39. RabbitMQ Binder

39.1 Usage

To use the RabbitMQ binder, you can add it to your Spring Cloud Stream application, by using the following Maven coordinates:

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-stream-binder-rabbit</artifactId>
</dependency>

Alternatively, you can use the Spring Cloud Stream RabbitMQ Starter, as follows:

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-stream-rabbit</artifactId>
</dependency>

39.2 RabbitMQ Binder Overview

The following simplified diagram shows how the RabbitMQ binder operates:

Figure 39.1. RabbitMQ Binder

rabbit binder

By default, the RabbitMQ Binder implementation maps each destination to a TopicExchange. For each consumer group, a Queue is bound to that TopicExchange. Each consumer instance has a corresponding RabbitMQ Consumer instance for its group’s Queue. For partitioned producers and consumers, the queues are suffixed with the partition index and use the partition index as the routing key. For anonymous consumers (those with no group property), an auto-delete queue (with a randomized unique name) is used.

By using the optional autoBindDlq option, you can configure the binder to create and configure dead-letter queues (DLQs) (and a dead-letter exchange DLX, as well as routing infrastructure). By default, the dead letter queue has the name of the destination, appended with .dlq. If retry is enabled (maxAttempts > 1), failed messages are delivered to the DLQ after retries are exhausted. If retry is disabled (maxAttempts = 1), you should set requeueRejected to false (the default) so that failed messages are routed to the DLQ, instead of being re-queued. In addition, republishToDlq causes the binder to publish a failed message to the DLQ (instead of rejecting it). This feature lets additional information (such as the stack trace in the x-exception-stacktrace header) be added to the message in headers. This option does not need retry enabled. You can republish a failed message after just one attempt. Starting with version 1.2, you can configure the delivery mode of republished messages. See the republishDeliveryMode property.

[Important]Important

Setting requeueRejected to true (with republishToDlq=false ) causes the message to be re-queued and redelivered continually, which is likely not what you want unless the reason for the failure is transient. In general, you should enable retry within the binder by setting maxAttempts to greater than one or by setting republishToDlq to true.

See Section 39.3.1, “RabbitMQ Binder Properties” for more information about these properties.

The framework does not provide any standard mechanism to consume dead-letter messages (or to re-route them back to the primary queue). Some options are described in Section 39.6, “Dead-Letter Queue Processing”.

[Note]Note

When multiple RabbitMQ binders are used in a Spring Cloud Stream application, it is important to disable 'RabbitAutoConfiguration' to avoid the same configuration from RabbitAutoConfiguration being applied to the two binders. You can exclude the class by using the @SpringBootApplication annotation.

Starting with version 2.0, the RabbitMessageChannelBinder sets the RabbitTemplate.userPublisherConnection property to true so that the non-transactional producers avoid deadlocks on consumers, which can happen if cached connections are blocked because of a memory alarm on the broker.

39.3 Configuration Options

This section contains settings specific to the RabbitMQ Binder and bound channels.

For general binding configuration options and properties, see the Spring Cloud Stream core documentation.

39.3.1 RabbitMQ Binder Properties

By default, the RabbitMQ binder uses Spring Boot’s ConnectionFactory. Conseuqently, it supports all Spring Boot configuration options for RabbitMQ. (For reference, see the Spring Boot documentation). RabbitMQ configuration options use the spring.rabbitmq prefix.

In addition to Spring Boot options, the RabbitMQ binder supports the following properties:

spring.cloud.stream.rabbit.binder.adminAddresses

A comma-separated list of RabbitMQ management plugin URLs. Only used when nodes contains more than one entry. Each entry in this list must have a corresponding entry in spring.rabbitmq.addresses. Only needed if you use a RabbitMQ cluster and wish to consume from the node that hosts the queue. See Queue Affinity and the LocalizedQueueConnectionFactory for more information.

Default: empty.

spring.cloud.stream.rabbit.binder.nodes

A comma-separated list of RabbitMQ node names. When more than one entry, used to locate the server address where a queue is located. Each entry in this list must have a corresponding entry in spring.rabbitmq.addresses. Only needed if you use a RabbitMQ cluster and wish to consume from the node that hosts the queue. See Queue Affinity and the LocalizedQueueConnectionFactory for more information.

