Publishing when there are no consumers (RabbitMQ)

[cocowalla]

I'm testing MassTransit with RabbitMQ. When I publish a message and there are no subscribers, I never see the message in the RabbitMQ queue - is this by design? Are messages purposely discarded if there are no subscribers?

If so, is there any way to change this behaviour so that messages remain in the queue awaiting subsribers who will later consume them?

[Vinay Manda]

Each of the service bus needs to have its own end point. So your publisher might have an end point named Queue1 and might be publishing a message Message1 which might be intended for Queue2.

Unless you have the Queue2 created on the RabbitMQ you would not see the message in Queue2.

Association of the message to the queue happens automatically based on the definitions, and that's the reason you need not specify the queue name where the messages needs to go.

So if there is no subscriber which associates to the message type or if no particular destination uri was mentioned during publishing, the message would not be visible.

I hope that answers your question, else I will let the masters answer or correct me.

[Dru Sellers]

inline

On Sat, Dec 17, 2011 at 3:16 PM, cocowalla <colin.an...@gmail.com> wrote:

I'm testing MassTransit with RabbitMQ. When I publish a message and there are no subscribers, I never see the message in the RabbitMQ queue - is this by design?

yes, if there are no subscribers - there is no one to publish to. if there is no one to publish to there are no queues for the messages to go anywhere. 

 

Are messages purposely discarded if there are no subscribers?

yes. where else would they go? :)

 

If so, is there any way to change this behaviour so that messages remain in the queue awaiting subsribers who will later consume them?

remain in what queue? :)

 

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[cocowalla]

I see your point :)

Here's the scenario:

A subscriber comes online, queue is created
A producer comes online and publishes a message, which the subscriber receives and processes

The subscribers goes offline

I don't want the producer to care if the subscriber is offline - I want it to send messages as usual, and for the subscriber to pick them up next time it comes online.

Is this possible? I've been able to get this behaviour using EasyNetQ, but haven't been able to figure it out with MassTransit

[Dru Sellers]

This is completely doable. You just want a 'permanent' subscription. These will stay around even if the subscriber goes off line.

If you haven't already read through this: http://docs.masstransit-project.com/en/latest/configuration/sub_config_api.html

-d

-d

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[Henrik Feldt]

How would you configure a permanent consumer w/ an IoC container containing the consumers?

Attribute? Or would I have to go into the config part of the app to specify it there, like the docs show?

Henrik

[Chris Patterson]

If you're registering subscriptions in the .Subscribe(sc => {}) method of the ServiceBusFactory, they are permanent by default.

https://github.com/MassTransit/MassTransit/blob/master/src/MassTransit/Configuration/SubscriptionConfigurators/SubscriptionConfiguratorImpl.cs

Otherwise, you need to just not call the UnsubscriptionAction returned by the Subscribe{Consumer|Instance|Handler|Saga} method on IServiceBus.

[Henrik Feldt]

OK, awesome.

Then, what if I want to make them ephemeral ;)? Is there an attribute for that?

[Dru Sellers]

There is no 'attribute'

[cocowalla]

Hmm, I'd read the docs but didn't see that - I'll try it out, thanks :)

[Dru Sellers]

no problem. there's a lot to read and I am still working on how best to present the material.

-d

On Thu, Dec 22, 2011 at 8:45 AM, cocowalla <colin.an...@gmail.com> wrote:

Hmm, I'd read the docs but didn't see that - I'll try it out, thanks :)

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[Chris Patterson]

If ephemoral means non-permanent, yes: Transient().

[cocowalla]

I've tried this, but I must still be missing something, because regardless of how I configure the bus, any messages the producer sends to RabbitMQ while the consumer is offline seem to disappear.

Here's the bus config from the consumer:

this.bus = ServiceBusFactory.New(sbc =>
{
    sbc.UseRabbitMq();
    sbc.UseRabbitMqRouting();
    sbc.ReceiveFrom("rabbitmq://192.168.1.125/MassTransitPoC");

    sbc.Subscribe(s =>
    {
        s.Consumer<RegistrationMessageConsumer>()
            .Permanent();
    });
});

And here's relevant code from the producer:

Bus.Initialize(sbc =>
{
    sbc.UseRabbitMq();
    sbc.UseRabbitMqRouting();
    sbc.ReceiveFrom("rabbitmq://192.168.1.125/MassTransitPoC");
});

Bus.Instance.Publish(
    new RegisterMessage { Id = Guid.NewGuid() }
);

Any idea where I might be going wrong?

[Dru Sellers]

Does it work when both are running?

-d

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[cocowalla]

Yes, seems to work fine if the consumer and producer are running at the same time

[Mick Delaney]

in the management plugin ui can you find the relevant exchange? 

and if so is the exchange marked as durable?

[cocowalla]

Yes, there are relevant fanout exchanges marked as durable, as well as relevant queues marked as durable. The exchanges and queues remain visible in the RabbitMQ after closing the consumer and producer applications.

[Chris Patterson]

You are using the same input queue for each bus, which is a no-no. You need to have a separate queue for the ReceiveFrom for each application.

On Fri, Dec 23, 2011 at 10:46 AM, cocowalla <colin.an...@gmail.com> wrote:

Yes, there are relevant fanout exchanges marked as durable, as well as relevant queues marked as durable. The exchanges and queues remain visible in the RabbitMQ after closing the consumer and producer applications.

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[cocowalla]

Seems I still have a lot to learn about MassTransit!

Should each producer and consumer have a seperate queue? (for example, stick a GUID at the end of the queue name for each producer and consumer instance?

[Dru Sellers]

Yes, each producer and consumer should have its own queue (where each consumer / producer is its own Process) - I prefer to make them unique by giving each process a unique name via a config file.

UNLESS

I am doing competing consumer in which case the guid approach might be better.

-d

On Mon, Dec 26, 2011 at 10:41 AM, cocowalla <colin.an...@gmail.com> wrote:

Seems I still have a lot to learn about MassTransit!

Should each producer and consumer have a seperate queue? (for example, stick a GUID at the end of the queue name for each producer and consumer instance?

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[Dru Sellers]

you may want to reread this section of the docs as well:

http://docs.masstransit-project.com/en/latest/configuration/config_api.html#basic-options

-d

[Henrik Feldt]

And how do you call that method from an IoC-instantiated service? This is what I mean by 'attribute' e.g. on a class that is stated to be a consumer. Otherwise, how does one make it transient?

[Travis Smith]

I'm not sure I understand what you're trying to do here. You need the
consumer to change data in a producer?

-Travis