Subscription Model Overview

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Subscription Model Overview

Decentralized Software Services (DSS) uses a publish-subscribe model to dynamically communicate changes in service state from a publishing service to one or more subscribers. This is facilitated by the subscription manager service, which is one of the DSS system services.

Using a subscription manager enables a service author to delegate responsibility for managing a list of subscribers and subscription lifetimes to a common implementation that behaves the same for all services. The subscription manager also offers additional capabilities including filtering of notifications based on notification type, and filtering based on text keys.

This topic explains how to use a subscription manager both from the perspective of a publishing service and also the perspective of a subscribing service.

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A publishing service handles Decentralized Software Services Protocol (DSSP) Subscribe requests by sending a DSSP Insert message to a subscription manager to add the new subscriber to the list of current subscribers. The response from the subscription manager is then passed back to the subscriber . As part of a Subscribe request, a subscriber may indicate a filter describing the set of event notifications that it is interested in. If no filter is provided then all event notifications are sent to the subscriber.

Following the DSSP event notification model, event notifications are generated as a result of state changes in a service. When the state of a service changes, it sends the state change in the form of a DSSP Submit message to a subscription manager with the updated state. The subscription manager then sends the state change to all subscribers for which the event notification matches the subscription filter.

 

 

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