CODEWITHSUNDEEP
rabbitmqqueuestatemessage
Ivan M
Ivan M

Reputation: 61

RabbitMQ Message States

I'm working with RabbitMQ and I'd like to have multiple consumers doing different things for the same message, with this message being exactly in one queue.Each consumer would work on his own, and in the moment the consumer ends with his part, it marks the message as having completed phase "x" , when all the phases are completed for one message, then use the method a basicAck() to remove our message from the queue.

I suspect this to be impossible, if so, I would face this in other way. Having multiple queues with the same message ( using an exchange), each queue with a different consumer , which would communicate with with a Server. This server would then work with a database and checking/updating the completed phases. When all the phases are completed, log it in some way.

But this workaround seems exceedingly unefficient, I'd like to skip it if posssible.

Could it be posssible to set "states" or "phases" to a message in rabbitMQ?

Upvotes: 0

Views: 1429

Answers (1)

theMayer
theMayer

Reputation: 16177

So, first of all, in the context you're talking about, a "message" is an order to do some unit of work.

The first part of your question, by referring to "marking the message" treats the message as a stateful object. This is incorrect. Once a message is produced, it is immutable, meaning no changes are permitted to it. If you violate, or attempt to violate this principle, you have made an excursion beyond the realm of sound design.

So, let's reframe. In a properly-archtiected message-oriented system, a message can represent either a command ("do something") or an event ("something happened"). Note that sometimes we can call a reply message (something sent in response to a command) a third category, but it's really a sub-category of event.

Thus, we are led to the possibility of having (a) one message going to one queue, to be picked up by one consumer, or (b) one message going to many queues, to be picked up by many consumers. You take (a) and (b) to compose complex system behaviors that evolve over time with the execution of each of these small behaviors, and suddenly you have a complex system.

Messages do, in fact, have state. Their state is "processed" or "unprocessed", as appropriate. That is the limit to their statefulness.

Bottom Line

Your situation describes a series of activities (what each consumer does) being acted upon some sort of shared state among the activities. The role of messages and the message broker is to assist in the orchestration of these activities, by providing instruction on what to do (via commands) and what took place (via events). Messages themselves cannot be the shared state. So, you still need some sort of a database or other means to persist the state of your system. There is no way to avoid this.

Upvotes: 2

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