NAME SERVICES Name Services From Chapter 9 of

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NAME SERVICES Name Services From Chapter 9 of Distributed Systems Concepts and Design, 4

NAME SERVICES Name Services From Chapter 9 of Distributed Systems Concepts and Design, 4 th Edition, By G. Coulouris, J. Dollimore and T. Kindberg Published by Addison Wesley/Pearson Education June 2005 1

NAME SERVICES Topics • Introduction • Name Services and the Domain Name System Couloris,

NAME SERVICES Topics • Introduction • Name Services and the Domain Name System Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 2

NAME SERVICES Introduction § In a distributed system, names are used to refer to

NAME SERVICES Introduction § In a distributed system, names are used to refer to a wide variety of resources such as: Ø Computers, services, remote objects, and files, as well as users. § Basic design issues for name services, such as the structure and management of the spaces of names recognized by the service and the operations that the name service supports, are outlined and discussed in the context of the Internet Domain Name Service. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 3

NAME SERVICES Introduction § Resources are accessed using identifier or reference Ø An identifier

NAME SERVICES Introduction § Resources are accessed using identifier or reference Ø An identifier can be stored in variables and retrieved from tables quickly. Ø Identifier includes or can be transformed to an address for an object. v E. g. NFS file handle, Corba remote object reference. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 4

NAME SERVICES Introduction Ø A name is human-readable value (usually a string) that can

NAME SERVICES Introduction Ø A name is human-readable value (usually a string) that can be resolved to an identifier or address. v Internet domain name, file pathname, process number v E. g. /etc/passwd, http: //www. cdk 3. net/ Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 5

NAME SERVICES Introduction § For many purposes, names are preferable to identifiers Ø The

NAME SERVICES Introduction § For many purposes, names are preferable to identifiers Ø The binding of the named resource to a physical location is deferred and can be changed. Ø They are more meaningful to users. § Resource names are resolved by name services Ø To give identifiers and other useful attributes. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 6

NAME SERVICES Introduction URL http: //www. cdk 3. net: 8888/Web. Examples/earth. html DNS lookup

NAME SERVICES Introduction URL http: //www. cdk 3. net: 8888/Web. Examples/earth. html DNS lookup Resource ID (IP number, port number, pathname) 138. 37. 88. 61 8888 Web. Examples/earth. html ARP lookup file (Ethernet) Network address 2: 60: 8 c: 2: b 0: 5 a Socket Web server Figure 1. Composed naming domains used to access a resource from a URL Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 7

NAME SERVICES Name Services and the Domain Name System § A name service stores

NAME SERVICES Name Services and the Domain Name System § A name service stores a collection of one or more naming contexts, sets of bindings between textual names and attributes for objects such as computers, services, and users. § The major operation that a name service supports is to resolve names. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 8

NAME SERVICES Name Services and the Domain Name System § DNS supports a model

NAME SERVICES Name Services and the Domain Name System § DNS supports a model known as iterative navigation. (Figure 2) Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 9

NAME SERVICES Name Services and the Domain Name System NS 2 2 Client 1

NAME SERVICES Name Services and the Domain Name System NS 2 2 Client 1 NS 1 Name servers 3 NS 3 A client iteratively contacts name servers NS 1–NS 3 in order to resolve a name Figure 2. Iterative navigation Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 10

NAME SERVICES Name Services and the Domain Name System § Reason for NFS iterative

NAME SERVICES Name Services and the Domain Name System § Reason for NFS iterative name resolution: Ø This is because the file service may encounter a symbolic link (i. e. an alias) when resolving a name. A symbolic link must be interpreted in the client’s file system name space because it may point to a file in a directory stored at another server. The client computer must determine which server this is, because only the client knows its mount points. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 11

NAME SERVICES Name Services and the Domain Name System § DNS offers recursive navigation

NAME SERVICES Name Services and the Domain Name System § DNS offers recursive navigation as an option, but iterative is the standard technique. § Recursive navigation must be used in domains that limit client access to their DNS information for security reasons. (Figure 3) Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 12

