Rpc Case Studies (Distributed computing)

RPC Case Studies Paul Krzyzanowski [email_address] [email_address] Distributed Systems Except as otherwise noted, the content of this presentation is licensed under the Creative Commons Attribution 2.5 License.

Overview of RPC Systems Sun RPC DCE RPC DCOM CORBA Java RMI XML RPC, SOAP/.NET, AJAX, REST

Sun RPC RPC for Unix System V, Linux, BSD, OS X Also known as ONC RPC (Open Network Computing) Interfaces defined in an Interface Definition Language ( IDL ) IDL compiler is rpcgen

RPC IDL Interface definition program number Interface definition version 1 version 2

RPC IDL program GETNAME { version GET_VERS { long GET_ID(string<50>) = 1; string GET_ADDR(long) = 2; } = 1; /* version */ } = 0x31223456; name.x

rpcgen rpcgen name.x produces: name.h header name_svc.c server stub (skeleton) name_clnt.c client stub [ name_xdr.c ] XDR conversion routines Function names derived from IDL function names and version numbers Client gets pointer to result Allows it to identify failed RPC (null return)

What goes on in the system: server Start server Server stub creates a socket and binds any available local port to it Calls a function in the RPC library: svc_register to register program#, port # contacts portmapper ( rpcbind on SVR4) : Name server Keeps track of {program#,version#,protocol}  port# bindings Server then listens and waits to accept connections

What goes on in the system: client Client calls clnt_create with: Name of server Program # Version # Protocol# clnt_create contacts port mapper on that server to get the port for that interface early binding – done once, not per procedure call

Advantages Don’t worry about getting a unique transport address (port) But with SUN RPC you need a unique program number per server Greater portability Transport independent Protocol can be selected at run-time Application does not have to deal with maintaining message boundaries, fragmentation, reassembly Applications need to know only one transport address Port mapper Function call model can be used instead of send/receive

DCE RPC DCE : set of components designed by The Open Group (merger of OSF and X/Open) for providing support for distributed applications Distributed file system service, time service, directory service, … Room for improvement in Sun RPC

DCE RPC Similar to Sun’s RPC Interfaces written in a language called Interface Definition Notation ( IDN ) Definitions look like function prototypes Run-time libraries One for TCP/IP and one for UDP/IP Authenticated RPC support with DCE security services Integration with DCE directory services to locate servers

Unique IDs Sun RPC required a programmer to pick a “unique” 32-bit number DCE: get unique ID with uuidgen Generates prototype IDN file with a 128-bit Unique Universal ID (UUID) 10-byte timestamp multiplexed with version number 6-byte node identifier (ethernet address on ethernet systems)

IDN compiler Similar to rpcgen: Generates header, client, and server stubs

Service lookup Sun RPC requires client to know name of server DCE allows several machines to be organized into an administrative entity cell (collection of machines, files, users) Cell directory server Each machine communicates with it for cell services information

DCE service lookup client cell dir server Request service lookup from cell directory server Return server machine name service? server

DCE service lookup client cell dir server Connect to endpoint mapper service and get port binding from this local name server local dir server SERVER service? port dced

DCE service lookup client cell dir server Connect to service and request remote procedure execution local dir server SERVER RPC server dced

Marshaling Standard formats for data NDR: Network Data Representation Goal Sender can (hopefully) use native format Receiver may have to convert

Sun and DCE RPC deficiencies If server is not running Service cannot be accessed Administrator responsible for starting it If a new service is added There is no mechanism for a client to discover this Object oriented languages expect polymorphism Service may behave differently based on data types passed to it

The next generation of RPCs Support for object oriented languages

Microsoft DCOM OLE/COM  DCOM: Windows NT 4.0, fall 1996 Extends Component Object Model (COM) to allow objects to communicate between machines

Activation on server Service Control Manager (SCM, part of COM library) Connects to server SCM Requests creation of object on server Surrogate process runs components Loads components and runs them Can handle multiple clients simultaneously

Beneath DCOM Data transfer and function invocation Object RPC ( ORPC ) Extension of the DCE RPC protocol Standard DCE RPC packets plus: Interface pointer identifier (IPID) Identifies interface and object where the call will be processed Referrals: can pass remote object references Versioning & extensibility information

Marshaling Marshaling mechanism: NDR (Network Data Representation) of DCE RPC One new data type: represents a marshaled interface

