Tiziana FerrariAn Introduction to Grid Computing1 [email protected] INFN – CNAF Corso...

Tiziana Ferrari An Introduction to Grid Computing 1

An Introduction to Grid Computing

[email protected] – CNAF

Corso di Laurea specialistica in InformaticaAnno Acc. 2005/2006

Sources: 1 .Introduction to Grid Computing, Globus Project, Argonne National Laboratory, http://www.globug.org/2. The Anatomy and Physiology of the Grid, B.Ramamurthy, 10/4/2004


Outline

• PART I: Introduction to Grid Computing

• PART II: Some Definitions

• PART III: Grid Architecture


PART IIntroduction


The Grid Problem

• Purpose: – 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,

• omniscience,

• existing trust relationships.


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

u1

u2

u3

u5

u9

VO3VO2VO1

u8

u4

u7

u6


Virtual Organizations (cont)

• Examples:– 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


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


Elements of the Problem

• Resource sharing: sharing issues today are not adequately addressed by existing technologies.– Complex requirements: “run program X at site Y subject to

community policy P, providing access to data at Z according to policy Q”

– High performance: unique demands of advanced & high-performance systems

– Heterogeneous resources: computers, storage, sensors, networks, …

– Sharing always conditional: issues of trust, policy, negotiation, payment, …

• Coordinated problem solving– It extends the simple client-server: distributed data analysis and

computation

Tiziana Ferrari An Introduction to Grid Computing 9Image courtesy Harvey Newman, Caltech

Example: usage of Data Grids in High Energy Physics

Tier2 Centre ~1 TIPS

Online System

Offline Processor Farm

~20 TIPS

CERN Computer Centre

FermiLab ~4 TIPSFrance Regional Centre

Italy Regional Centre

Germany Regional Centre

InstituteInstituteInstituteInstitute ~0.25TIPS

Physicist workstations

~100 MBytes/sec

~100 MBytes/sec

~622 Mbits/sec

~1 MBytes/sec

There is a “bunch crossing” every 25 nsecs.

There are 100 “triggers” per second

Each triggered event is ~1 MByte in size

Physicists work on analysis “channels”.

Each institute will have ~10 physicists working on one or more channels; data for these channels should be cached by the institute server

Physics data cache

~PBytes/sec

~622 Mbits/sec or Air Freight (deprecated)




Caltech ~1 TIPS

~622 Mbits/sec

Tier 0Tier 0

Tier 1Tier 1

Tier 2Tier 2

Tier 4Tier 4

1 TIPS is approximately 25,000

SpecInt95 equivalents


Why now? The network

• The Internet: universal connectivity

• Network vs. computer performance– Computer speed doubles every

18 months

– Network speed doubles every 9 months

– Difference = order of magnitude per 5 years

Moore’s Law vs. storage improvements vs. optical improvements. Graph from Scientific American (Jan-2001) by Cleo Vilett, source Vined Khoslan, Kleiner, Caufield and Perkins.


GEANT2: the European research backbone – topology (Oct 2005)

Dark fiber

10 Gb/s

2.5 Gb/s


PART IISome Definitions


Some Important Definitions

1. Grid Computing

2. Resource

3. Protocol

4. Network enabled service

5. Application Programmer Interface (API)

6. Software Development Kit (SDK)

7. Syntax


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)


1. Grid computing: characteristics (2/4)

• The three fundamental properties of Grid computing:

1. Large-scale coordinated management of resources belonging to different administrative domains (multi-domain vs single domain) Grid computing involves multiple management systems

2. Standard, open, multi-purpose protocols and interfaces that provide a range of services (standard vs proprietary) Grid computing supports heterogeneous user applications

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



• 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)

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

– The World Wide Web:• Open

• Based on general-purpose protocols accessing distributed resources

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



• 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)


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


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


4. Network Enabled Services• Services are defined by:

– the protocol spoken, as protocols allow interaction between different services

– the behaviour implemented.

• Examples:– Resource access service, Resource discovery, Co-scheduling, Data

replication, etc.

