CODEWITHSUNDEEP
servicebusrebus
Lybecker
Lybecker

Reputation: 628

Pub/sub with durable messages with Rebus

I need a way to publish messages to unknown number of subscribers. The messages should be durable/persisted and categorized into three priorities (high, medium and low). One of the subscribers can only handle a limited load and some messages are just more important. High-prioritized messages processed first etc.

How do I do that with Rebus? I guess I need three queues per subscriber?

Where can I find a publish/subscribe example with durable queues and MSMQ?

Upvotes: 3

Views: 1441

Answers (1)

mookid8000
mookid8000

Reputation: 18628

First, some info: Rebus likes to work with durable queues, durable messaging, and guaranteed delivery. In fact, unless you actively do stuff to opt out, that's the way everything works. So if you manage to make pub/sub work with Rebus, it's durable :)

Publishing by definition works with an "unknown number of subscribers" - at least that's a bus concern, and not an application concern.

In reality, subscribers initiate pub/sub conversation by issuing a SubscriptionMessage (which can be seen as a subscription request), which is then followed by the publisher publishing some number of events (which can be seen as "subscription replies"). The "bus part" of the publisher keeps track of who subscribed to any given event type.

So far, so good.

Regarding priorities, there's no out-of-the-box way to achieve that with Rebus. One way to ensure a maximum latency on certain message types is, as you're suggesting, by making separate endpoints whose input queues will not be clogged by low priority messages.

But there is some stuff around how Rebus is configured that strongly suggests having only one single input queue in each process, so that would probably imply that you should create separate processes that subscribe to those high priority message types.

I know that MSMQ supports some kind of priority on messages, so I guess it could be supported by having MsmqMessageQueue understand certain headers (similar to how express delivery and time-to-be-received are implemented - see here) - pull requests are happily accepted and strongly encouraged :)

Upvotes: 3

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