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Lezione 2a - 14 ottobre 2009

Il materiale didattico usato in questo corso è stato mutuato da quello utilizzato da Paolo Veronesi per il corso di Griglie Computazionali per la Laurea Specialistica in Informatica tenutonell’anno accademico 2008/09 presso l’Università degli Studi di Ferrara.

Paolo Veronesi

paolo.veronesi@cnaf.infn.it, pveronesi@unife.it


Università degli Studi di Bari – Corso di Laurea Specialistica in Informatica

“Tecnologia dei Servizi “Grid e cloud computing”

A.A. 2009/2010

Giorgio Pietro Maggigiorgio.maggi@ba.infn.it, http://www.ba.infn.it/~maggi

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Grid: the “common market”

(definitions and implementations)

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Power Grid inspiration: seamlessly delivering electricity as a utility to users

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Grid history

Name “Grid” chosen by analogy with electric power grid (Foster and Kesselman 1997)

Vision: plug-in computer for processing power just like plugging in toaster for electricity.

Concept has been around for decades (distributed computing, metacomputing)

Key difference with the Grid is to realise the vision on a global scale.

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, the present, …

  • CPU - Memory

  • Disc - Input/Output
















The Grid Revolution

The past

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virtual services

virtual services





virtual services

virtual services

The Grid Revolution

…the future: The Grid!

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Mobile Access















Supercomputer, PC-Cluster


Data-storage, Sensors, Experiments


Internet, networks

The Grid Metaphor

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The Grid Problem


flexible, secure, coordinated resource sharing among dynamic collections of individuals, institutions, and resources

From “The Anatomy of the Grid: Enabling Scalable Virtual Organizations”

enable “groups of users (virtual organizations)” to share geographically distributed resources as they pursue common goals – assuming the absence of…

central location,

central control,


existing trust relationships.

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Virtual Organizations

Virtual organization (VO): a set of individuals and/or institutions identified by the same set of rules, which define:

the resources shared (what);

the individual users allowed to share (who);

conditions under which sharing occurs (how).

VOs represent “community overlays” on classic organization structures. They can be large or small, static or dynamic.

VO membership:

Single users and users of the same institution can be members of different VOs













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Virtual Organizations (cont)


An industrial consortium

Students from different university departments using computing power for their simulation projects

physicists from different research institutions involved in a the same experiment implementation, using the Grid for analysis of the data generated by the experiment

Astronomers from various research institutes analyzing data gathered by multiple telescopes all over the world

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Authentication and authorization

Resource sharing requires owners to make resources available, subject to contraints on when, where and what can be done

This requires:

Policies and mechanisms to express them in Policy Decision Points

Authentication: the establishment of the identity of a consumer

Authorization: determining whether an operation is consistent with resource sharing rules applicable to the consumer at Policy Enforcement Points

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Some Important Definitions

Grid Computing



Network enabled service

Application Programmer Interface (API)

Software Development Kit (SDK)


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1. Grid Computing (1/4)

Early definition:

“We will probably see the spread of computer utilities, which, like present electric and telephone utilities, will service individual homes and offices across the country” (Len Kleinrock, 1969)

The Grid:

“A computational Grid is a hardware and software infrastructure that provides dependable, consistent, pervasive and inexpensive access to high-end comptational capabilities” (I.Foster, C.Kesselman: The Grid: Blueprint for a New Computing Infrastructure”, 1998)

and: “because of the focus on dynamic cross-organization sharing, Grid technologies complement rather than compete with esisting distributed computing technologies” (I.Foster et al., The Anatomy of the Grid, 2001)

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1. Grid computing: characteristics (2/4)

The three fundamental properties of Grid computing:

Large-scale coordinated management of resources belonging to different administrative domains (multi-domain vs single domain)

 Grid computing involves multiple management systems

Standard, open, multi-purpose protocols and interfaces that provide a range of services (standard vs proprietary)

Grid computing supports heterogeneous user applications

Delivery of complex Quality of Service (QoS): Grid computing allows its constituent resources to be used in a coodinated fashion to deliver various types of QoS, such as respons time, throughput, avaiability, reliability, security, etc.