MIDL MIDL files are compiled with an IDL compiler DCE IDL + object definitions Generates C++ code for marshaling and unmarshaling Client side is called the proxy Server side is called the stub both are COM objects that are loaded by the COM libraries as needed

Remote reference lifetime Object lifetime controlled by remote reference counting RemAddRef , RemRelease calls Object elided when reference count = 0

Cleanup Abnormal client termination No message to decrement reference count set to server Pinging Server has pingPeriod , numPingsToTimeOut Relies on client to ping background process sends ping set – IDs of all remote objects on server If ping period expires with no pings received, all references are cleared

Microsoft DCOM improvements Fits into Microsoft COM Generic server hosts dynamically loaded objects Requires unloading objects (dealing with dead clients) Reference counting and pinging Support for references to instantiated objects But… DCOM is a Microsoft-only solution Doesn’t work well across firewalls

CORBA Common Object Request Architecture Evolving since 1989 Standard architecture for distributing objects Defined by OMG ( Object Management Group ) Consortium of >700 companies Goal : provide support for distributed, heterogeneous object-oriented applications Specification is independent of any language, OS, network

CORBA Basic paradigm : Request services of a distributed object Interfaces are defined in an IDL Distributed objects are identified by object reference Object Request Broker ( ORB ) delivers request to the object and returns results to the client = set of code that implements RPC

CORBA logical view object implementation client ORB Generated stub code Generated skeleton code

IDL ( Interface Definition Language ) Indicates operations an object supports Not how they are implemented Programming language neutral Currrently standardized language bindings for C, C++, Java, Ada, COBOL, Smalltalk, Objective C, LISP, Python IDL data types Basic types: long, short, string, float, … Constructed types: struct, union, enum, sequence Typed object references The any type: a dynamically typed value

IDL example Module StudentObject { struct StudentInfo { string name; int id; float gpa; }; exception Unknown {}; interface Student { StudentInfo getinfo(in string name) raises(Unknown); void putinfo(in StudentInfo data); }; };

CORBA IDL Compiled with IDL compiler Converted to target language Generates stub functions

Object Request Broker (ORB) Distributed service that implements the request to the remote object Locates the remote object on the network Communicates request to the object Waits for results Communicates results back to the client Responsible for providing location transparency Same request mechanism used by client & CORBA object regardless of object location Client request may be written in a different programming language than the implementation

ORB functions Look up and instantiate objects on remote machines Marshal parameters Deal with security issues Publish data on objects for other ORBs to use Invoke methods on remote objects Static or dynamic execution Automatically instantiate objects that aren’t running Route callback methods Communicate with other ORBs

Objects Object references persist They can be saved as as string … and be recreated from a string Client Performs requests by having an object reference for object & desired operation Client initiates request by calling stub routines specific to an object Or constructing request dynamically ( DII interface) Server (object implementation) Provides semantics of objects Defines data for instance, code for methods

Interoperability CORBA clients are portable They conform to the API … but may need recompilation Object implementations (servers) generally need some rework to move from one vendor’s CORBA product to another 1996: CORBA 2.0 added interoperability as a goal in the specification Define network protocol called IIOP Inter-ORB Protocol IIOP works across any TCP/IP implementations

IIOP IIOP can be used in systems that do not even provide a CORBA API Used as transport for version of Java RMI (RMI over IIOP) Various application servers use IIOP but do not expose the CORBA API Programs written to different APIs can interoperate with each other and with programs written to the CORBA API

CORBA Services ( COS ) Set of distributed services to support the integration and interoperation of distributed objects Defined on top of ORB Standard CORBA objects with IDL interfaces

Popular services Object life cycle Defines how CORBA objects are created, moved, removed, copied Naming Defines how objects can have friendly symbolic names Events Asynchronous communication Externalization Coordinates the transformation of objects to/from external media

Popular services Transactions Provides atomic access to objects Concurrency control Locking service for serializable access Property Manage name-value pair namespace Trader Find objects based on properties and describing service offered by object Query Queries on objects

CORBA vendors Lots of vendors ORBit Bindings for C, Perl, C++, Lisp, Pascal, Python, Ruby, and TCL (designed for GNOME) Java ORB Part of Java SDK VisiBroker for Java From Imprise; embedded in Netscape Communicator OrbixWeb From Iona Technologies Websphere From IBM Many, many others

Assessment Reliable, comprehensive support for managing services Standardized Complex Steep learning curve Integration with languages not always straightforward Pools of adoption Late to ride the Internet bandwagon

