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SOAP Events Aleksander Slominski IU Extreme! Lab An Extensible and Interoperable Event System Using SOAP (xEvents Reference Implementation)

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Presentation on theme: "SOAP Events Aleksander Slominski IU Extreme! Lab An Extensible and Interoperable Event System Using SOAP (xEvents Reference Implementation)"— Presentation transcript:

1 SOAP Events Aleksander Slominski IU Extreme! Lab An Extensible and Interoperable Event System Using SOAP (xEvents Reference Implementation)

2 Outline Scope and Requirements Whirlwind survey of existing standards Event System Design SOAP Events Core (Base Event Type, Event Listener) Advanced (Passing Remote References, Leasing Event Channels) Implementation: xEvents on top of SoapRMI 1.1 Java / C++ Further work

3 Scope Application and Component Level Events Not real time or multimedia Focus on events that glue disparate components and allows for easy application integration (as painless as possible…) Optimal solution: simple (good for majority of cases) but extensible (for the rest) and easy to deploy (leveraging existing standards)

4 What is Event? time stamped message delivered from source to subscribed listeners that contains typed data may contain sequence number to prevent duplication and time-to-live

5 Requirements Simple Make typical cases simple Extensible Make other cases possible Easily Deployable Uses standards Language and Platform Independent Internet Friendly (firewalls…)

6 Requirements - details Naming How to find event publishers (LDAP, …) Types - Extensible Data Format Today it means XML and XML schemas… Internet Enabled Works with HTTP (firewalls, NAT, …) Can survive and recover from failures … Simple OO Extensible Interfaces (IDL, …) Security – Leveraging Existing Standards TLS/SSL, X.509 certificates, digital signatures, …

7 Tour of Existing Standards Corba Events Jini Events Over 100 other event systems (or more) Ad hoc solutions – application specific mechanism using proprietary format write to file, socket, and other magic …

8 Corba Events Naming Service to locate listeners Push/Pull models and good performance Available solutions to enable Internet computing through firewalls (but not designed for) and can have load balancing and failure recovering mechanisms Use of IDL to describe interfaces Available extensions for security High Performance and Multiple Languages but Complex and Steep Learning Curve …

9 Jini Events Naming with Jini Lookup Service (some limitations but can use optionally JNDI) Event is Java Object (good extensibility) Listener interface - flexible publisher model Leasing - very good for self healing Uses RMI (available solutions for firewalls) Leverages Java for security Easy to use but limited to Java (generally)

10 Ad Hoc Solutions It works! (for given application) but: it does not works with others (on Grid) … Can be very well optimized and probably is well contained (no need to change it!) Existing applications are typically hard to modify therefore simple interoperable event mechanism is crucial (in FORTRAN/C just function call to library etc.) Typically limited to the application and hard to connect to other event systems

11 Conclusions Any proposed event mechanism must work with existing event standards No one solution is good for everything … Therefore it is important to have simple and extensible event system that can easily be added to existing applications It must allow for easy naming, object types, security and leverage Internet standards

12 Event System Design Choices made for this event system

13 Design objectives Events are signals (small size) and actual data transfers should use more high performance messaging protocols Platform and language independent Pervasive and simple format - XML Easy to receive, use (parse) and store Works and adapts to Internet using most widespread global protocol – HTTP Naming (LDAP) and Security (SSL/X.509)

14 SOAP 1.1 Standard supported by both IBM and Microsoft (foundation of.NET strategy) Elegant and simple Builds on top of XML and XML Schemas XML it is verbose but good to create common data format and easy to transform XML Schemas to describe what we actually send and expect to receive (object types)

15 Naming Leverage existing and working standard Minimum: support LDAP Allow to work with emerging standards such as UDDI to describe event services SOAP can be easily extended to allow to store remote references in naming services

16 Types Extensible but simple system to describe event types Not centralized and platform independent Easy to store, process and query XML and XML schemas fits the bill

17 Internet Enabled SOAP RPC = HTTP + XML Simple but extensible RPC model Defines HTTP bindings for SOAP Robust and easy to implement Good to send signals and also to provide tle lowest common denominator protocol ex. to negotiate compression, encryption, QoS or type of faster binary protocol used Firewall friendly (leverages HTTP infrastructure)