• Services hide the complexity of resource implementations

• Examples: FTP and Web servers

Web Server

IP Protocol

TCP Protocol

Transport Layer Security Protocol

HTTP Protocol

FTP Server

IP Protocol

TCP Protocol

FTP Protocol

Telnet Protocol


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 could 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


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


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– E.g., HTML XML ASCII

– Important to understand layerings when comparing or evaluating syntaxes


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)


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

TCP/IP Protocol: Reliable byte streams

WinSock API Berkeley Sockets API

Application Application


PART IIIGrid Architecture


Grid Architecture: Definition (1/2)

• The Grid Architecture:

– identifies the fundamental system components (services and VOs);

– specifies purpose and function of these components;

– indicates how these components interact with each other.

– Functions:

• It identifies key areas in which services are required;

• It defines standard protocols and APIs to facilitate creation of interoperable Grid systems and portable applications.

• Grid architecture protocols define the basic communication mechanisms by which:– Virtual Organization users and resources negotiate, establish, manage and exploit

sharing relationships;

– different services interact.

• Grid architecture services are the components whose standardization facilitates extensibility, interoperability, portability and code sharing.


Grid Archticture: Definition (2/2)

S1

S2

S4

S3

U3U4

U5

U8U7

U6

U1

U2

VO1

VO2COMPONENTS

1. VOs and their users2. Services3. Protocols: - between services - between services and VOs

protocol

protocolprotocol

protocol

protocolprotocol


Resource Sharing

• Address security and policy concerns of resource owners and users

• Are flexible enough to deal with many resource types and sharing modalities

• Scale: – to large number of resources, many participants, many program

components

– to large data management tasks and computing tasks


Service Sharing

1) Need for interoperability when different groups want to share resources– Diverse components, policies, mechanisms– E.g., standard notions of identity, means of communication,

resource descriptions

2) Need for shared infrastructure services to avoid repeated development, installation– E.g., one port/service/protocol for remote access to computing, not

one per tool and/or application– E.g., use of shared Certificate Authorities as they are expensive to

run

A common need for protocols & services


Layered Grid Architecture(by Analogy to the Internet Architecture)

Application

Fabric“Controlling elements locally”: Access to, & control of, resources

Connectivity“Talking to Grid elements”: communication (Internet protocols) & security

Resource“Sharing single resources”: negotiating access, controlling use

Collective“Coordinating multiple resources”: ubiquitous infrastructure services, app-specific distributed services

InternetTransport

Application

Link

Inte

rnet P

roto

col

Arch

itectu

re

Grid Architecture

Internet Architecture


Layered Grid Architecture

• Layers are ment to group services of similar nature in the same class

• They do not intend to prescribe how services at different layers interact. Communication between services at the same and/or different layer is possible, depending on the scenario.– Example 1: The workload management service (Collective layer) uses

the Resoure discovery service (still Collective layer) to find resources that match the user’s rquirements

– Example 2: an application may submit a job:• By invoking the Workload manager service (re-submission, logging and

bookkeping, input/output management, Collective)

• By invoking the resource layer through a standardized API (Resource)

• By submitting directly to a specific local resource instance (Fabric)


Protocols, Services,and APIs Occur at Each Level

Languages/Frameworks

Fabric Layer

Applications

Local Access APIs and Protocols

Collective Service APIs and SDKs

Collective ServicesCollective Service Protocols

Resource APIs and SDKs

Resource ServicesResource Service Protocols

Connectivity APIs

Connectivity Protocols


Fabric Layer (1/2)

• Examples:– Computing farm– Mass storage device – file catalogs– network link– file systems– sensors, etc.

• It provides access to the resources to which shared access is mediated by Grid protocols.

• Fabric components implement local, resource-specific operations (through internal protocols), which are transparent to the upper layers thanks to connectivity and resource level protocols, that define interfaces, not the physical internal characteristics.

• Operations at the fabric layer are triggered by resource sharing operations at a higher level


Fabric Layer: Capabilities (2/2)

• Examples of capabilities– Computational resource:

• Start programs

• Monitor execution and corresponding processes

• Management of resources (e.g. advance reservation)

• Enquiry of hw/sw capabilities, current load, queue waiting time, etc.

– Storage resource:• Put/get files

• Third party and high-performance data transfer

• Read/write subset of file

• Management of disk space, disk bandwidth, network bandwidth, CPU, etc.

• Enquiry of hw/sw characteristics, available space, bandwidth utilziation, etc.


Connectivity Layer: Protocols & Services• It supports secure communication between Fabric-layer resources by defining the core

communication and authentication protocols required for grid-specific network functions.

