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Naming in Distributed Systems

Naming in Distributed Systems. Outline. Introduction Some basic Concepts INS :) Yet another naming Scheme. Why Name?. Convenience in Accessing/Sharing Objects (Files) Fundamental concept in Communication (mailboxes, remote nodes). What does Naming get us?.

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Naming in Distributed Systems

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  1. Naming in Distributed Systems

  2. Outline • Introduction • Some basic Concepts • INS :) • Yet another naming Scheme.

  3. Why Name? Convenience in Accessing/Sharing Objects (Files) Fundamental concept in Communication (mailboxes, remote nodes)

  4. What does Naming get us? • Mapping between names->objects • Provide info on those objects • Locate/discover objects and their attributes Thus it directly affects : • Sharing, migration, replication, security

  5. Names • Most definitions are inadequate. • ISO : It is an identifier that denotes an object. Classification • Non-Ambiguous. 1->N (Name->Object) • Non-Unique. N->1 • Global.

  6. Names, Addresses And Routes • Name specifies WHAT, address WHERE, routes HOW to get there. • Each is a tighter binding of information. • System names / Communication names. • Name is usually user-friendly. Naming facility translates names-> addresses-> routes. Routing is part of naming!

  7. Name Structure • Flat : No internal structure. • Partitioned : Usually hierarchical and have a naming context. • Descriptive : Attribute Based. Partitioned name is subclass. Non-unique Names. Std. Structure & Semantics needed.

  8. Naming Context/Domain • A context can be defined as the environment in which a name is valid. (Global names have no context.) • Helps partition the name space. • Implicit Context : Relative naming conventions.

  9. Naming schemes • Hierarchical : • Extensible/scalable. • Goes with logical view of the system. • Implicit context -> smaller names. • Configuration is (usually) not simple.

  10. Naming Schemes (cont’d) • Descriptive : • Supports ‘services’. • Scalable. • Easily supports fault-tolerance, group communication. • Processing overhead is usually large.

  11. Naming Schemes (cont’d) • Flat : • No internal structure. • Names remain same even if object moves. • Easily hashed and stored (no processing overhead) : efficient. • Easier to implement? • Not scalable.

  12. Factors in Designing Naming Facility • Ease of Name generation. • Location Transparency: Dynamic binding of names->addresses. Object mobility. • Two levels of identification : user-friendly, machine-friendly. • Efficient : Delay, #messages exchanged must be minimum.

  13. Support for 1->N mapping between names & addresses : • Fault Tolerance • Group Communication.

  14. INS • LCS, MIT. 1999 • Part of self-organizing adaptive networks research.

  15. Motivation • How to adapt to dynamicity in networks seamlessly - mobility of devices and services. • Dynamic resource discovery and service location. • Software and service mgmt cost > HW • E.g. : good ol’ printer, finding least loaded server, etc.

  16. Design Goals • Expressiveness : in finding/discovering devices/services. • Responsiveness : adapt quickly to mobility. • Robustness : Name service failures, inconsistent state. • Easy Configuration : minimal manual intervention, dynamic load distribution.

  17. What is meant by INS • Describe ‘what’ (intent) to look for, not where. • Intentional names implemented using name-specifiers :- Hierarchy of attributes and values. • Message headers contain name-specifiers not IP addresses.

  18. INS Architecture • INRs form overlay network. • Services register with the INRs (periodic advertisement) • Clients send messages to INRs. • Early/Late binding. • Intentional anycast/multicast.

  19. INR boot-up • DSR (Domain Space Resolver) maintains list of active/candidate INRs. • New INR : ping every other INR. Establish neighbour relation. • Spanning tree of INRs.

  20. Service Registration • Soft State, Soft State, Soft State! :- robustness. • Periodically advertise intentional names to INR. • INR relays names to other INRs periodically :- All INRs know all names!

  21. Client side • Intentional Anycast : Send to any server satisfying request. • Intentional Multicast : All servers satisfying request • Early Binding : Similar to DNS. • Late Binding : Message routing at name resolution time.

  22. Load Balancing, Scaling • Spawn INRs on candidates. Kill if below threshold. • Divide name-space : • Handle only part of name space. • Cache popular ones. • Refer to root (DSR) otherwise.

  23. Naming & Addressing withoutUnique Identifiers • Sony CSL. • Muse operating system.

  24. Motivation • Scalability. Ability to generate unique ids regardless how how big system grows. • Mobility : Of hosts and dynamically adapting to it.

  25. Design Goals • Uniqueness : One name should only represent one object. • Location transparency. • Scalability • Short repstn. to logically nearby objects. • Availability and fault tolerance of name service.

  26. Assumptions • Ultra large scale : broadcast impossible. • Communication with distant objects is rare compared to local ones. • Local naming contexts with hierarchical structure.

  27. Design • One root naming context • Relative representation. • OIDs, OADs, LIDs, LADs : • Format of OID. • Interpretation of OID • Translation of OID/OAD • Message Passing • Object Migration

  28. Close

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