Java RMI Java language had no mechanism for invoking remote methods 1995: Sun added extension Remote Method Invocation ( RMI ) Allow programmer to create distributed applications where methods of remote objects can be invoked from other JVMs

RMI components Client Invokes method on remote object Server Process that owns the remote object Object registry Name server that relates objects with names

Interoperability RMI is built for Java only! No goal of OS interoperability (as CORBA) No language interoperability (goals of SUN, DCE, and CORBA) No architecture interoperability No need for external data representation All sides run a JVM Benefit: simple and clean design

RMI similarities Similar to local objects References to remote objects can be passed as parameters (not really) Objects can be passed as parameters to remote methods (but not as a reference) Object can be cast to any of the set of interfaces supported by the implementation Operations can be invoked on these objects

RMI differences Non-remote arguments/results passed to/from a remote method by copy Remote object passed by reference, not by copying remote implementation Extra exceptions

New classes remote class : One whose instances can be used remotely Within its address space: regular object Other address spaces: can be referenced with an object handle serializable class : Object that can be marshaled If object is passed as parameter or return value of a remote method invocation, the value will be copied from one address space to another If remote object is passed, only the object handle is copied between address spaces

New classes remote class : One whose instances can be used remotely Within its address space: regular object Other address spaces: can be referenced with an object handle serializable class : Object that can be marshaled If object is passed as parameter or return value of a remote method invocation, the value will be copied from one address space to another If remote object is passed, only the object handle is copied between address spaces needed for remote objects needed for parameters

Stubs Generated by separate compiler rmic Produces Stubs and skeletons for the remote interfaces are generated (class files)

Naming service Need a remote object reference to perform remote object invocations Object registry does this: rmiregistry

Server Register object(s) with Object Registry Stuff obj = new Stuff(); Naming.bind(“MyStuff”, obj);

Client Contact rmiregistry to lookup name rmiregistry returns a remote object reference. lookup gives reference to local stub. Invoke remote method(s): test.func(1, 2, “hi”); MyInterface test = (MyInterface) Naming.lookup(“rmi://www.pk.org/MyStuff”);

Java RMI infrastructure client application registry stub skeleton remote interface remote object implementation bind lookup remote reference f(args) f(args) return/exc. return/exception marshal stream

RMI Distributed Garbage Collection Two operations: dirty and free Local JVM sends a dirty call to the server JVM when the object is in use The dirty call is refreshed based on the lease time given by the server Local JVM sends a clean call when there are no more local references to the object Unlike DCOM: no incrementing/decrementing of references

The third generation of RPCs Web services and Riding the XML Bandwagon

We began to want Remotely hosted services Problem Firewalls: Restrict ports Inspect protocol Solution Proxy procedure calls over HTTP

Origins Early 1998 Data marshaled into XML messages All request and responses are human-readable XML Explicit typing Transport over HTTP protocol Solves firewall issues No true IDL compiler support (yet) Lots of support libraries

XML-RPC example <methodCall> <methodName> sample.sumAndDifference </methodName> <params> <param><value><int> 5 </int></value></param> <param><value><int> 3 </int></value></param> </params> </methodCall>

XML-RPC data types int string boolean double dateTime.iso8601 base64 array struct

Assessment Simple (spec about 7 pages) Humble goals Good language support Little/no function call transparency Little/no industry support Mostly grassroots

SOAP origins ( Simple ) Object Access Protocol 1998 and evolving (v1.2 Jan 2003) Microsoft & IBM support Specifies XML format for messaging Not necessarily RPC Continues where XML-RPC left off: XML-RPC is a 1998 simplified subset of SOAP user defined data types ability to specify the recipient message specific processing control and more … XML (usually) over HTTP

Web Services and WSDL Web Services Description Language Analogous to an IDL Describe an organization’s web services Businesses will exchange WSDL documents

WSDL Structure <definitions> <types> data type used by web service: defined via XML Schema syntax </types> <message> describes data elements of operations: parameters </message> <portType> describes service: operations, and messages involved </portType> <binding> defines message format & protocol details for each port </binding> </definitions>

WSDL structure: port types <definitions name="MobilePhoneService“ target=…> <portType name="MobilePhoneService_port"> <operation name="getListOfModels"> <operation name="getPrice"> <Input message="PhoneModel"/> <output message="PhoneModelPrice"/> <output message="ListOfPhoneModels"/> 2. service definition 1. type definitions 3. messaging spec

