several Rebus subscribers for the same event

Today I’ve learned that Rebus events are not sent for all subscriber instances by default.

When you subcsribe to an event, you’re binding the topic to the subscriber’s input queue. If you have two distinct subscribers, they should have different input queue names, and then they will each get a copy of the event

So you should configure Rebus to allow subscriber1 and subscriber2 to consume the same SampleEvent message.

There is Rebus multiple subscribers sample available.

The sample shows dedicated input queue configuration for each subscriber and publish messages instead of sending.

To have the same message consumed by two subscribers you have to configure:

unique queue per subscriber

_.Transport(t => t.UseSqlServer(transportOptions, queue));

the queue name should be unique for each subscriber
run IBus.Subscribe<T> when subscriber is ready for incoming messages. The Subscribe should be executed to configure topic to address subscription.
IBus.Publish should be executed to broadcast event to all queues
Type based routing on each subscriber for the same destination address

_.Routing(r => r.TypeBased().Map<SampleEvent>("sampleEvent"));
centralized subscriptions storage (optional)

_.Subscriptions(s => s.StoreInSqlServer(connection, "sampleEventSubs", isCentralized: true));

however the Azure bus sample does not require this step e.g.

The centralized subscriptions SQL store has list of subscribers queue names (aka addresses) and message types (aka topics) to be published to.

The Azure Service Bus has in-built topic routing feature to copy event for each subscriber and this feature is used by Rebus.