing only the programs implementing (part of) the user-interface level A server machine containing the rest, o the programs implementing the processing and data level CIS 505, Spring 2007 Architectures 23 CIS 505, Spring 2007 Architectures 24 6

Multitiered Architectures (1) The simplest organization is to have only two types of machines: A client machine containing only the programs implementing (part of) the

7 Multitiered Architectures (2) Multitiered Architectures (3) Figure 2-5. Alternative client-server organizations (a) (e). Figure 2-6. An example of a server acting as client. CIS 505, Spring 2007 Architectures 25 CIS 505, Spring 2007 Architectures 26 Structured Peer-to-Peer Architectures (1) DHT (Distributed Hash Table) Ex: the mapping of data items onto nodes in Chord. Structured Peer-to-Peer Architectures (2) Content Addressable Network (CAN) Figure 2-8. (a) The mapping of data items onto nodes in CAN. CIS 505, Spring 2007 Architectures 27 CIS 505, Spring 2007 Architectures 28 7

CIS 505, Spring 2007 Architectures 25 CIS 505, Spring 2007 Architectures 26 Structured Peer-to-Peer Architectures (1) DHT (Distributed Hash Table)

8 Structured Peer-to-Peer Architectures (3) Topology Management of Overlay Networks Figure 2-8. (b) Splitting a region when a node joins. CIS 505, Spring 2007 Architectures 29 Structured overlay based on ranking functions o E.g., Semantic proximity CIS 505, Spring 2007 Architectures 30 Topology Management of Overlay Networks Superpeers Figure Generating a specific overlay network using a twolayered unstructured peer-to-peer system [adapted with permission from Jelasity and Babaoglu (2005)]. CIS 505, Spring 2007 Architectures 31 Figure A hierarchical organization of nodes into a superpeer network. CIS 505, Spring 2007 Architectures 32 8

Generating a specific overlay network using a twolayered unstructured peer-to-peer system [adapted with permission from Jelasity and Babaoglu (2005)].

9 Self-Management of Distributed Systems The Feedback Control Model Issues o What to monitor o How to monitor o How to evaluate o How to adapt o Three steps o Monitor o Check o Steer/Adapt Figure The logical organization of a feedback control system. CIS 505, Spring 2007 Architectures 33 CIS 505, Spring 2007 Architectures 34 Possible techniques for adaption 1. Changing system parameter values 2. Micro resets 3. Dynamic replacement of components 4. System regeneration by global reset and restriction to essential functionality Example: Systems Monitoring with Astrolabe Figure Data collection and information aggregation in Astrolabe. CIS 505, Spring 2007 Architectures 35 CIS 505, Spring 2007 Architectures 36 9

CIS 505, Spring 2007 Architectures 33 CIS 505, Spring 2007 Architectures 34 Possible techniques for adaption 1. Changing system parameter values 2. Micro resets 3.

10 Example: Differentiating Replication Strategies in Globule (1) Example: Differentiating Replication Strategies in Globule (2) Figure The edge-server model assumed by Globule. Figure The dependency between prediction accuracy and trace length. CIS 505, Spring 2007 Architectures 37 CIS 505, Spring 2007 Architectures 38 Example: Automatic Component Repair Management in Jade Steps required in a repair procedure: Terminate every binding between a component on a nonfaulty node, and a component on the node that just failed. Request the node manager to start and add a new node to the domain. Configure the new node with exactly the same components as those on the crashed node. Re-establish all the bindings that were previously terminated. CIS 505, Spring 2007 Architectures 39 10

CIS 505, Spring 2007 Architectures 37 CIS 505, Spring 2007 Architectures 38 Example: Automatic Component Repair Management in Jade Steps required in a repair procedure: Terminate every binding

2.1 What are distributed systems? What are systems? Different kind of systems How to distribute systems? 2.2 Communication concepts

Chapter 2 Introduction to Distributed systems 1 Chapter 2 2.1 What are distributed systems? What are systems? Different kind of systems How to distribute systems? 2.2 Communication concepts Client-Server