WSDL part 3: messaging spec <binding name="MobilePhoneService_Binding“ type="MobilePhoneService_port"> <soap:binding style="rpc“ transport="http://schemas.xmlsoap.org/soap/http“ /> <operation name=" getPrice "> <soap:operation soapAction=" urn:MobilePhoneService "/> <input> <soap:body encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/“ namespace="urn:MobilePhoneService" use="encoded"/> </input> <output> <soap:body encodingStyle= "http://schemas.xmlsoap.org/soap/encoding/“ namespace="urn:MobilePhoneService" use="encoded" /> </output> </operation> </binding>

Problems with COM/DCOM Originally designed for object linking and embedding Relatively low-level implementation Objects had to provide reference counting explicitly Languages & libraries provided varying levels of support A lot for VB, less for C++

Microsoft .NET Microsoft’s Internet strategy Not an OS Delivers software as web services Framework for universally accessible services Server-centric computing model

Components New object runtime environment Prefabricated web functionality Web services Windows Forms Visual Studio .NET Make it easy to program .NET-compliant programs and build web services

New object runtime environment Common Language Runtime (CLR) Services compile to Intermediate Language ( IL ) Language neutral C++, C#, VB, Jscript + 3 rd party support Common class libraries ADO.NET, ASP.NET, Windows Forms

Common Language Runtime Implementation of common features: lifetime management garbage collection security versioning When first loaded (prior to running): CLR runs just-in-time compiler to generate native code Never interpreted

.NET Remoting Object interaction across application domains Invoke remote objects Object derived from MarshalByRefObject Proxy created when object is activated CLR intercepts calls The CLR is told which classes are remote so it can do the right thing when the client requests a new object Passing objects as parameters Objects implement ISerializable interface

.NET Remoting Communication over channels HTTP channel - XML/SOAP encoding TCP channel - binary encoding SMTP – XML/SOAP encoding

Object Lifetime Single Call : new instance per call (stateless) Singleton : same instance for all requests Client Activated Objects: Similar to DCOM (COM+) Each time a method is called: Lease time set to max of current LeaseTime and RenewOnCallTime Requestor has to renew lease when LeaseTime elapses No more reference counting!

Web functionality ASP.NET Evolution of existing ASP product New smart controls in web pages .NET Web Services Function-based way to expose software functionality to clients

.NET Web Services Based on: HTTP – communications protocol HyperText Transfer Protocol XML – data format eXtended Markup Language SOAP – format for requesting services Simple Object Access Protocol WSDL – format for defining services Web Services Definition Language UDDI – protocol for discovering services Universal Description, Discovery, & Integration

.NET Web Services vs. SOAP SOAP is lower-level messaging protocol Web Services provides higher level of abstraction Write .NET object as if it were accessed by local clients Mark it with attribute that it should be available to Web clients ASP.NET does the rest Hooks up an infrastructure that accepts HTTP requests and maps them to object calls Service description in WSDL Automatically generated by examining metadata in .NET object

Web Service invocation ASP.NET HTTP request Method/parameters Encoded in XML Process ASP Unmarshal msg Invoke procedure .NET object Method 1 Method n Web Server

Web Service invocation ASP.NET HTTP request Method/parameters Encoded in XML Process ASP Unmarshal msg Return data Marshal return data Encoded response .NET object Method 1 Method n Web Server

Away from RPC… More Web Services

Until 2006… Google Web APIs Developer Kit - SOAP www.google.com/apis/download.html A WSDL file you can use with any development platform that supports web services. A Java library that provides a wrapper around the Google Web APIs SOAP interface. An example .NET program which invokes the Google Web APIs service. Documentation that describes the SOAP API and the Java library.

The future of SOAP? SOAP Dropped by Google in 2006 Alternatives exist: AJAX, XML-RPC, REST, … Allegedly complex because “we want our tools to read it, not people” – unnamed Microsoft employee Microsoft SOAP APIs for Microsoft Live http://search.live.com/developer

AJAX A synchronous J avaScript A nd X ML Asynchronous Client not blocked while waiting for result JavaScript Request can be invoked from JavaScript (using HTTPRequest) JavaScript may also modify the Document Object Model (CSS) – how the page looks XML Data sent & received as XML

AJAX & XMLHTTP Allow Javascript to make HTTP requests and process results (change page without refresh) IE: new ActiveXObject(“msxml3.XMLHTTP”) Mozilla/Opera/Safari: new XMLHttpRequest() xmlhttp.open(“HEAD”, “index.html”, true) Tell object: Type of request you’re making URL to request Function to call when request is made Info to send along in body of request

