Difference between revisions of "DIS-Broker"

Latest revision as of 18:59, 6 July 2016

Introduction

This DIS-Broker is a WSRF service that adopts the singleton pattern. It provides subscription-brokering capability allowing to a client (i.e. the client part of a service) to subscribe to a topic without knowing the location of the notification producer (the Endpoint Reference identifying it). Moreover, the DIS-Broker service supports the subscription to a topic that the producer has not yet exposed. In this case, it maintains the pending subscription until the notification producer registers its topic. The implementation of this service is not based on the brokered notification schema since the DIS-Broker subscribes the consumer directly to the notification producer. In that way there is not a central service that is in charge to receive notifications from producers and to deliver them to the right client (as in the brokered notification architecture). However, the DIS-Broker continues its mediation even after the brokerage of the subscription. In fact, the DIS-Broker automatically manages the relocation of notification producers by forwarding the client subscription requests to the new instances of the producers. This service implementation supports the transparent subscription/re-subscription of the client to the new producer instances that comes up after the initial request of subscription.

Implementation Details

The DIS-Broker Service exposes a set of operations for topic registration/unregistration and for subscription/unsubscription. Even if these methods can be directly accessed by calling the DIS-Broker service, it is mandatory to use the DIS libraries, i.e. the DIS-IP and the DIS-HLS-Client (the related methods are described in DIS-IP and DIS-HLS-Client sections), to be connected to the VO specific instance of the Service. The operations implemented in the DISBrokerService class are:

registerTopic (RegisterTopicMessage)

This operation allows the DILIGENT services to publish their Topics in the DIS infrastructure. It updates the service status by modifying the collection, named topicMapping HashMap, where the mappings between topics and the producer EPR are stored. In the case of pending subscription requests, this method subscribes consumer to the given EPR. It also automatically registers existing consumers interested in the topics to newly registered producers. The RegisterTopicMessage parameter contains:

• EndpointReferenceType producerERP: the producer EPR that exposes the Topics;
• VectorStub topicVector: a vector of Topics that the producer wants to register.

unregisterTopic(RegisterTopicMessage)

This operation allows the DILIGENT services to un-publish their Topics (or a part of them) from the DIS infrastructure. It updates the service status by modifying the collection, named topicMapping HashMap. If no more services expose the same Topics, it removes the entries referred by the given Topics from the internal collection and it un-subscribes all the related consumers. The parameter is the same described in the RegisterTopic operation.

subscribeToTopic(SubscribeMessage)-> EndpointReferenceType []

This method allows consumers to subscribe to a particular Topic (without knowing the EPR of the producers). The consumer is subscribed to all services that expose the given Topic: then it is up to consumers to filter the inappropriate notification message. A consumer can also subscribe itself to a Topic that has not yet published on the DIS-Broker: in this case, the subscription request remains pending until a service registers the given topic. It will also be subscribed to newly appearing producer, even after a successful subscription. According to the Java WS Core implementation of the WS-Base Notification specification. the producer is in charge to send notifications to consumers. Whilst the DIS-Broker is in charge of dispatching subscription requests to the appropriate producers. The SubscribeMessage parameter contains:

• EndpointReferenceType clientEPR: the consumer EPR;
• String topic: the topic (as a serialized String of the topic QName);

If the DIS-Broker already manages the given topic, the service returns the list of topic notifiers.

listTopic()-> String[]

This method retrieves the list of topics managed by the DIS-Broker Service

listTopicForNotifiers(EPR)-> String[]

This method retrieves the list of topic the given EPR notiifier is managing.

getSubscribersForTopic(Topic) -> EndpointReferenceType []

This method retrieves the list of Subscribers EPRs currently subscribed to the given topic.

removeSubscription(SubscribeMessage)

This method allows consumers to remove the subscription to a particular topic. The service updates its internal status and destroys the Subscription Reference on the consumer side. The parameter is the same described in the SucbrcibeToTopic operation.

Dependencies

The dependencies of the DIS-Broker Service are:

• DILIGENTProvider: to publish WS-Resource Properties in the DIS
• DIS-IP: to publish WS-Resource Properties in the DIS and to register WS-Resource Properties in the DIS.
• DVOS Authentication API
• DVOS Delegation Service
• DVOS Common Library.

Usage Example

The DIS-Broker service can be seen as a registry supporting subscription mediation between notification consumers and producers. The producers publish the Topics on which they want to support notification for changes, and consumers contact the DIS-Broker in order to subscribe to/unsubscribe from a topic. The interaction between consumers/producers and the DIS-Broker is implemented by the DIS libraries, DIS-IP and DIS-HLS-Client. A notification producer to register/un-register topics uses the DIS-IP; while on the other hand, a notification consumer exploits the DIS-HLS-Client capabilities to subscribe/unsubscribe to/from Topics.

Known Bugs and Limitations

The DIS-Broker data structures persistency is not fully implemented and tested and has been removed from the Beta version of this component. The DILIGENT Final release will contain a persistent DIS-Broker.

--Andrea 12:29, 1 June 2007 (EEST)