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Topics are used for initiating operations (Operations ending in ...Request). This seems appropriate for initiating an operation. Topic semantics are required for the Identify...Request operations. Followup messages MAY be sent to a topic, but in this case replies are not persistent, so queues are suggested.
The
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Collection topic
LISTENERS: Every client or pillar recognising this SLAcomponent participating in a Collection.
MESSAGES: IdentifyPillarFor<Op>Request, other messages MAY be sent on this topic.
NAMING: "<slatype:<collection-id>"
DISCUSSION: This topic is the abstraction layer, that makes it possible to use the protocol with no knowledge of other playersparticipants.
IMPLEMENTATION: A participant in the protocol is given a list of all SLA's it should recognise in configuration, and all listeners connect to this topicThe topic is defined in the Collection settings.
GENERATION: This topic is generated by the message bus administrator when a new SLA Collection is addedsetup.
The per-pillar topic (note: See "ALTERNATIVES" for other choices than a topic)
LISTENERS: One specific pillar
MESSAGES: <Op>Request
NAMING: "<slatype:<collection-id>.<pillar-id>"
DISCUSSION: This topic is the interface for requesting operations on a pillar.
IMPLEMENTATION: A pillar in the protocol is given it's id in configuration, and for each SLA listeners connect to this topicPillar 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 SLA Collection is addedsetup.
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.
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The dedicated client durable topic
LISTENERS: One specific clientClients
MESSAGE: IdentifyPillarFor<Op>Response, <Op>Response, <Op>Complete
NAMING: "<slatype:<collection-id>.client"
DISCUSSION: This durable topic is intended to receive replies to requests sent to the clients.
IMPLEMENTATION: A client in the protocol is given the SLA id in it's configuration, and each listener connects to this durable topic.
GENERATION: This durable topic is generated for each SLA by the message bus administrator when a new SLA is added.
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 temporary queue, and the naming is quite optional. A persistent destination seems appropriate, since it will ensure that replies are received and processed, even if the listener is not available when the message was sent. However, it may be considered desirable to use temporary queues, so the queue name will never be reused in a later operation.
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Alarms are probably best modelled in a separate destinations. Currently it is expected that two destinations for alarms are reasonable:
The general alarm durable topic
LISTENERS: An alarm service
MESSAGE: Alarms
NAMING: "ALARMS"
DISCUSSION: This topic is intended to receive alarms that are general for the system.
IMPLEMENTATION: All participants in the protocol are given the topic name ("ALARMS") in configuration, and send general alarms to this topic. The ALARM service also listens to this topic.
GENERATION: This topic is generated by the message bus administrator when first setting up the system.
ALTERNATIVES: The GENERAL topic could be used instead, or all known SLA topic destinations.
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destination.
The Collection alarm durable topic
LISTENERS: One specific client
MESSAGE: Alarms
NAMING: "<slatype:<collection-id>.alarms"
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 SLA id in it's configuration, and send SLA-specific alarms to this topic.
GENERATION: This durable topic is generated for each SLA by the message bus administrator when a new SLA is added.
ALTERNATIVES: The SLA topic could be used instead.
Other proposed destinations
The General Topic
LISTENERS: Everybody.
MESSAGES: None defined, but all can be sent to this topic
NAMING: "GENERAL"
DISCUSSION: This topic is a fallback, if for any reason the proper communication channels are not available. Currently, we try to do without it, since it seems a dangerous practice to communicate on a shared channel that everybody listens to.
IMPLEMENTATION: A participant in the protocol is given the topic name ("GENERAL") in configuration, and all listeners connect to this topic.
GENERATION: This topic is generated by the message bus administrator when first setting up the system.