18 WAN & distributed computing Everything can fail just any time.. Therefore it is important to incorporate leasing concept However if necessary allow for unleased operations (when leasing can not work with existing applications or components)

19 Simple OO Interfaces Event interfaces should not hide but expose objects Easy to understand and to extend WSDL or IDL to describe what is event listener and how to subscribe with publisher Promote interoperability Must be language and platform independent

20 Security Rarely can be added later SOAP already can use HTTP level security (TLS/SSL) Proposed extension to SOAP to support digital signatures Event system should allow to operate in unsafe mode (for testing, debugging, …)

21 SOAP Events Core Translating requirements into event system architecture …

22 Event Design Builds on top of SOAP 1.1 encoding eventType and source can be used for filtering and message dispatching seqNum prevents against delivering duplicated events message contains descriptive information timestamp – time in milliseconds since UNIX epoch

23 SOAP Event Event is a base class and it contains following fields: eventNamespace – URI of namespace eventType – dot hierarchical event type name source – string describing source (depends on eventType) timestamp – in milliseconds since UNIX epoch seqNo – sequence number message – human readable description of the event handback – described later with subscription Event type is defined by XML schema: (next slide)


25 Example: Resource Event http://www.extreme.indiana.ed u/soap/events/resdat#MachineUtilizationEvent resdata.machine.utilization 982862312897 0.88 123988


27 Event Listener Very simple interface Only one method that accepts Event Can throw SOAP 1.1 Fault in case of exceptions In Java pseudo code (WSDL etc. in future): interface EventListener { void handleEvent(Event ev) throws Exception; }

28 SOAP Events and others Interoperability Any SOAP compliant implementation may publish and listen for events and use Event Channel Mobility To generate events there is no need to have full fledged SOAP – it is enough to write pre-formatted strings into socket.

29 Do We Need More? Actually core SOAP Events has all that is necessary to publish and listen for events! However it would be nice to have more: Using and storing simple remote references (in file or in Naming Service) Lease and leasing event publishers Event channels to decouple event publisher and listeners

30 SOAP Events Channels Decoupling producers from consumers (Event Channels) Supporting leased subscription (and simple XML Remote Reference) to deal with inherent distributed system failures Using Naming Service for higher reliability: mobile event listeners and channels supports dynamic failure recovery (lease renew + lookup)

31 Simple Remote Reference Location of remote endpoint (web service) What is the type of endpoint (uniquely identified by URI to its IDL) That is it! However sometimes it is necessary to have: URI namespace of of the endpoint (required by Apache SOAP) SOAPAction

32 Example of Remote Reference v11:leasing-filtered-event-channel urn:soaprmi-v11:leasing- filtered-event-channel urn:soaprmi-v11:temp-java-port-type el

33 Port = Remote Reference Port has Endpoint(s) Endpoint has Location (URL) Endpoint may have optionally Binding Binding may contain endpoint dependent parameters (in example it is name that describes SOAP URI) Port type is uniquely identified by pair (uri, name) and it may point simply to WSDL (ex. http://host/myService.wsdl#Listener) This is just XML and can be stored in Directory Service

34 Leased Event Subscription Subscribe passing remote ref and asking for lease (EventListener is Port) When subscribing an event lease is returned (simple object that contain duration of lease granted) interface LeasingFilteredEventPublisher { EventLease subscribeLease( EventListener listener, Event filter, long leaseDuration, String handback) throws Exception; }

35 Yet another XML schema …

36 Example Subscribe Request It is using SOAP-RPC HTTP header SOAP envelope and body and XML element with function name (subscribeLease) and namespace identifying endpoint (from binding) Parameters First parameter is remote reference (it is Port) The rest of parameters End of SOAP envelope

37 HTTP Headers POST /leasing-filtered-event-channel HTTP/1.0 Host: localhost Content-Type: text/xml Content-Length: 1475 SOAPAction: "http://localhost:4566/leasing- filtered-event-channel#subscribeLease" Connection: Close …

38 SOAP Envelope and Call

39 First param with remote-ref urn:soaprmi-v11:simple-listener v11:simple-listener urn:soaprmi-v11:simple-listener urn:soaprmi-v11:temp-java-port-type

40 Rest of parameters and closing of SOAP envelope … 240000

41 Event Channels Event Channel = combination of Even Listener with Event Publisher: public interface EventChannel extends EventListener, EventPublisher { } public interface LeasingFilteredEventChannel extends EventChannel, LeasingFilteredEventPublisher { }

42 Implementation: xEvents xEvents is implemented in SoapRMI C++ and Java (also can be used from Jython) This is proof-of-concept implementation To check that SOAP Events design will work with any SOAP 1.1 compliant implementation.

