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Centralized vs. Decentralized Design for Internet Applications. I. Adriana Iamnitchi Department of Computer Science The University of Chicago. Internet Applications. Components that build the Internet itself (DNS …)

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centralized vs decentralized design for internet applications

Centralized vs. Decentralized Design for Internet Applications

I

Adriana Iamnitchi

Department of Computer Science

The University of Chicago

internet applications
Internet Applications
  • Components that build the Internet itself (DNS …)
  • Tools that connect the user to Internet resources (browsers, applets, CGIs, ...)
  • Services that can be accessed through Internet (e-commerce, e-banking, newspapers, e-libraries, …)
  • Applications that run on a collection of Internet-connected resources ([email protected], …)
  • Tools that create new environments over the Internet (middleware services)

TWIST 2000

internet connected resources
Internet-Connected Resources
  • Unreliable communication
  • Unreliable resources
  • Highly heterogeneous environment
  • Potentially very large number of resources
  • Potentially highly variable number of resources

TWIST 2000

centralized or decentralized
Centralized or Decentralized?
  • Applications
  • Middleware services

TWIST 2000

internet connected resources1
Internet-Connected Resources
  • Unreliable communication
  • Unreliable resources
    • Fault-tolerance mechanisms
  • Highly heterogeneous environment
    • Asynchronous algorithms
  • Potentially very large number of resources
  • Potentially highly variable number of resources
    • Scalability

TWIST 2000

application design decentralized
Application Design: Decentralized!

What about:

  • Distributed management control?
  • Fault tolerance in distributed, asynchronous systems?
  • Termination detection?
  • Communication costs?
  • Security?

TWIST 2000

experience with metaneos
Experience with MetaNEOS
  • Solving very large optimization problems on metacomputing platforms
  • Branch-and-bound search algorithms:
    • Search for optimal solution
    • Successive decomposition of the original problem
    • Elimination of unpromising subproblems based on the best known solution

TWIST 2000

fully decentralized b b solution
Fully decentralized B&B: Solution
  • Process management: group membership based on epidemic communication
  • Fault-tolerance: tree-based encoding of the problem space.
    • Report completed problems
    • Unsolved problems detected/restored based on completed problems
    • Price: redundant work
  • Termination detection: tree contraction
  • Dynamic load balancing

TWIST 2000

experience with metaneos1
Experience with MetaNEOS
  • Decentralized design is wonderful
  • Meantime, the centralized implementation produces results, because:
    • Centralized code already exists (master-worker)
    • Available resources: hundreds resources working simultaneously (Condor testbed)
    • Centralized code still efficient on relatively small collections of resources

TWIST 2000

centralized or decentralized1
Centralized or Decentralized?
  • Applications
  • Middleware services

TWIST 2000

middleware services for computational grids
Middleware Services for Computational Grids
  • Computational Grids: hardware and software infrastructure that provides access to computational capabilities.
  • Middleware services: responsible for application performance
    • Information Services
    • Service Location Services (Resource Discovery)
    • Resource Management
    • Security
    • Fault tolerance/detection

TWIST 2000

information service resource discovery
Information Service & Resource Discovery
  • Information Service
    • Resources (networks, computers, applications, …)
    • Users
  • Resource Discovery: “Give me n resources with attribute X”
    • Input: set of resource attributes
    • Output: set of resources
    • Attributes: hardware characteristics, current load, network connection, existent/available software, data, etc.

TWIST 2000

resource discovery requirements
Resource Discovery: Requirements
  • Scalable
    • Increasing number of resources
    • Increasing number of users
  • Reliable
  • Flexible (heterogeneity support)
    • Heterogeneity:
      • Administrative level (policies)
      • Technical level (hardware and software)
    • Support for changing environment

TWIST 2000

resource discovery requirements1
Resource Discovery: Requirements
  • Efficient
  • Accurate
  • Secure
  • No global hierarchy
    • Politically difficult for wide area (impossible?)
    • Hierarchical structures are resistant to change

TWIST 2000

globus
Globus
  • Toolkit that builds computational grids
  • Components:
    • Metacomputing Directory Service
    • Heartbeat Monitor
    • Grid Security Infrastructure
    • Globus Resource Allocation Manager
    • Global Access to Secondary Storage
    • Nexus

TWIST 2000

globus mds step 1
Globus’ MDS – Step 1

C=US, o=Globus,

o=UC, ou=CS

C=US, o=Globus,

o=ANL, ou=MCS

C=US, o=Globus,

o=USC, ou=ISI

TWIST 2000

globus mds step 2
Globus’ MDS: Step 2

C=US, o=Globus,

o=ANL, ou=MCS

C=US, o=Globus,

o=UC, ou=CS

C=US, o=Globus,

o=USC, ou=ISI

TWIST 2000

globus mds step 3
Index

Server A2

Index

Server A1

Globus’ MDS: Step 3

o=Grid, dc=mcs, dc=anl, dc=gov

Organizational

Server

Organizational

Server

o=Grid, dc=isi, dc=edu

o=Grid, dc=cs, dc=uchicago, dc=edu

Organizational

Server

TWIST 2000

decentralized information service
Decentralized Information Service
  • More difficult than the centralized design:
    • Resource discovery based on attributes:
      • Rich set of queries to support
      • Compound queries
      • Static and dynamic data
      • Access policies
  • Necessary

TWIST 2000

conclusions
Conclusions
  • Applications running on collections of Internet-connected resources: may be centralized or decentralized.
  • Middleware services must be decentralized.

TWIST 2000

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