Metacomputing Directory Service (MDS)

A Directory Service for Configuring High-Performance Distributed Computations (Fitzgerald et. al.) Joel Thomas

Overview

 Introduction  Design Considerations  Current Approaches  Design of MDS  Implementation  MDS With Globus  Future  Conclusion

Introduction

 High performance distributed computing requires selection, configuration  To make good decisions, timely, accurate information is invaluable  Currently, have nonstandard ways to store/access the right kind of data  The Metacomputing Directory Service (MDS) hopes to provide a scalable service to handle this need

Design Considerations

 Performance  Scalability and cost  Uniformity  Expressiveness  Extensibility

Design Considerations(cont.)

 Multiple Information Sources  Dynamic data  Flexible access  Security  Deployability  Decentralized maintenance

Current Approaches

 Uname, sysinfo  Simple Network Management Protocol(SNMP), NIS(Network Information Service)  PVM(Parallel Virtual Machine), MPICH (Message Passing Interface)  DNS (Domain Name Service)  X.500, LDAP (Lightweight Directory Access Protocol)  Chose to integrate existing systems as much as possible  But use LDAP to organize

Design of MDS

 Representation and Data Access  Data Model  Implementation

Representation

 Borrows straight from LDAP  Entry: instance of person, network, computer, etc.

 Type is created by associating an object class  Directory Information Tree (DIT)  hierarchical, tree-structured name space  Distinguished Name (DN)  path from leaf to root entry 

ou = MCS, o = Argonne National Laboratory, o = Globus, c = US >

DIT example

Object Classes

 LDAP has set of standard class definitions, which can be extended (top, group classes, etc.)  Defines attributes for an entry, and what values those attributes may contain  Attributes may be required or optional  Can use inheritance to build new classes

Data Model

 Consists of DIT hierarchy and object class definitions  Computer centric, not network centric  People, hosts, communication networks under organization

Data Model (cont.)

 GlobusHost  GlobusNetwork  Link protocol (ATM, Ethernet)  Network topology(bus, ring)  Physical media (copper, fiber)  GlobusNetworkInterface  Physical characteristics (speed) and hardware address  Hosts contain network interfaces  Network interfaces attached to networks

Configuration example

MDS representation

Data Model (cont.)

 Physical vs. Logical Network info  Single network, multiple protocol stacks   Each may have distinct interface and performance Images: multiple logical views of the same physical network (RFC 1609)  contains new information, and pointer back to physical  Physical has reference to all images that point to it  GlobusHostImage  GlobusNetworkImage  GlobustNetworkInterfaceImage

Implementation

 While LDAP interface met most needs, default implementation was somewhat slow  Problems:  Single information provider  Client/server architecture  Scope of Data  Allows info providers to provide information per attribute  Time to Live (TTL) for attribute (before refreshing)  Update scope: process, computation, global

Sample queries

 What are the network interfaces for ATM?

 Find GlobusNetworkInterface->GlobusNetwork (link_protocol=ATM)  For that GNI, GlobusNetworkInterface >GlobusNetworkInterfaceImage (ip_address)  Which nodes can use vendor protocols on fast internal networks?

 Two GlobusHostImages belong to the same GlobusNetworkImage object

MDS Recap

MDS with Globus

 Nexus communication module  Uses MDS to find out what low-level mechanisms are between modules  Select between mechanism, based on rules  Rules based on dynamic information or programmer preference  Code runs unchanged, but can adapt to meet performance needs  I-WAY TestBed (heterogeneous virtual machines)  Resource Location  Resource Brokers

Future

 Use in GUSTO  Extend Globus components to use MDS  Expand information sources  Optimize for common operations  Sophisticated applications (e.g. resource scheduling)  Performance metrics

Conclusion

 Designed to provide dynamic information in a timely, scalable manner  Take advantage of LDAP flexibility and growing usage in industry  Provide information richness in extensible manner