Remote Procedure Call Practical Issues

1. Remote Procedure CallPractical Issues CS-4513Distributed Computing Systems (Slides include materials from Operating System Concepts, 7th ed., by Silbershatz, Galvin, & Gagne, Modern Operating Systems, 2nd ed., by Tanenbaum, and Distributed Systems: Principles & Paradigms, 2nd ed. By Tanenbaum and Van Steen) Practical Issues of RPC

2. Review • Message-oriented communication • Connections • Establishing a connection with a service • Reliable communication via TCP • Connection-less communication via UDP • Remote Procedure Call • Procedural interface between client and service • IDL & stub compiler (hides communication details) • Hiding data representation differences • Restrictions on passing objects by reference Practical Issues of RPC

3. Practical RPC Systems • DCE (Distributed Computing Environment) • Open Software Foundation • Basis for Microsoft DCOM • Tanenbaum & Van Steen, §4.2.4 • Sun’s ONC (Open Network Computing) • Very similar to DCE • Widely used • rpcgen • http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-Q0R5B-TET1_html/TITLE.html Practical Issues of RPC

4. Practical RPC Systems (continued) • Java RMI (Remote Method Invocation) • java.rmi standard package • Java-oriented approach — objects and methods • CORBA (Common Object Request Broker Architecture) • Standard, multi-language, multi-platform middleware • Object-oriented • Heavyweight • … Practical Issues of RPC

5. Implementation Model for DCE Practical Issues of RPC

6. Differences for ONC program & version # program & version # rpcgen Practical Issues of RPC

7. Validating a Remote Service • Purpose • Avoid binding to wrong service or wrong version • DCE • Globally unique ID • Generated in template of IDL file • Sun ONC • Program numbers registered with Sun • Version # and procedure # administered locally Practical Issues of RPC

8. RPC Binding — Sun ONC • Service registers with portmapper on server OS • Program # and version # • Optional static port # • Client • Must know host name or IP address • clnt_create(host, prog, vers, proto) • I.e., RPC to portmapper of host requesting to bind to prog, vers using protocol proto (tcporudp) • (Additional functions for authentication, etc.) • Invokes remote functions by name Practical Issues of RPC

9. Sun ONC (continued) • #include <rpc/rpc.h> • Header file for client and server • rpcgen • The stub compiler • Compiles interface.x • Produces .h files for client and service; also stubs • See also • rpcinfo • RPC Programming Guide Practical Issues of RPC

10. Note on XDR(the interface definition language for ONC) • Much like C • Exceptions • string type – maps to char * • bool type – maps to bool_t Practical Issues of RPC

11. Sun ONC • Online tutorial • http://h30097.www3.hp.com/docs/base_doc/DOCUMENTATION/HTML/AA-Q0R5B-TET1_html/TITLE.html • CS-4513 code samples • http://web.cs.wpi.edu/~rek/DCS/D04/SunRPC.html • http://web.cs.wpi.edu/~goos/Teach/cs4513-d05/ • http://web.cs.wpi.edu/~cs4513/b05/week4-sunrpc.pdf • Any other resources you can find Practical Issues of RPC

12. Java RMI • Based on objects & methods • I.e., an object may be located remotely • Accessed via methods • RMI causes methods to be invoked by RPC • Stubs may be local or remote • Subject to security policy Practical Issues of RPC

13. Java RMI Binding • Remote objects must be registered with RMI registry • May specify a port • Security policy compiled with object • Client looks up object via Naming method • Specifies host (& port, if needed) • Remote stubs delivered with lookup, subject to security policy Practical Issues of RPC

14. Java Remote Object details • Interface must extend java.RMI.Remote • Must be public • No new methods introduced by java.RMI.Remote • Should also extend • java.rmi.server.UnicastRemoteObject • Replaces some Object class methods for proper operation in distributed environment • Must throw java.rmi.RemoteException • May impact definition of existing interfaces Practical Issues of RPC

15. Java Remote Object details (continued) • Compiling object and stubs • Object compiled to bytecodes with javac • Stubs compiled with rmic • RMI registry must be running before remote object can be launched • rmiregistry command (part of JDK distribution) • Multiple registries possible on different ports • Remote object registers itself • java.rmi.Naming interface Practical Issues of RPC

16. Java Client details • Initialize RMI security manager • System.setSecurityManager(…) • If no security manager, only local stubs may be loaded • Client must find and bind to remote object • lookup() method in java.RMI.Naming • Location of remote object specified in URL style • E.g., “rmi://garden.wpi.edu:1099/ObjectName” • Remote stubs loaded by lookup • Per security policy Practical Issues of RPC

17. Java RMI • CS-4513 examples • http://web.cs.wpi.edu/~cs4513/b05/week4-javarmi.pdf • http://web.cs.wpi.edu/~goos/Teach/cs4513-d05/ • http://web.cs.wpi.edu/~rek/DCS/D04/Comm_Part2.pdf • Uses terms “proxy” and “skeleton” for “client-side stub” and “service-side stub” respectively • Identifies issues with SYNCHRONIZED remote objects • Tanenbaum & Van Steen • §10.3, esp. §10.3.4 • Any other resources you can find Practical Issues of RPC

18. Questions? Practical Issues of RPC

19. Fundamental Issue • With Sun ONC and Java RMI, client must know name or address of server machine in order to bind to remote service • IP address or remote name • (Sometimes) port number • I.e., services are bound to server machines Practical Issues of RPC

20. Problems • Location of remote objects not always known • Location of remote objects not always constant • Pointers/References to remote services are only useful to fixed servers • Distributed & replicated services are difficult, at best • Location independence is impossible • … Practical Issues of RPC

21. Needed • Location-independent object registry • Any object can register itself • Location-independent object naming • Name of object does not imply location • Distributed, replicated registry • If any instance goes down, others can serve • Distributed, replicated remote objects • Any instance may serve in many cases • … Practical Issues of RPC

22. Solutions • Some or all of these things are typically provided in the major distributed object standards • DCOM, CORBA, etc. • “Global” registry is central component Practical Issues of RPC

23. But … • None really get it right for broad spectrum of distributed systems & applications • E.g., CORBA • Very heavyweight (too cumbersome) • Object can live in only one location • Inefficient for very commonly accessed objects • Distributed, replicated object difficult to support Practical Issues of RPC

24. Reading Assignment • “Grapevine: An Exercise in Distributed Computing,” Communications of the ACM, April 1982 • PDF link Practical Issues of RPC

25. Break Practical Issues of RPC