• Communication:– transport (e.g. IP), naming (e.g. DNS), routing, etc. (the TCP/IP protocol stack)

• Security: the Grid Security Infrastructure (GSI)– Uniform authentication, authorization, and message protection mechanisms in

multi-institutional setting– Single sign-on: users must be able to authenticate just once and then have access

to multiple resources, without further user intervention;– Delegation: a user’s program can access the resources on which the program

owner is authorized.– Integration with local security solutions: Grid security needs to interoperate

with local security solutions adopted by the resource managers– User-based trust relationship: a user can access to resources in different

domains without requiring security administrators in each domain to interact with others in different domains. In other words, authorization is only based on the user’s certificate, not on the authentication/authorization performed by other servers in different domains.

– Public key cryptography: Secure Socket Layer (SSL)– Supporting infrastructure: Certificate Authorities, certificate & key management


Resources Layer: Protocols & Services• Resource layer defines protocols, APIs, and SDKs for:

– secure negotiations,

– initiation,

– monitoring control,

– accounting,

– and payment of sharing operations on individual resources.

• Resource layer implementation relies on the Fabric layer functions.

• Two main components define this layer:– information protocols: used to obtain the information about the structure and state of the resource, e.g.:

configuration, current load and usage policy.

– management protocols: used to negotiate access to the shared resource, specifying for example QoS, advanced reservation, etc.

• Examples: – Access to compute cluster, storage, network information

– Invocation of resource service providers

– Access to local scheduler


Collective Layer: Protocols & Services• The Collective Layer contains protocols and services that coordinate multiple

resources concurrently, i.e. they capture interactions among a collection of resources.• It supports a variety of sharing behaviors without placing new requirements on the

resources being shared. Examples: – Directory services: they allow VO participants to discover the existence and/or

properties of VO resources. – Co-allocation, scheduling: they allow VO participants to request the allocation of

one or more resource for a specific purpose and the scheduling of tasks on the appropriate resources.

– Monitoring: support the monitoring of VO resources (intrusion, failure, load, ..)– Data replication: supports the management of VO storage resources to maximize

data access performance with respect to metrics such as response time, reliability, etc.

– Workload management: description, use and management of complex workflows (e.g. submission of jobs with mutual dependencies)

– Authorization servers, accounting, collaboratory services (synchronous/asynchronous exchange of messages)


Application Layer• It includes user applications that operate within a Virtual

Organization environment.• Applications are constructed such that invocation of services

and use of protocols defined at any layer are possible. For example, a given user can submit jobs by invoking services at different layers:– Collective Layer: by submitting to a Workload Manager (it can

provide: internal queue in: case of submission failure, periodic re-submission, access to logging and bookkeeping information, input/output file management)

– Resource Layer: by submitting directly to a compute resource scheduler (e.g. a local cluster)

– Connectivity Layer: by submitting to a remote cluster – Fabric Layer: by submitting to a local cluster


Open Grid Services Architecture (OGSA)

• OGSA defines the semantics of the Grid Service instances: how they are created, how lifetime is determined, how they communicate, etc.; where:– the service is a network-enabled entity providing a set of capabilities.– compositions of services are possible to form “virtual resources”

• OGSA builds on concepts and technologies from the Grid and Web services communities.

• Web services technology: it is used to define and publish (in a uniform manner) the service semantics. It defines:– defines standard mechanisms for creating, naming, and discovering

transient grid service instance; – provides location transparency and multiple protocol bindings;– supports integration with underlying native platform facilities;– lifetime management, change management, and notification,

authentication, authorization, and delegation.


ComputeResource

SDK

API

AccessProtocol

CheckpointRepository

SDK

API

C-pointProtocol

Example 1:High-Throughput Computing System

High Throughput Computing System

Dynamic checkpoint, job management, failover, staging

Brokering, certificate authorities

Access to data, access to computers, access to network performance data

Communication, service discovery (DNS), authentication, authorization, delegation

Storage systems, schedulers

Collective(App)

App

Collective(Generic)

Resource

Connect

Fabric


Example 2:Data Grid Architecture

Data Grid Application (access to distributed data)

Coherency control, replica selection, task management, virtual data catalog, virtual data code catalog, …

Replica catalog, replica management, co-allocation, certificate authorities, metadata catalogs,

Access to data, access to computers, access to network performance data, …

Communication, service discovery (DNS), authentication, authorization, delegation

