SpringBoot doesn’t offer a very easy way of handling multiple RabbitMQ servers without introducing the complexity of SpringCloud Stream or the need to manually provide multiple connection factories in code.

The spring-multirabbit library solves this problem, requiring none or minimal changes to the code and very simple extension of the configuration.

How to use?

Add spring-boot-starter-amqp and spring-multirabbit into the dependencies of the project. Bellow, an example for Maven.

<dependency>
    <groupId>com.mytaxi.spring.multirabbit</groupId>
    <artifactId>spring-multirabbit</artifactId>
    <version>2.7.0</version>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-amqp</artifactId>
</dependency>

Update the configuration to introduce the additional servers.

The example below has a default server configured at spring.rabbitmq and introduces two additional servers configured under spring.multirabbitmq.serverB and spring.multirabbitmq.thirdServer.

spring.rabbitmq.host:10.0.0.10
spring.rabbitmq.port:5672
spring.multirabbitmq.serverB.host:msgbroker.somedomain.com
spring.multirabbitmq.serverB.port:5672
spring.multirabbitmq.thirdServer.host:173.49.20.18
spring.multirabbitmq.thirdServer.port:5672

For the sake of simplification, no credentials or any other configuration is being provided. However, all the possible parameters that are available under spring.rabbitmq are available for the additional servers.

Versions

The correct version of spring-multirabbit depends on the version of SpringBoot:

• SpringBoot 2.7.x -> spring-multirabbit:2.7.0
• SpringBoot 2.6.x -> spring-multirabbit:2.6.0
• SpringBoot 2.5.x -> spring-multirabbit:2.5.0

There are some cases where SpringBoot’s APIs changes break compatibility with spring-multirabbit, and it requires another version, however this is very unlikely to happen. More info regarding compatibility in the project’s wiki page.

Listeners

The spring-multirabbit library creates necessary beans using the same names as the servers provided from the configuration. Thus, you can start listening to messages from the specified server by simply setting containerFactory=[servername].

@RabbitListener(queues = "someQueue")
void listenToDefaultServer(...){...} // Listening to server serverB

@RabbitListener(queues = "someQueueName", containerFactory = "serverB")
void listenToServerB(...){...} // Listening to server thirdServer

@RabbitListener(queues = "anotherQueueName", containerFactory = "thirdServer")
void listenToThirdServer(...){...}

In the above example, the 3 servers are being listened: the default one (which does not require any binding), serverB and thirdServer.

RabbitTemplate

To send or receive messages using RabbitTemplate, it’s necessary to indicate the context, done programmatically with SimpleResourceHolder. This class is able to bind the specific connection factory to the running thread. It’s necessary to bind and unbind it afterward, so the thread does not keep the reference.

@Autowired
private RabbitTemplate template;

void sendMessageToDefaultServer(){
    template.convertAndSend(...);
}

void sendMessageToServerB(){
    SimpleResourceHolder.bind(template.getConnectionFactory(),"serverB");
    template.convertAndSend(...);
    SimpleResourceHolder.unbind(template.getConnectionFactory());
}

void sendMessageToThirdServer(){
    SimpleResourceHolder.bind(template.getConnectionFactory(),"thirdServer");
    template.convertAndSend(...);
    SimpleResourceHolder.unbind(template.getConnectionFactory());
}

Note that it would be a good practice to have a try-catch block to unbind it inside the finally block, but for the simplification, that was not done in the example.

Yet for the simplification, spring-multirabbit brings a utility class for context handling. The class ConnectionFactoryContextWrapper is provided as a bean and wraps the logic of binding and unbinding the connection factory while providing a simple way to execute a Runnable or Callable. The example above would then be rewritten as below:

@Autowired
private RabbitTemplate template;

@Autowired
private ConnectionFactoryContextWrapper contextWrapper;

void sendMessageToDefaultServer(){
    template.convertAndSend(...);
}

void sendMessageToServerB(){
    contextWrapper.run("serverB",()->template.convertAndSend(...));
}

void sendMessageToThirdServer(){
    contextWrapper.run("thirdServer",()->template.convertAndSend(...));
}

More examples

For more examples, access the example modules in the source code.

Source Code

spring-multirabbit is open source and available at https://github.com/freenowtech/spring-multirabbit. Feel free to contribute.