Distributed Systems basics

What is Distributed System?  A Distributed System is a Collection of independent computers that appears to its users as a single coherent system.  Physical Distribution  Doesn’t Matter  Logical Distribution:  Multiple Processes  Interprocess Communication  Disjoint Address Spaces  Collective Goal

Issues  Transparency:  Access – Hide differences in representation & how a resource is accessed.  Location – Hide where a resource is located  Relocation – Hide that a resource may be moved to another location while in use.  Replication – Hide that a resource is replicated.  Concurrency – Hide that a resource may be shared.  Failure – Hide the failure & recovery of a resource.  Persistence – Hide whether a resource is in Memory or Disk  Scalability:  Horizontal  Vertical  Openness:  Standards

Issues (Cont.)  Security : o Confidentiality:  Communication bet n two parties not known to a third party. o Integrity:  Ensuring that the messages received are genuine. o Availability:  Ensuring the availability of data whenever required. o Authenticity:  Validating that the party participating in a transaction is who the party claims to be. o Non-repudiation:  Ensuring that a party can’t deny after committing an action.

Distributed Operating System (DOS)  Transparency – High  Scalability – Low  Openness – Closed  Resource Management – Global  Heterogeneity – No  Communication – Message Passing Kernel Distributed Operating System Services Distributed Application

Network Operating System (NOS)  Transparency – Low  Scalability – High  Openness – Open  Resource Management – Per Node  Heterogeneity – Yes  Communication – File Based Kernel Distributed Application NOS Services

Distributed System  Transparency – High  Scalability – Medium  Openness – Open  Resource Management – Per Node  Heterogeneity – Yes  Communication – Implementation Specific Kernel Distributed Application NOS Services Middleware Services

Examples  World Wide Web (WWW)  Sensor Network  Peer-2-Peer Network  Grid Computing  Cloud Computing

Web Services UDDI Server Client WSDL Request Client Code Generate SOAP Server Code Codewww.smartphonetech.org

Grid Computing  What is a Grid:  Coordinates resources that are not subject to centralized control.  Uses standard, open, general purpose protocols & interfaces.  Delivers non-trivial Quality of Services (QoS)  Resources are organized with heterogeneous distributed dynamic Virtual Organizations (VO)  O -> the set concrete organizations ({o})  RS -> the set or resources & services offered by a VO  I -> the interfaces for accessing RS  PY -> the set of policies ({py}) for the operation of the VO &  PL -> the set of protocols ({pl}) for the implementation of PY VO = (O, RS, I, PY, PL)

GT4, OGSA & WSRF GT4OGSAWSRF Statefull Web Services Web Services Grid Application extends requires specifies implements implemented on top ofmeet requirements of

Globus Toolkit (GT4) Machine A GateKeeper GRIS GIIS Machine B GSI MDS GRAM GridFTP GASS Cache Registrar Find Setup Job Request Job Response Job Execution

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