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1. Grid Computing (3/4)

Examples of non-Grid systems:

Cluster management systems on a parallel computer or on a Local Area Network

Sun Grid Engine

Load Sharing Facility (LSF, by Platform)

Portable Bach System (PBS, by Veridian)

The World Wide Web:


Based on general-purpose protocols accessing distributed resources

  • Complete kwowledge of system state and user’s requests  centralized control

  • No coordinated use of independent resources (no protocols for negotiation and sharing, yet)

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Grid as a multi-institutional infrastructure


seamless collaboration

Intra-site resource

Virtual organization

local credential

Grid-level credential

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The three main capabilities of a Grid middleware

Virtualization of users and resources

  • Mapping virtual resources to physical resources

Grid system

  • Mapping virtual users to physical users


Site A

Site B

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1. Grid Computing (4/4)

The importance of standardization:

The Grid:

open, general-purpose and using standard protocols

A Grid:

no standardization and interoperability between services – current situation

Similarly: an Internet (based on proprietary protocols, as in the early ages of networking) vs the Internet (based on the IP protocol)

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2. Resource

An entity that is to be shared

E.g., computers, storage, data, software

Does not have to be a physical entity

E.g., Condor pool, distributed file system, …

Defined in terms of interfaces, not devices

E.g. scheduler such as LSF and PBS define a compute resource

Open/close/read/write define access to a distributed file system, e.g. NFS, AFS, DFS

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3. Grid Protocol

A formal description of message formats and a set of rules for message exchange, which defines one of the basic mechanisms of Grid Computing

Rules may define sequence of message exchanges

Protocol may define state-change in end-points triggered by a given sequence of exchanged messages, e.g., file system state change

Protocols, some examples:

Management of credentials and policies in case of multi-domain resources

Secure remote access

Co-allocation of multiple resources

Information query protocols

Data management protocols

Good protocols are designed to do one thing; for this reason, the Grid architecture relies on layering of protocols. i.e. through the composition of multiple, simple protocols.

Examples of protocols

IP, TCP, Transport Layer Security (was Secure Socket Layer), HTTP, Kerberos

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4. Network Enabled Services

Services are defined by:

the protocol spoken, as protocols allow interaction between different services

the behaviour implemented.


Resource access service, Resource discovery, Co-scheduling, Data replication, etc.

Services hide the complexity of resource implementations

Examples: FTP and Web servers

FTP Server

Web Server

HTTP Protocol

FTP Protocol

Telnet Protocol

Transport Layer Security Protocol

TCP Protocol

TCP Protocol

IP Protocol

IP Protocol

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5. Application Programming Interface (API)

A specification for a set of routines to facilitate application development

Refers to definition, not implementation (several implementations of the same API are possible)

APIs are a complement of protocols, as without protocols interoperability between APIs would be solved only case by case with specific implementations

Specification of an API is often language-specific

Routine name, number, order and type of arguments; mapping to language constructs

Behavior or function of routine

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6. Software Development Kit

A particular instantiation of an API

Software Development Kits consist of libraries and tools

Provides implementation of API specification

One API can have multiple SDKs

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7. Syntax

Rules for encoding information, e.g.

XML, Condor ClassAds, Globus Resource Specification Language

X.509 certificate format (RFC 2459)

Distinct from protocols

One syntax may be used by many protocols (e.g., XML) and be useful for several purposes

Syntaxes may be layered


Important to understand layerings when comparing or evaluating syntaxes

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APIs and Protocols are Both Important

Standard APIs/SDKs are important

They enable application portability

But without standard protocols, interoperability is hard (every SDK speaks every protocol?  infeasible)

Standard protocols are important

Enable cross-site interoperability

Enable shared infrastructure

But without standard APIs/SDKs, application portability is hard (different platforms access protocols in different ways)

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A Protocol can have Multiple APIs

TCP/IP APIs: BSD sockets, Winsock, …

The protocol provides interoperability: programs using different APIs can exchange information

I don’t need to know remote user’s API



WinSock API

Berkeley Sockets API

TCP/IP Protocol: Reliable byte streams

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