I need to create a system that uses the Publish / Subscribe bus (for example, Mule, ZeroMQ, RabbitMQ), but in the literature everyone implies that subscriber applications are reliably available to receive messages from those to which they subscribe as soon as the Pub / Sub bus can deliver a message.
I have a system in which some of the applications will be securely connected to the Publish / Subscribe bus, but other applications will not be active or connected to the bus all the time.
The obvious solution is to have some kind of “present” protocol between the untrusted application and the Publish / Subscribe bus, so that the “real” applications deliver their messages immediately and the “no” applications have their messages in the queue, a constant buffer of some type, and as soon as they complete the "handshake of presence", messages in the queue are delivered to the new application.
Are there any publish / subscribe journals that have a built-in feature in them, or are there any open source extensions that do this? Can you point me to any urls that describe this?
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