Change concurrent-consumers on the fly

[flopezluis]

Is there any way to increase the number of consumers without stopping Tomcat?

Like hot deploy, so you can change the configuration file:
from <int-amqp:inbound-channel-adapter concurrent-consumers="10"
to <int-amqp:inbound-channel-adapter concurrent-consumers="30"

Thanks

[Gary Russell]

Yes.

Declare an external listener container and inject it into the adapter...

    <int-amqp:inbound-channel-adapter channel="fromRabbit" 
		listener-container="listener.container" />
	
    <bean id="listenerContainer" class="org.springframework.amqp.rabbit.listener.SimpleMessageListenerContainer">
        <property name="channelTransacted" value="false" />
        <property name="concurrentConsumers" value="2" />
        <property name="prefetchCount" value="1" />
        <property name="connectionFactory" ref="connectionFactory" />
        <property name="acknowledgeMode" value="AUTO" />
        <property name="queues" value="si.test.queue" />
        <property name="autoStartup" value="true" />
    </bean>

Get a reference to the SMLC, then execute stop(), change the consumers, and start()...

@Autowire private SimpleMessageListenerContainer container;

...

    container.stop();
    container.setConcurrentConsumers(newConsumers);
    container.start();

Or, use a <control-bus/> and send "@listenerContainer.stop()" etc to it.

[flopezluis]

Great answer, Thanks a lot!!

[assaf27]

Hi,

Trying the control bus method above failed for me. I think setConcurrentConsumers() need to be marked with @ManagedOperation fort this to work, no?
Maybe it's even better to extend SimpleMessageListenerContainer and add a method that exectues the three steps (stop, reconfigure and start)?

[Gary Russell]

You are correct; that method is not available via the control-bus.

Yes, a subclass would work (with the control-bus too).

Please be aware that we recently found an issue (https://jira.springsource.org/browse/AMQP-275) where a race condition can cause some messages to remain un-ack'd when stopping the container. They are not lost, but won't be redelivered until the connection is reset.

This is fixed in 1.1.3.RELEASE which should be available later this week.

[Gary Russell]

spring-amqp 1.1.3.RELEASE, including this fix, is now available

http://www.springsource.org/spring-amqp