Direct#
The Direct Subject is the basic way to route messages in NATS. Its essence is very simple: a subject
sends messages to all consumers subscribed to it.
Scaling#
If one subject
is being listened to by several consumers with the same queue group
, the message will go to a random consumer each time.
Thus, NATS can independently balance the load on queue consumers. You can increase the processing speed of the message flow from the queue by simply launching additional instances of the consumer service. You don't need to make changes to the current infrastructure configuration: NATS will take care of how to distribute messages between your services.
Example#
The Direct Subject is the type used in FastStream by default: you can simply declare it as follows
Full example:
Consumer Announcement#
To begin with, we have declared several consumers for two subjects
: test-subj-1
and test-subj-2
:
Note
Note that all consumers are subscribed using the same queue_group
. Within the same service, this does not make sense, since messages will come to these handlers in turn. Here, we emulate the work of several consumers and load balancing between them.
Message Distribution#
Now the distribution of messages between these consumers will look like this:
The message 1
will be sent to handler1
or handler2
because they are listening to one subject
within one queue group
.
Message 2
will be sent similarly to message 1
.
The message 3
will be sent to handler3
because it is the only one listening to test-subj-2
.