Naming

Naming Entities

• A name in a distributed system is a string of bits or characters that is used to refer to an entity 
• Type of names
• Address
• The name of an access point of an entity
• Identifiers
• A name that uniquely identifies an entity
• Location-independent name
• A name that is independent from its addresses

Name Resolution

• A naming system maintains a name-to-address binding for resources
• Main problem in naming
• How to do name resolution in a distributed systems in a scalable way
• Approaches for name resolution closely tied to naming scheme
• Flat vs Structure naming
• In a flat name space, identifiers are random bit strings
• No information on location embedded in name

Name Resolution in a Flat Name Space

• Simple solutions that work in a LAN environment
• Broadcasting & Multicasting
• Message containing identifier of the entity is boardcast
• Machine with access point for the entity replies with the address of the access point
• ARP protocol for finding the data-link address of a machine given the IP address
• When network grows, multicast is more efficient
• Forwarding pointers
• When an entity moves from A to B, it leaves behind a reference to its new location at B
• Home-based Approaches
• Home agent keeps track of current location of mobile entity
• Hierarchical Approaches
• Similar to DNS

What is a DHT

• Distributed Hash Table
• key = hash(data)
• lookup(key) -> IP address
• send-RPC(IP address, PUT, key, value)
• Send-RPC(IP address, GET, key)  -> value
• Chord

Structure Naming Systems

• Names are organized into name spaces
• A name space can be represented as a labeled, directed graph wit two types of nodes
• Leaf nodes and directory nodes
• Absolute vs relative path names
• Local names vs global names
• Name resolution: the process of looking up a name
• Closure mechanism
• Knowing where and how to start name resolution
• Unix File Name Spaces

Linking and Mounting

• Symbolic link

• Mounting remote name spaces

Implementing Name Spaces

• Naming service
• A service that allows users and processes to add, remove, and lookup names
• Name spaces for large-scale widely distributed systems are typically organized hierarchically
• Three layers used to implement such distributed name spaces
• Global layer
• root node and its children
• Administrational layer
• Directory nodes within a single organization
• Managerial layer
• Example: DNS name space

Iterative vs Recursive Resolution

• Recursive

• puts a higher performance demand on each name server
• cons
• Too high for global layer name servers
• Pros
• Caching is more effective
• Communication costs may be reduces
• Example

• Iterative
• Example

Attribute-based Naming

• An entity is described in terms of (attribute, value) pairs
• Each entity can have several attributes
• Attribute-based naming service are called directory services
• LDAP (Lightweight directory access protocol) defacto industry standard
• Based on OSI X.500 directory service
• Another example: UDDI for web services