1. COMP 655: Distributed/Operating Systems Summer 2011 Dr. Chunbo Chu Week 5: Naming 10/12/20151Distributed Systems - COMP 655

2. 10/12/2015Distributed Systems - Comp 6552 What is the naming problem? Name objects in distributed systems so that the naming system provides 1.Human-friendly names for use by people 2.System-friendly names for use by systems 3.Uniqueness where necessary 4.Ambiguity when helpful 5.A service that can be used in many systems 6.Minimal centralized administration 7.Global scalability

3. 10/12/2015Distributed Systems - Comp 6553 Ambiguity when useful www.yahoo.akadns.net27 A216.109.118.78 www.yahoo.akadns.net27 A216.109.118.64 www.yahoo.akadns.net27 A216.109.118.65 www.yahoo.akadns.net27 A216.109.118.66 www.yahoo.akadns.net27 A216.109.118.72 www.yahoo.akadns.net27 A216.109.118.73 www.yahoo.akadns.net27 A216.109.118.74 www.yahoo.akadns.net27 A216.109.118.76

4. 10/12/2015Distributed Systems - Comp 6554 Aspects of human-friendliness What do humans need in the names they use?

5. 10/12/2015Distributed Systems - Comp 6555 Examples of human-friendly names Albert Einstein einstein cs.franklin.edu franklin.edu edu http://cs.franklin.edu/~chuc/655/ /home/export/cs/Htdocs/Syllabus/comp655/

6. 10/12/2015Distributed Systems - Comp 6556 Types of system-friendly names Addresses Identifiers Brainstorm What are identifiers, addresses?

7. 10/12/2015Distributed Systems - Comp 6557 Address Definition – a name that refers to an access point in a communication system Examples –swartoud@franklin.edu –205.133.198.15:1677 –00-04-E2-36-A0-5E –201 S. Grant Avenue, Columbus, Ohio 43215 –614-797-4700 –877-341-6300

8. 10/12/2015Distributed Systems - Comp 6558 Definition Identifier – a name with the following properties: 1.It refers to at most one entity 2.An entity has at most one identifier 3.Once used for one entity, its meaning never changes -- Tanenbaum, Page 181

9. 10/12/2015Distributed Systems - Comp 6559 Examples of identifiers {72eb61e0-8672-4303-9175-f2e4c68b2e7c} {b4431a67-9e32-4e2d-81e5-076a5f1b6170} 6a29b0a6b9ad79c8:f72617:ff5c75073e:-7ffd 00-04-E2-36-A0-5E 123-45-6789 (close to being an identifier)

10. 10/12/2015Distributed Systems - Comp 65510 Globally Unique Identifiers (GUIDs) DCE/Microsoft: A GUID is a 128-bit integer (16 bytes) that can be used across all computers and networks wherever a unique identifier is required. Such an identifier has a very low probability of being duplicated. GUIDs are generated using a combination of the current date and time, a counter, and the MAC address from the network card.

11. 10/12/2015Distributed Systems - Comp 65511 UIDs in Java new java.rmi.server.UID() –f72617:ff5c75073e:-7ffc Javadocs say: A UID instance contains three primitive values: –unique, an int that uniquely identifies the VM that this UID was generated in –time, a long equal to a time (as returned by System.currentTimeMillis() ) at which the VM that this UID was generated in was alive System.currentTimeMillis() –count, a short to distinguish UID s generated in the same VM with the same time value

12. VMIDs in Java A VMID is a identifier that is unique across all Java virtual machines. VMIDs are used by the distributed garbage collector to identify client VMs. new java.rmi.dgc.VMID() –6a29b0a6b9ad79c8:f72617:ff5c75073e:-7ffd –Adds an address to the UID. 10/12/2015Distributed Systems - Comp 65512

13. 10/12/2015Distributed Systems - Comp 65513 If you remember nothing else Distributed systems use three kinds of names: –Human-friendly names –Addresses –Identifiers Naming services manage the associations among these kinds of names.

14. 10/12/2015Distributed Systems - Comp 65514 What about part 7 of the naming problem (global scalability)?

15. 10/12/2015Distributed Systems - Comp 65515 Easy naming Directory service in our projects Only notebooks are named Notebook names are arbitrary character strings – no formation rules Light usage –A handful of names –Busy minute: a few dozen transactions Usually on a LAN

16. 10/12/2015Distributed Systems - Comp 65516 Hard naming – the Web Global scalability –Millions of entities to name –Millions of name lookups per hour –Slow and expensive communications –Many independently-administered domains Location-related transparency –Location –Re-location –Migration –Replication

17. 10/12/2015Distributed Systems - Comp 65517 Definition Name – a string of characters or bits that refers to something –Names in a computer system conform to some set of formation rules –Names have semantics that determine how a name maps to a thing –Some names have to be obtained from a naming authority

18. 10/12/2015Distributed Systems - Comp 65518 Name space directory table root node path name (“absolute”) relative path name: steen/.twmrc global path name: nfs://flits/home/steen/.twmrc

19. 10/12/2015Distributed Systems - Comp 65519 Another name space: Java packages and classes dino.naming.NameChooser java.rmi.server. ObjID dino/naming/NameChooser.class java/rmi/server/ObjID.class