43 SoapRMI Design Motivation RMI model Web services Distributed Events

44 Typical RMI Scenario Registry [Java/C++/…] Client [Java/C++/…] Server [Java/C++/…] SOAP on the wire 2.1. 3. Internet space http://host:8888/server …

45 Stages in RMI scenario 1. Server publishes remote reference: Server serverImpl = new ServerImpl(); Naming.bind(“helloService”, serverImpl); 2. Client lookups server remote reference: Server serverRef = (Server) Naming.lookup(“helloService”); 3. Client execute call on server: serverRef.sayHello(“World”);

46 Web Services http://host:8888/ser ver … Client [Java/C++/…] Server [Java/C++/…] Load service description (SOAP/Files/WebDAV) Publish service description (SOAP/Files/WebDAV) Service Directory SOAP on wire http://host:8888/ser ver …

47 Distributed Events http://host:8888/ser ver … Listener [Java/C++/…] Publisher [Java/C++/…] http://host:8888/se rver … Load service description (SOAP/Files/WebDAV) Publish service description (SOAP/Files/WebDAV) Subscription SOAP on wire

48 SOAP Events Events Publisher Events Listener Implemented as: Java application C/C++ application Python script Others: Perl, VB, … SOAP handleEvent SOAP handleEventResponse Implemented as: Java application Servlet Python script Others: Perl, VB, … SOAP 1.1

49 SOAP and SoapRMI RMI system on top of SOAP (simple API) Supports Web Services SoapRMI remote object can be put into servlet To contact specify URL and interfaces Naming services Standard RMI registry (Naming.bind, …) JNDI for Java (and access OpenLDAP) SoapRMI Registry-to-JNDI bridge for C++

50 Implementation Details Compliant with SOAP 1.1 Sample code available to show how to write event publishers and listeners in SoapRMI Java and C++ Extensibility Events are objects and can be extended XML Schema can be used to describe event format and we have support for mapping schema types into objects

51 xEvents Publisher Open socket, write string, close socket (or keep open for keep-alive) Listener Accept socket, parse simple XML, do stuff Event channel with filtering (and persistence) Easily pluggable: Event Listener or Event Channel can work standalone or in Servlet

52 EventListener Very simple interface (throws RemoteException that maps to SOAP Fault): interface EventListener { void handleEvent(Event ev) throws soaprmi.RemoteException; }

53 EventPublisher Each event publisher may have its own API EventPublisher is just simple marker interface interface EventPublisher { }

54 LeasingFilteredEventPublisher We provide one simple push subscribe with lease: public interface LeasingFilteredEventPublisher extends EventPublisher { EventLease subscribeLease(EventListener myReference, long leaseDuration, Event filter, String handback ) throws RemoteException; }

55 EventChannel Event channel decouples event publishers and listeners and it is both publisher and listener: public interface EventChannel extends EventListener, EventPublisher { } public interface LeasingFilteredEventChannel extends LeasingEventChannel, LeasingFilteredEventPublisher { }

56 Implementation Most of xEvents are interfaces and few basic classes such as Event However in package is simple implementation of Listener (standalone and as servlet) Publisher (produces machine utilization events) Leasing Filtered Event Channel

57 Performance On the order of 100 round-trip events/sec though raw XML parsing speed of 5000/sec Can be fine tuned for particular event types or implemented in C++ To receive events parsing can be done by hand if received event types are limited or using simple and small XML Pull Parser both for C++ and Java Persistent event channel uses JDBC and MySQL for backend