NAME SERVICES Name Services and the Domain Name System NS 2 2 2 client

NAME SERVICES Name Services and the Domain Name System NS 2 2 2 client 1 4 NS 1 client 3 1 NS 1 4 5 NS 3 Non-recursive server-controlled 3 Recursive server-controlled Figure 3. Non-recursive and recursive server-controlled navigation Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 13

NAME SERVICES Name Services and the Domain Name System § DNS - The Internet

NAME SERVICES Name Services and the Domain Name System § DNS - The Internet Domain Name System Ø DNS is a distributed naming database. Ø The arrangement of some of the DNS database is shown in Figure 4. Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 14

NAME SERVICES Name Services and the Domain Name System a. root-servers. net (root) ns

NAME SERVICES Name Services and the Domain Name System a. root-servers. net (root) ns 1. nic. au (au) Note: Name server names are in italics, and the corresponding domains are in parentheses. Arrows denote name server entries com. au edu. au. . . au purdue. edu yahoo. com. . ns. purdue. edu (purdue. edu) ns 0. ja. net (edu. au) *. purdue. edu usyd. edu. au authoritative path to lookup: raj-pc. csse. unimelb. edu. au abc. unimelb. edu. au (unimelb. edu. au) csse. unimelb. edu. au *. unimelb. edu. au. . . mulga. csse. unimelb. edu. au dns 0 -doc. usyd. edu. au (csse. unimelb. edu. au) (usyd. edu. au) *. csse. unimelb. edu. au *. usyd. edu. au Figure 4. DNS name servers Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 15

NAME SERVICES Name Services and the Domain Name System § Zone data are stored

NAME SERVICES Name Services and the Domain Name System § Zone data are stored by name servers in files in one of several fixed types of resource record. (Figure 5) Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 16

NAME SERVICES Name Services and the Domain Name System Record type Meaning Main contents

NAME SERVICES Name Services and the Domain Name System Record type Meaning Main contents A NS CNAME SOA WKS PTR IP number Domain name for server Domain name for alias Parameters governing the zone List of service names and protocols Domain name HINFO A computer address An authoritative name server The canonical name for an alias Marks the start of data for a zone A well-known service description Domain name pointer (reverse lookups) Host information MX TXT Mail exchange Text string Machine architecture and operating system List of < Arbitrary text Figure 5. DNS resource records Couloris, Dollimore and Kindberg Distributed Systems: Concepts & Design Edn. 4 , Pearson Education 2005 17

First Name Last Name First Name Last NameFirst Name Last Name First Name Last Name
Organizational Chart Name Title Name Name Title NameOrganizational Chart Name Title Name Name Title Name
First Name Last Name First Name Last NameFirst Name Last Name First Name Last Name
First Name Last Name First Name Last NameFirst Name Last Name First Name Last Name
First Name Last Name First Name Last NameFirst Name Last Name First Name Last Name
Strip Name Strip Name Strip Name Strip NameStrip Name Strip Name Strip Name Strip Name
company name company name company name company namecompany name company name company name company name
Name Services Johanna Hultin Carina Hglund Name servicesName Services Johanna Hultin Carina Hglund Name services
Chapter Rules Checklist Article I Name Chapter nameChapter Rules Checklist Article I Name Chapter name
Project Overview Project Name Company Name Presenter NameProject Overview Project Name Company Name Presenter Name
type name type name new typesize type nametype name type name new typesize type name
Use case name First Name Last Name OrganisationUse case name First Name Last Name Organisation
Top Table Name 1 Name 2 Name 3Top Table Name 1 Name 2 Name 3
String name x get Name y set NameString name x get Name y set Name
Introduction to Yugwa Team Name Name 1 NameIntroduction to Yugwa Team Name Name 1 Name
Project Overview Project Name Company Name Presenter NameProject Overview Project Name Company Name Presenter Name