AJAX on the Web Google Maps, Amazon Zuggest, Del.icio.us Director, Writely, … Microsoft ASP.NET AJAX 1.0 January 2007 Integrate client script libraries with ASP.NET server-based code Google recommends use of their AJAX Search API instead of SOAP Search API

REST RE presentational S tate T ransfer Stay with the principles of the web Four HTTP commands let you operate on data (a resource): PUT (insert) GET (select) POST (update) DELETE (delete) In contrast to invoking operations on an activity. Message includes representation of data.

Resource-oriented services Blog example Get a snapshot of a user’s blogroll: HTTP GET //rpc.bloglines.com/listsubs HTTP authentication handles user identification TO get info about a specific subscription: HTTP GET http://rpc.bloglines.com/getitems?s={subid} Makes sense for resource-oriented services Bloglines, Amazon, flikr, del.icio.us, …

Resource-oriented services Get parts info HTTP GET //www.parts-depot.com/parts Returns a document containing a list of parts (implementation transparent to clients) <?xml version="1.0"?> <p:Parts xmlns:p="http://www.parts-depot.com" xmlns:xlink="http://www.w3.org/1999/xlink"> <Part id="00345" xlink:href="http://www.parts-depot.com/parts/00345"/> <Part id="00346" xlink:href="http://www.parts-depot.com/parts/00346"/> <Part id="00347" xlink:href="http://www.parts-depot.com/parts/00347"/> <Part id="00348" xlink:href="http://www.parts-depot.com/parts/00348"/> </p:Parts>

Resource-oriented services Get detailed parts info: HTTP GET //www.parts-depot.com/parts/00345 Returns a document containing a list of parts (implementation transparent to clients) ?xml version="1.0"?> <p:Part xmlns:p="http://www.parts-depot.com" xmlns:xlink="http://www.w3.org/1999/xlink"> <Part-ID>00345</Part-ID> <Name>Widget-A</Name> <Description>This part is used within the frap assembly</Description> <Specification xlink:href="http://www.parts-depot.com/parts/00345/specification"/> <UnitCost currency="USD">0.10</UnitCost> <Quantity>10</Quantity> </p:Part>

REST vs. RPC Example from wikipedia: RPC getUser(), addUser(), removeUser(), updateUser(), getLocation(), AddLocation(), removeLocation() exampleObject = new ExampleApp(“example.com:1234”); exampleObject.getUser(); REST http://example.com/users http://example.com/users/{user} http://example.com/locations userResource = new Resource(“http://example.com/users/001”); userResource.get();

REST-based Systems Yahoo! Search APIs Ruby on Rails 1.2 Open Zing Services – Sirius radio svc://Radio/ChannelList svc://Radio/ChannelInfo?sid=001-siriushits1&ts=2007091103205

ONC RPC, DCE RPC/DCE Language/OS independent (mostly UNIX, some Windows) No polymorphism No dynamic invocation DCE RPC added: UUID layer of abstraction: a cell of machines

Microsoft DCOM/ORPC ORPC : slight extension of DCE RPC Single server with dynamic loading of objects (surrogate process) Platform dependent – generally a Microsoft-only solution Support for distributed garbage collection Clients pings server to keep references valid

Java RMI Language dependent (Java only) Architecture dependent (JVM) Generalized (and programmable) support for object serialization No dynamic invocation No support for dynamic object/interface discovery

CORBA Cross-platform: language/OS independent Widespread support Support for object-oriented languages Dynamic discovery and invocation Object life-cycle management Persistence Transactions Metering Load balancing Starting services

XML-RPC/SOAP/.NET XML over HTTP transport Relatively easy to support even if language does not have a compiler (or precompiler) WSDL – service description Proxy over HTTP/port 80 Bypass firewalls SOAP has gotten bloated; large messages .NET Remoting & Web Services introduces Language support for deploying web services (you don’t have to deal with SOAP) Library support, including predefined services

AJAX, REST AJAX Designed for web client-server interaction Simple JavaScript calling structure using XMLHTTPRequest class You can encapsulate SOAP requests or whatever… REST Sticks to basic principles of HTTP. Posits that you don’t need additional communication streams or the method-like abstractons of SOAP or RMI

Rpc Case Studies (Distributed computing)

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