CS 603 Naming in Distributed Systems

1
CS 603Naming in Distributed Systems

• January 28, 2002

2
This weekNaming in Distributed Systems

• Today Overview
• What is a name
• Issues
• Examples
• Wednesday and Friday Name Resolution
• Historical (Telephone, mail, )?
• DNS?
• DCE?
• Others?

3
What is a name?

• An identifier that
• Identifies a resource
• Uniquely?
• Describes the resource?
• Enables us to locate that resource
• Directly?
• With help?
• Is it really an identifier?
• Bijective, persistent

4
Key issues in Naming

• How is name used?
• Disambiguate only
• Access resource given the name
• Build a name to find a resource
• Do humans need to use name?
• Construct?
• Recall?

5
Key issues in Naming (cont.)

• Is resource static?
• Never moves
• Change in location should change name
• Resource may move
• Resource is mobile
• Performance requirements

6
Approaches to naming

• Globally unique identifier
• Ethernet
• Solves identification, but not description or
  location
• Hierarchically assigned globally unique
  identifier
• Telephone number, IP address
• Solves identification, not description
• Helps with location

7
Approaches to naming

• Hierarchically assigned name
• Domain Name Service, URL
• Solves identification
• Helps with description
• Still problems with location
• Globally unique name
• TCP/IP Protocol Ports
• Extensibility problems

8
Approaches to naming

• Registries and name spaces
• Uniform Resource Name (URN)
• Solves identification and location
• If we can get to the registry
• Helps with description
• Registry can describe in detail
• Complicated!

9
URI, URL, URN

• URI Uniform Resource Identifier
• IETF meta-standard
• Defines naming schemes / protocols
• Each naming scheme has its own mechanism
• URL Uniform Resource Locator
• Uses DNS to map to host
• Host knows how to map remainder to resource
• URN Uniform Resource Name
• Idea Permanent URL

10
URN

• Each URN maps to a namespace
• Currently 10 formally defined IETF, ISBN,
  XMLORG,
• Also informal (3 current) and experimental
  (unregistered)
• Syntax urn ltNamespace IDgt ltstringgt
• urnISBN0-13-032071-4
• urnietfrfc2141
• (Bad) Example
• URNltassigned numbergtltFQDNgtltassigned stringgt
• urnx-1234www.cs.purdue.edu7eclifton2Fcs6032f

11
Naming Why an Issue for Application Developers?

• DNS is widely accepted standard
• Only names machines
• Doesnt handle mobility
• URI / URN will become standard
• Can be descriptive
• Globally unique
• Persistent
• But expensive to create

12
Applications that might need custom solutions

• Distributed Database
• Needs persistence
• May be multiple resources for single name
  (replication)
• May need to support mobility
• PERFORMANCE!
• Small-scale applications
• Do you really want to register with IANA?
• Is persistence necessary?

13
Distributed Database Example R

• R developed at IBM Almaden Research first
  distributed relational database
• Wanted mobility of resources
• Supports fault tolerance
• But movement rare
• Performance is critical
• Solution Two components to name
• Unique ID assigned by birthplace
• Local catalog maps ID to
• Birthplace (maintains current location)
• Presumed current location

14
Security Considerations

• Does name give away information?
• Social Security Numbers
• URL
• Batched IDs (e.g., Ethernet)
• Sequentially assigned IDs
• Solution Define what name SHOULD do
• Ensure it meets goals
• Look for reasons it doesnt

15
Name ResolutionWhat would you like?

• Historical?
• Mail
• Telephone
• DNS?
• X.500 / LDAP?
• DCE?
• ActiveDirectory?