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SOAP Events

SOAP Events. An Extensible and Interoperable Event System Using SOAP (xEvents Reference Implementation). Aleksander Slominski IU Extreme! Lab . Outline. Scope and Requirements Whirlwind survey of existing standards Event System Design SOAP Events Core (Base Event Type, Event Listener)

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SOAP Events

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

  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) • http://www.cs.caltech.edu/~adam/isen/event-systems.html • 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)

  24. <schema targetNamespace = “http://www.extreme.indiana.edu/soap/events/” > <element name="Event"> <complexType><sequence> <element name="eventNamespace" type="string"/> <element name="eventType" type="string"/> <element name="source" type="string"/> <element name="timestamp" type="long"/> <element name="seqNo" type="long"/> <element name="message" type="string"/> <element name="handback" type="string"/> </sequence></complexType> </element>

  25. Example: Resource Event <MachineUtilizationEvent> <eventNamespace>http://www.extreme.indiana.edu/soap/events/resdat#MachineUtilizationEvent</eventNamespace> <eventType>resdata.machine.utilization</ev…> <source>rainier.extreme.indiana.edu</source> <timestamp>982862312897<timestamp> <cpuUtilization>0.88< cpuUtilization > <memoryUsed>123988</memoryUsed> </MachineUtilizationEvent >

  26. <schema targetNamespace=“http://www.extreme.indiana.edu/soap/events/resdat/” xmlns:m=“http://www.extreme.indiana.edu/soap/events/” > <import namespace="http://www.extreme.indiana.edu/soap/events/" schemaLocation="event.xsd"/> <element name="MachineUtilizationEvent" base="m:Event" derivedBy="extension"> <complexType><sequence> <element name="cpuUtilization" type="double"/> <element name="memoryUsed" type="long"/> </sequence></complexType> </element> </schema>

  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 <Port> <endpoint> <location>http://192.168.1.7:4566/urn:soaprmi-v11:leasing-filtered-event-channel</location> <binding><name>urn:soaprmi-v11:leasing-filtered-event-channel</name> </binding> </endpoint> <portType> <uri>urn:soaprmi-v11:temp-java-port-type</uri> <name>soaprmi.events.LeasingFilteredEventChannel</name> </portType></Port>

  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 … <schema targetNamespace = “http://www.extreme.indiana.edu/soap/events/” > <element name="EventLease"> <complexType> <sequence> <element name=“duration“ type="long"/> </sequence> </complexType> </element>

  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 <SOAP-ENV:Envelope xmlns:SOAP-ENV='http://schemas.xmlsoap.org/soap/envelope/' xmlns:SOAP-ENC='http://schemas.xmlsoap.org/soap/encoding/‘ xmlns:xsi='http://www.w3.org/1999/XMLSchema/instance/' xmlns:xsd='http://www.w3.org/1999/XMLSchema/' SOAP-ENV:encodingStyle='http://schemas.xmlsoap.org/soap/encoding/'> <SOAP-ENV:Body> <subscribeLease> …

  39. First param with remote-ref <p1 id='id1' xsi:type='ns1:soaprmi.port.Port' xmlns:ns1='urn:soaprmi-v11:temp-java-xml-type'> <endpoint id='id2' xsi:type='ns2:soaprmi.port.Endpoint' xmlns:ns2='urn:soaprmi-v11:temp-java-xml-type'> <binding id='id3' xsi:type='ns3:soaprmi.port.Binding' xmlns:ns3='urn:soaprmi-v11:temp-java-xml-type'> <name xsi:type='xsd:string'>urn:soaprmi-v11:simple-listener</name> </binding> <location xsi:type='xsd:string'>http://192.168.1.7:4561/urn:soaprmi-v11:simple-listener</location> </endpoint> <name xsi:type='xsd:string'>urn:soaprmi-v11:simple-listener</name> <portType id='id4' xsi:type='ns2:soaprmi.port.PortType' xmlns:ns2='urn:soaprmi-v11:temp-java-xml-type'> <name xsi:type='xsd:string'>soaprmi.events.EventListener</name> <uri xsi:type='xsd:string'>urn:soaprmi-v11:temp-java-port-type</uri> </portType> <userName xsi:type='xsd:string'></userName> </p1>

  40. Rest of parameters and closing of SOAP envelope … <p2 xsi:type='xsd:long'>240000</p2> <p3 xsi:type='ns1:soaprmi.events.Event' xmlns:ns1='urn:soaprmi-v11:temp-java-xml -type' xsi:null='1'/> <p4 xsi:type='ns1:string' xmlns:ns1='http://www.w3.org/1999/XMLSchema/' xsi:null ='1'/> </subscribeLease> </SOAP-ENV:Body> </SOAP-ENV:Envelope>

  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++/…] 2. 1. 3. <Port> <location> http://host:8888/server </location> <binding>… </Port> SOAP on the wire Internet space

  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 <Port> <location> http://host:8888/server </location> <binding>… </Port> Server [Java/C++/…] HelloServlet.java Client [Java/C++/…] HelloClient.java SOAP on wire Load service description (SOAP/Files/WebDAV) Publish service description (SOAP/Files/WebDAV) <Port> <location> http://host:8888/server </location> <binding>… </Port> Service Directory

  47. Distributed Events <Port> <location> http://host:8888/server </location> <binding>… </Port> Publisher [Java/C++/…] Listener [Java/C++/…] SOAP on wire Publish service description (SOAP/Files/WebDAV) Load service description (SOAP/Files/WebDAV) <Port> <location> http://host:8888/server </location> <binding>… </Port> Subscription

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

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