20. 10/12/2015Distributed Systems - Comp 65520 Yet another name space: DNS names ::= | " " ::= | "." ::= [ [ ] ] ::= | ::= | "-" ::= | ::= any one of the 52 alphabetic characters A through Z in upper case and a through z in lower case ::= any one of the ten digits 0 through 9 Source: RFC-1035 RFC-1035

21. 10/12/2015Distributed Systems - Comp 65521 Three layers of DNS names Top-level domains DNS supports top 2 levels local file system

22. Distributed Systems - COMP 655 Name Space Distribution (2) 10/12/201522

23. 10/12/2015Distributed Systems - Comp 65523 Semantics - name resolution Given a name, look up information about the entity the name refers to In a hierarchical namespace, resolution works by: –Picking a starting point –Working down, across, or up the hierarchy from there A closure mechanism is a way of deciding where to start name resolution –For local absolute names: where’s the root node? –For relative names: where’s the current node? –For global names: which root node?

24. 10/12/2015Distributed Systems - Comp 65524 Resolution implementation Name resolution for common name spaces is usually an operating system function –File system names –DNS names

25. 10/12/2015Distributed Systems - Comp 65525 Namespace collaboration Linking Mounting Composite names Abstract naming system interfaces

26. 10/12/2015Distributed Systems - Comp 65526 Linking Aliases (aka synonyms) –Hard links (multiple absolute paths to the same entity) –Symbolic links (leaf nodes contains an absolute path to the entity) Beware of cycles Symbolic links often integrate smoothly into distributed systems –hard links cannot be made between files on different file systems nor between directories

27. Distributed Systems - COMP 655 Linking 10/12/201527

28. 10/12/2015Distributed Systems - Comp 65528 Mounting Mounting == allowing a directory node to store the identifier of a directory node in some other namespace Mount point == the local directory node Mounting point == the remote directory node –For UNIX file systems, mounting point is usually a root node –For Windows file systems, mount point is usually a root node (example – G: drive maps to \\randomserver\games)

29. Distributed Systems - COMP 655 Mounting Information required to mount a foreign name space in a distributed system The name of an access protocol. The name of the server. The name of the mounting point in the foreign name space. 10/12/201529

30. Distributed Systems - COMP 655 Linking and Mounting 10/12/201530

31. 10/12/2015Distributed Systems - Comp 65531 Composite names Include the three essentials in one string: ftp: //ftp.cs.vu.nl/home/steen/mbox protocolserver resource name (in remote name space) http: //cs.franklin.edu/~chuc /655/

32. 10/12/2015Distributed Systems - Comp 65532 Composite names in the Java RMI Registry //einstein:4310/SuperTalk //:4321/Inventory //einstein.franklin.edu/Mfg //192.70.252.120:4300/chat //host:port/servicename Structure Examples

33. 10/12/2015Distributed Systems - Comp 65533 Iterative name resolution Resolving ftp://ftp.cs.vu.nl NOTE: client’s name resolver may not run on the client machine. It may also be a name server for local entities

34. 10/12/2015Distributed Systems - Comp 65534 Recursive name resolution Resolving ftp://ftp.cs.vu.nl

35. 10/12/2015Distributed Systems - Comp 65535 Compare & contrast Advantages of recursive resolution: –Name servers can cache addresses of lower- level nodes –Usually, fewer long-haul communications Disadvantage of recursive resolution: –Higher-level name servers can become bottlenecks

36. Distributed Systems - COMP 655 Example: The Domain Name System 10/12/201536

37. 10/12/2015Distributed Systems - Comp 65537 Name service clients Embedded in applications –Web browsers –Email servers –Email clients –ftp, ssh, etc Command line –nslookup –dig

38. 10/12/2015Distributed Systems - Comp 65538 nslookup types on p. 202, cs.vu.nl table on p. 205 $ nslookup Default Server: ns1.franklin.edu Address: 192.70.252.125 > set type=ANY > cs.vu.nl Server: ns1.franklin.edu Address: 192.70.252.125 Non-authoritative answer: cs.vu.nl nameserver = top.cs.vu.nl cs.vu.nl nameserver = solo.cs.vu.nl cs.vu.nl nameserver = star.cs.vu.nl cs.vu.nl nameserver = ns.vu.nl Authoritative answers can be found from: cs.vu.nl nameserver = solo.cs.vu.nl cs.vu.nl nameserver = star.cs.vu.nl cs.vu.nl nameserver = ns.vu.nl cs.vu.nl nameserver = top.cs.vu.nl top.cs.vu.nl internet address = 192.31.231.43 solo.cs.vu.nl internet address = 130.37.24.1

39. 10/12/2015Distributed Systems - Comp 65539 dig To find: Google dig dns download

40. 10/12/2015Distributed Systems - Comp 65540 Codd on dig

41. 10/12/2015Distributed Systems - Comp 65541 JNDI http://java.sun.com/products/jndi/ http://java.sun.com/products/jndi/servi ceproviders.htmlhttp://java.sun.com/products/jndi/servi ceproviders.html

42. 10/12/2015Distributed Systems - Comp 65542 Summary: naming system patterns Hierarchical namespace Independent administration of sub-trees Symbolic links Synonyms Name includes the name of an interpretative system