Default: empty.

spring.cloud.stream.rabbit.binder.compressionLevel

The compression level for compressed bindings. See java.util.zip.Deflater.

Default: 1 (BEST_LEVEL).

spring.cloud.stream.binder.connection-name-prefix

A connection name prefix used to name the connection(s) created by this binder. The name is this prefix followed by #n, where n increments each time a new connection is opened.

Default: none (Spring AMQP default).

39.3.2 RabbitMQ Consumer Properties

The following properties are available for Rabbit consumers only and must be prefixed with spring.cloud.stream.rabbit.bindings.<channelName>.consumer..

acknowledgeMode

The acknowledge mode.

Default: AUTO.

autoBindDlq

Whether to automatically declare the DLQ and bind it to the binder DLX.

Default: false.

bindingRoutingKey

The routing key with which to bind the queue to the exchange (if bindQueue is true). For partitioned destinations, -<instanceIndex> is appended.

Default: #.

bindQueue

Whether to bind the queue to the destination exchange. Set it to false if you have set up your own infrastructure and have previously created and bound the queue.

Default: true.

deadLetterQueueName

The name of the DLQ

Default: prefix+destination.dlq

deadLetterExchange

A DLX to assign to the queue. Relevant only if autoBindDlq is true.

Default: 'prefix+DLX'

deadLetterRoutingKey

A dead letter routing key to assign to the queue. Relevant only if autoBindDlq is true.

Default: destination

declareExchange

Whether to declare the exchange for the destination.

Default: true.

delayedExchange

Whether to declare the exchange as a Delayed Message Exchange. Requires the delayed message exchange plugin on the broker. The x-delayed-type argument is set to the exchangeType.

Default: false.

dlqDeadLetterExchange

If a DLQ is declared, a DLX to assign to that queue.

Default: none

dlqDeadLetterRoutingKey

If a DLQ is declared, a dead letter routing key to assign to that queue.

Default: none

dlqExpires

How long before an unused dead letter queue is deleted (in milliseconds).

Default: no expiration

dlqLazy

Declare the dead letter queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue.

Default: false.

dlqMaxLength

Maximum number of messages in the dead letter queue.

Default: no limit

dlqMaxLengthBytes

Maximum number of total bytes in the dead letter queue from all messages.

Default: no limit

dlqMaxPriority

Maximum priority of messages in the dead letter queue (0-255).

Default: none

dlqTtl

Default time to live to apply to the dead letter queue when declared (in milliseconds).

Default: no limit

durableSubscription

Whether the subscription should be durable. Only effective if group is also set.

Default: true.

exchangeAutoDelete

If declareExchange is true, whether the exchange should be auto-deleted (that is, removed after the last queue is removed).

Default: true.

exchangeDurable

If declareExchange is true, whether the exchange should be durable (that is, it survives broker restart).

Default: true.

exchangeType

The exchange type: direct, fanout or topic for non-partitioned destinations and direct or topic for partitioned destinations.

Default: topic.

exclusive

Whether to create an exclusive consumer. Concurrency should be 1 when this is true. Often used when strict ordering is required but enabling a hot standby instance to take over after a failure. See recoveryInterval, which controls how often a standby instance attempts to consume.

Default: false.

expires

How long before an unused queue is deleted (in milliseconds).

Default: no expiration

failedDeclarationRetryInterval

The interval (in milliseconds) between attempts to consume from a queue if it is missing.

Default: 5000

headerPatterns

Patterns for headers to be mapped from inbound messages.

Default: ['*'] (all headers).

lazy

Declare the queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue.

Default: false.

maxConcurrency

The maximum number of consumers.

Default: 1.

maxLength

The maximum number of messages in the queue.

Default: no limit

maxLengthBytes

The maximum number of total bytes in the queue from all messages.

Default: no limit

maxPriority

The maximum priority of messages in the queue (0-255).

Default: none

missingQueuesFatal

When the queue cannot be found, whether to treat the condition as fatal and stop the listener container. Defaults to false so that the container keeps trying to consume from the queue — for example, when using a cluster and the node hosting a non-HA queue is down.

Default: false

prefetch

Prefetch count.

Default: 1.

prefix

A prefix to be added to the name of the destination and queues.

Default: "".

queueDeclarationRetries

The number of times to retry consuming from a queue if it is missing. Relevant only when missingQueuesFatal is true. Otherwise, the container keeps retrying indefinitely.