Storage systems, clusters, networks, network caches, …

Collective(App)

App

Collective(Generic)

Resource

Connect

Fabric


PART IVAn example: the Globus Toolkit™


Globus Toolkit™

• A software toolkit addressing key technical problems in the development of Grid enabled tools, services, and applications– Offer a modular “set of technologies”

– Enable incremental development of grid-enabled tools and applications

– Implement standard Grid protocols and APIs

– Make available under open source license


General Approach

• Define Grid protocols & APIs– Protocol-mediated access to remote resources

– Integrate and extend existing standards

– “On the Grid” = speak “Intergrid” protocols

• Develop a reference implementation– Open source Globus Toolkit

– Client and server SDKs, services, tools, etc.

• Grid-enable wide variety of tools– Globus Toolkit, FTP, SSH, Condor, SRB, MPI, …

• Learn through deployment and applications


Fundamental Protocols

• Connectivity Layer protocols– Security: Grid Security Infrastructure (GSI)

• Resource layer:– Resource Management: Grid Resource Allocation Management

(GRAM)

– Information Services: Grid Resource Information Protocol (GRIP)

– Data Transfer: Grid File Transfer Protocol (GridFTP)

• Collective layer protocols– Information Services,

– File Replica Management,

– etc.


Collective Layer:Grid Security Infrastructure (GSI)

• Globus Toolkit implements GSI protocols and APIs, to address Grid security needs

• GSI protocols extends standard public key protocols– Standards: X.509 & Secure Socket Layer (SSL)/Transport Layer

Security (TLS)

– Extensions: X.509 Proxy Certificates & Delegation

• GSI extends standard Generic Security Service-API


Site A(Kerberos)

Site B (Unix)

Site C(Kerberos)

Computer

User

Single sign-on via “grid-id”& generation of proxy cred.

Or: retrieval of proxy cred.from online repository

User ProxyProxy

credential

Computer

Storagesystem

Communication*

GSI-enabledFTP server

AuthorizeMap to local idAccess file

Remote fileaccess request*

GSI-enabledGRAM server

GSI-enabledGRAM server

Remote processcreation requests*

* With mutual authentication

Process

Kerberosticket

Restrictedproxy

Process

Restrictedproxy

Local id Local id

AuthorizeMap to local idCreate processGenerate credentials

Ditto

GSI in Action“Create Processes at A and B

that Communicate & Access Files at C”


Resource Layer: Resource Management

• The Grid Resource Allocation Management (GRAM) protocol and client API allows programs to be started and managed on remote resources, despite local heterogeneity

• Resource Specification Language (RSL) is used to communicate requirements

• A layered architecture allows application-specific resource brokers and co-allocators to be defined in terms of GRAM services– Integrated with Condor, PBS, MPICH-G2, …


GRAM GRAM GRAM

LSF Condor NQE

Application

RSL

Simple ground RSL

Information Service

Localresourcemanagers

RSLspecialization

Broker

Ground RSL

Co-allocator

Queries& Info

Resource Management Architecture


Resource Layer: Data Access & Transfer

• GridFTP: extended version of popular FTP protocol for Grid data access and transfer

• Secure, efficient, reliable, flexible, extensible, parallel, concurrent, e.g.:– Third-party data transfers, partial file transfers

– Parallelism, striping (e.g., on PVFS)

– Reliable, recoverable data transfers

• Reference implementations– Existing clients and servers: wuftpd, ncftp

– Flexible, extensible libraries in Globus Toolkit


Collective Layer: the Grid Information Service

Large numbers of distributed “sensors” with different properties Need for different “views” of this information, depending on community

membership, security constraints, intended purpose, sensor type


The Globus Toolkit Solution (MDS-2)

Registration & enquiry protocols, information models, query languages– Provides standard interfaces to sensors

– Supports different “directory” structures supporting various discovery/access strategies


References

1. What is the Grid? A Three Point Checklist; Ian Foster, GridToday, Jul 2002.

2. The Anatomy of the Grid: Enabling Scalable Virtual Organizations, I. Foster, Carl Kesselman, S.Tuecke

3. The Physiology of the Grid, An Open Services Archtiecture for Distributed Systems Integration; I. Foster, C.Kesselman, J.M.Nick, S.Tuecke; Jun 2002.

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