58 XML Parsing Available strategies DOM: put parsed tree in memory and allow to manipulate it SAX: pick what you need from input stream XPP (XML Pull Parser): parse incoming stream Mixed: progressive DOM – combining SAX with creating DOM on demand Layers: XPP -> SAX -> DOM For events: low CPU and memory overhead

59 XML Pull Parser Designed to unmarshal complex data structures from XML (such as SOAP) Can be easily embedded in any application Minimized memory allocation during parsing and parser can be reused Tokenizing done in fast automata It is small (20KB for Java JAR file) Used both in SoapRMI Java and C++

60 Example: Resource Monitoring Publisher: Sensor collects data packs it into string and writes into socket connected to EC Small specialized C program without XML parser! Event Channel (EC) receives event parses it and delivers to subscribers SoapRMI Java service: standalone or embedded in servlet Listener: subscribes to EC to receive resource utilization events Java application or servlet that uses SoapRMI

61 SOAP RPC CALL handleEvent HTTP over TCP SOAP Event Publisher Format SOAP Envelope From Template SOAP Events Listener Event Source Event Instance Setting up Publisher - Listener Simple things should be easy to do, such as: connecting producers to consumers: run listener 2001 run publisher http://localhost:2001 Listener and Publisher can be in SoapRMI (C++ or Java) or event hand written.

62 Publishers/Sensors Consumers Channels Java Simple Publisher Java Resdat Sensor1 C++ Resdat Sensor FC: Java Filtering Channel SL: Java Simple Listener RC: Java Resdat Channel TC: Java Test Channel CSL: C++ Simple Listener SL1: Java Simple Listener1 Java Resdat Sensor2 SL2: Java Simple Listener2 resdat.* test.* Producers Listeners

63 Example Setup: Listeners Setup event channels run channel –rebind FC run unfiltered –rebind TC –subscribe FC run unfiltered –rebind RC [NOTE: no –subscribe FC] Setup event listeners run listener –rebind SL –subscribe TC run listener –rebind SL1 –subscribe RC run listener –rebind SL2 [NOTE: no –subscribe RC] Setup dynamic connections: run connect –publisher FC –listener RC run connect –publisher RC –listener SL2

64 Example Setup:Publishers Publishers – start pumping events run publisher TC run sensor FC run sensor RC C++ publisher./sensor FC C++ listener./listener –bind FC

65 Fault Tolerance taking down any part of interconnected event network will not bring down system event listeners (including event channels) are location independent – they rebind their reference on startup and during subscription renewal listeners get updated remote references migration of listeners to another host is supported – publishers will lookup in directory new reference and use it Example: kill FC or SL1 and move to another host

66 How it works? public static void main(String[] args) { parseArgs(args); EventListener listener = Util.getListenerRef(optListener, optCtxUrl); Util.startSubscription(optPublisher, listener, optCtxUrl, 4 * 60 * 1000, …); }

67 How it works (2)? public static LeasingEventChannel getLECRef(String loc, String ctx) throws soaprmi.RemoteException { Remote ref = soaprmi.util.Util.lookupRemote( loc, null, ctx, LeasingEventChannel.class); if(! (ref instanceof LeasingEventChannel)) { throw new RemoteException("remote object is not" +" LeasingEventChannel at location "+loc +" (context "+ctx+")"); } return (LeasingEventChannel) ref; }

68 How it works (3)? public static Remote lookupRemote(String loc, Remote ref, String ctx, Class iface ) throws RemoteException { if(loc.startsWith("http://") || loc.startsWith("https://")) { return soaprmi.soaprpc.SoapServices.getDefault().createStartpoint(loc, new Class[]{iface}); } // do RMI registry lookup String rmi = makeRMIRef(loc, ctx); if(rmi != null) { return Naming.lookup(rmi); }... DirContext dirCtx = getInitialDirContext(ctx); return (Remote) dirCtx.lookup(loc); }

69 Further Work Exploring C++ and Java performance of xEvents Interfacing with other SOAP implementation (currently works with Apache SOAP and preliminary with.NET) Using TLS/SSL transport and leveraging SOAP Digital Signature Extension (SOAP DSig Spec) Integrating xEvents into CCAT and Active Notebook (already working with previous incarnation) Adding Persistent Event Channel

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