Default: 3

queueNameGroupOnly

When true, consume from a queue with a name equal to the group. Otherwise the queue name is destination.group. This is useful, for example, when using Spring Cloud Stream to consume from an existing RabbitMQ queue.

Default: false.

recoveryInterval

The interval between connection recovery attempts, in milliseconds.

Default: 5000.

requeueRejected

Whether delivery failures should be re-queued when retry is disabled or republishToDlq is false.

Default: false.

republishDeliveryMode

When republishToDlq is true, specifies the delivery mode of the republished message.

Default: DeliveryMode.PERSISTENT

republishToDlq

By default, messages that fail after retries are exhausted are rejected. If a dead-letter queue (DLQ) is configured, RabbitMQ routes the failed message (unchanged) to the DLQ. If set to true, the binder republishs failed messages to the DLQ with additional headers, including the exception message and stack trace from the cause of the final failure.

Default: false

transacted

Whether to use transacted channels.

Default: false.

ttl

Default time to live to apply to the queue when declared (in milliseconds).

Default: no limit

txSize

The number of deliveries between acks.

Default: 1.

39.3.3 Rabbit Producer Properties

The following properties are available for Rabbit producers only and must be prefixed with spring.cloud.stream.rabbit.bindings.<channelName>.producer..

autoBindDlq

Whether to automatically declare the DLQ and bind it to the binder DLX.

Default: false.

batchingEnabled

Whether to enable message batching by producers. Messages are batched into one message according to the following properties (described in the next three entries in this list): 'batchSize', batchBufferLimit, and batchTimeout. See Batching for more information.

Default: false.

batchSize

The number of messages to buffer when batching is enabled.

Default: 100.

batchBufferLimit

The maximum buffer size when batching is enabled.

Default: 10000.

batchTimeout

The batch timeout when batching is enabled.

Default: 5000.

bindingRoutingKey

The routing key with which to bind the queue to the exchange (if bindQueue is true). Only applies to non-partitioned destinations. Only applies if requiredGroups are provided and then only to those groups.

Default: #.

bindQueue

Whether to bind the queue to the destination exchange. Set it to false if you have set up your own infrastructure and have previously created and bound the queue. Only applies if requiredGroups are provided and then only to those groups.

Default: true.

compress

Whether data should be compressed when sent.

Default: false.

deadLetterQueueName

The name of the DLQ Only applies if requiredGroups are provided and then only to those groups.

Default: prefix+destination.dlq

deadLetterExchange

A DLX to assign to the queue. Relevant only when autoBindDlq is true. Applies only when requiredGroups are provided and then only to those groups.

Default: 'prefix+DLX'

deadLetterRoutingKey

A dead letter routing key to assign to the queue. Relevant only when autoBindDlq is true. Applies only when requiredGroups are provided and then only to those groups.

Default: destination

declareExchange

Whether to declare the exchange for the destination.

Default: true.

delayExpression

A SpEL expression to evaluate the delay to apply to the message (x-delay header). It has no effect if the exchange is not a delayed message exchange.

Default: No x-delay header is set.

delayedExchange

Whether to declare the exchange as a Delayed Message Exchange. Requires the delayed message exchange plugin on the broker. The x-delayed-type argument is set to the exchangeType.

Default: false.

deliveryMode

The delivery mode.

Default: PERSISTENT.

dlqDeadLetterExchange

When a DLQ is declared, a DLX to assign to that queue. Applies only if requiredGroups are provided and then only to those groups.

Default: none

dlqDeadLetterRoutingKey

When a DLQ is declared, a dead letter routing key to assign to that queue. Applies only when requiredGroups are provided and then only to those groups.

Default: none

dlqExpires

How long (in milliseconds) before an unused dead letter queue is deleted. Applies only when requiredGroups are provided and then only to those groups.

Default: no expiration

dlqLazy
Declare the dead letter queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue. Applies only when requiredGroups are provided and then only to those groups.
dlqMaxLength

Maximum number of messages in the dead letter queue. Applies only if requiredGroups are provided and then only to those groups.

Default: no limit

dlqMaxLengthBytes

Maximum number of total bytes in the dead letter queue from all messages. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

dlqMaxPriority

Maximum priority of messages in the dead letter queue (0-255) Applies only when requiredGroups are provided and then only to those groups.

