Distributed Computing: Introduction Department of Electrical & - PDF document

10/22/2009 Distributed Computing: Introduction Department of Electrical & Computer Engineering Rutgers University Definition of a Distributed System (1) A distributed system is: A collection of independent computers that appears to its users as a single coherent system. 1

10/22/2009 Definition of a Distributed System (2) 1.1 A distributed system organized as middleware. Note that the middleware layer extends over multiple machines. Distributed Systems System where hardware/software components located at networked computers communicate and coordinate their actions only by message passing…. – Concurrency – No global clock – Independent failures – … 2

10/22/2009 Distributed Computing Issues Heterogeneity – Networks, hardware, OS, programming language, data representations, etc. • Interoperability: Middleware, mobile code, protocols Openness – Access, extendibility, … Security – Confidentiality, integrity, availabilty Scalability Failure Handling – Detecting failures, masking failures, tolerating failures, tolerating failures, recovery from failures, redundancy Concurrency – Consistency, causality, mutual exclusion, etc, .. Transparency Transparency in a Distributed System ������������ ����������� �������������������������������������������������� ������ �������������������� �������� �������������������������������� ���������� ������������������������������������������������� ��������������������������������������������� ���������� ��������������������� ���������������������������������������������� ����������� ����������������� ���������������������������������������������� ����������� ����������������� ������� ������������������������������������������� ������������������������ �������������������������� ����������� ������! Different forms of transparency in a distributed system. 3

10/22/2009 Openness Openness means that a number of different platforms can be used in a network, all that is needed is some common protocol for them to communicate Scalability Problems ������� ������� ��������"����������� ����������������������������� ��������"������� �����������#������������������! ��������"������������� $������������������������������������������ Examples of scalability limitations. 4

10/22/2009 Scaling Techniques (1) 1.4 The difference between letting: a) a server or b) a client check forms as they are being filled Scaling Techniques (2) 1.5 An example of dividing the DNS name space into zones. 5

10/22/2009 Clients and Servers 1.25 General interaction between a client and a server. Processing Level 1-28 The general organization of an Internet search engine into three different layers 6

10/22/2009 Multitiered Architectures (1) 1-29 Alternative client-server organizations (a) – (e). Multitiered Architectures (2) 1-30 An example of a server acting as a client. 7

10/22/2009 Modern Architectures 1-31 An example of horizontal distribution of a Web service. 8