Messages are sent over the message bus. For optimal performance, messages may be sent over dedicated queues and topics. This page describes a suggested use of queues and topics.
The destinations are split into different categories, inspired by Java JMS. There are four types of possible JMS destinations:
The following sections documents the destinations used in the reference architecture together with alternatives. Note all destinations in the reference architecture are local to a given repository.
LISTENERS: Every component participating in a Bit Repository.
DISCUSSION: This topic is the abstraction layer, that makes it possible to use the protocol with no knowledge of other participants. The destination is used to send the initial 'Identify...' requests used to start a conversation. See Message flow documentation for details.
IMPLEMENTATION: The topic is defined in the RepositorySettings.
LISTENERS: One specific pillar
DISCUSSION: This topic is the interface for requesting operations on a pillar.
IMPLEMENTATION: Pillar topics are identified through the IdentifyPillarFor<Op>Responses returned as a result of a IdentifyPillarFor<Op>Request.
GENERATION: These topics are generated for each pillar by the message bus administrator when a new repository is setup.
ALTERNATIVES: It is protocol-safe to make a different choice for making pillar destinations on a per-pillar basis. This can be replaced with a queue or a temporary queue, and the naming is quite optional. A topic seems appropriate, since it will not have persistent messages lying around if the pillar is not available at the time of request. However, there could also be advantages of a queue, since you could replicate you pillar instances and only one would receive the message. It may be considered desirable to use temporary queues, so the queue name will never be reused in a later operation.
MESSAGE: IdentifyPillarFor<Op>Response, <Op>Response, <Op>Complete
DISCUSSION: This queue is intended to receive replies to requests sent to the clients. The reference maintains a conversation state while running, which isen't shared between client, nor persisted. This means replies sent to other clients or previous instances of a client are irrelevant. Thus a client is only interested in replies to it's own responses.
IMPLEMENTATION: A client initiates a temporary queue on startup with a unique identifier.
ALTERNATIVES: It is protocol-safe to make a different choice for making client destinations on a per-client basis. This can be replaced with a queue or a (durable shared) topic, and the naming is quite optional. In case of stateless client, clients with persisted state or shared state this might be relevant.
Alarms are probably best modelled in a separate destination.
LISTENERS: One specific client
DISCUSSION: This queue is intended to receive alarms that are reported during a SLA-specific conversation.
IMPLEMENTATION: All participants in the protocol are given the alarm destination id in it's configuration, and send alarms to this topic.
ALTERNATIVES: The repository topic could be used instead.