Centralized vs. Decentralized Design for Internet Applications Adriana Iamnitchi Department of Computer Science The University of Chicago I

6/28/2015 TWIST 2000 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 …) Tools that create new environments over the Internet (middleware services)

6/28/2015 TWIST 2000 Internet-Connected Resources Unreliable communication Unreliable resources Highly heterogeneous environment Potentially very large number of resources Potentially highly variable number of resources

6/28/2015 TWIST 2000 Centralized or Decentralized? 1. Applications 2. Middleware services

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 Application Design: Decentralized! What about: Distributed management control? Fault tolerance in distributed, asynchronous systems? Termination detection? Communication costs? Security?

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 Decentralized B&B: Performance ProcessorsExecution time (h) B&B timeContraction time Communication (MB/h/p) %0.3% %5.2% %11.7% %2.3% %1.1%4.5

6/28/2015 TWIST 2000 Decentralized B&B: Fault Tolerance

6/28/2015 TWIST 2000 Decentralized B&B: Fault Tolerance

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 Centralized or Decentralized? 1. Applications 2. Middleware services

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 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.

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 Resource Discovery: Requirements Efficient Accurate Secure No global hierarchy Politically difficult for wide area (impossible?) Hierarchical structures are resistant to change

6/28/2015 TWIST 2000 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 …

6/28/2015 TWIST 2000 Globus’ MDS – Step 1 C=US, o=Globus, o=ANL, ou=MCS C=US, o=Globus, o=USC, ou=ISI C=US, o=Globus, o=UC, ou=CS

6/28/2015 TWIST 2000 Globus’ MDS: Step 2 C=US, o=Globus, o=UC, ou=CS C=US, o=Globus, o=ANL, ou=MCS C=US, o=Globus, o=USC, ou=ISI

6/28/2015 TWIST 2000 Globus’ MDS: Step 3 Organizational Server Organizational Server Organizational Server o=Grid, dc=mcs, dc=anl, dc=gov o=Grid, dc=isi, dc=edu o=Grid, dc=cs, dc=uchicago, dc=edu Index Server A1 Index Server A2

6/28/2015 TWIST 2000 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

6/28/2015 TWIST 2000 Conclusions Applications running on collections of Internet-connected resources: may be centralized or decentralized. Middleware services must be decentralized.