Default: none

dlqTtl

Default time (in milliseconds) to live to apply to the dead letter queue when declared. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

exchangeAutoDelete

If declareExchange is true, whether the exchange should be auto-delete (it is removed after the last queue is removed).

Default: true.

exchangeDurable

If declareExchange is true, whether the exchange should be durable (survives broker restart).

Default: true.

exchangeType

The exchange type: direct, fanout or topic for non-partitioned destinations and direct or topic for partitioned destinations.

Default: topic.

expires

How long (in milliseconds) before an unused queue is deleted. Applies only when requiredGroups are provided and then only to those groups.

Default: no expiration

headerPatterns

Patterns for headers to be mapped to outbound messages.

Default: ['*'] (all headers).

lazy

Declare the queue with the x-queue-mode=lazy argument. See “Lazy Queues”. Consider using a policy instead of this setting, because using a policy allows changing the setting without deleting the queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false.

maxLength

Maximum number of messages in the queue. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

maxLengthBytes

Maximum number of total bytes in the queue from all messages. Only applies if requiredGroups are provided and then only to those groups.

Default: no limit

maxPriority

Maximum priority of messages in the queue (0-255). Only applies if requiredGroups are provided and then only to those groups.

Default: none

prefix

A prefix to be added to the name of the destination exchange.

Default: "".

queueNameGroupOnly

When true, consume from a queue with a name equal to the group. Otherwise the queue name is destination.group. This is useful, for example, when using Spring Cloud Stream to consume from an existing RabbitMQ queue. Applies only when requiredGroups are provided and then only to those groups.

Default: false.

routingKeyExpression

A SpEL expression to determine the routing key to use when publishing messages. For a fixed routing key, use a literal expression, such as routingKeyExpression='my.routingKey' in a properties file or routingKeyExpression: '''my.routingKey''' in a YAML file.

Default: destination or destination-<partition> for partitioned destinations.

transacted

Whether to use transacted channels.

Default: false.

ttl

Default time (in milliseconds) to live to apply to the queue when declared. Applies only when requiredGroups are provided and then only to those groups.

Default: no limit

[Note]Note

In the case of RabbitMQ, content type headers can be set by external applications. Spring Cloud Stream supports them as part of an extended internal protocol used for any type of transport — including transports, such as Kafka (prior to 0.11), that do not natively support headers.

39.4 Retry With the RabbitMQ Binder

When retry is enabled within the binder, the listener container thread is suspended for any back off periods that are configured. This might be important when strict ordering is required with a single consumer. However, for other use cases, it prevents other messages from being processed on that thread. An alternative to using binder retry is to set up dead lettering with time to live on the dead-letter queue (DLQ) as well as dead-letter configuration on the DLQ itself. See “Section 39.3.1, “RabbitMQ Binder Properties”” for more information about the properties discussed here. You can use the following example configuration to enable this feature:

  • Set autoBindDlq to true. The binder create a DLQ. Optionally, you can specify a name in deadLetterQueueName.
  • Set dlqTtl to the back off time you want to wait between redeliveries.
  • Set the dlqDeadLetterExchange to the default exchange. Expired messages from the DLQ are routed to the original queue, because the default deadLetterRoutingKey is the queue name (destination.group). Setting to the default exchange is achieved by setting the property with no value, as shown in the next example.

To force a message to be dead-lettered, either throw an AmqpRejectAndDontRequeueException or set requeueRejected to true (the default) and throw any exception.

The loop continue without end, which is fine for transient problems, but you may want to give up after some number of attempts. Fortunately, RabbitMQ provides the x-death header, which lets you determine how many cycles have occurred.

To acknowledge a message after giving up, throw an ImmediateAcknowledgeAmqpException.

39.4.1 Putting it All Together

The following configuration creates an exchange myDestination with queue myDestination.consumerGroup bound to a topic exchange with a wildcard routing key #:

---
spring.cloud.stream.bindings.input.destination=myDestination
spring.cloud.stream.bindings.input.group=consumerGroup
#disable binder retries
spring.cloud.stream.bindings.input.consumer.max-attempts=1
#dlx/dlq setup
spring.cloud.stream.rabbit.bindings.input.consumer.auto-bind-dlq=true
spring.cloud.stream.rabbit.bindings.input.consumer.dlq-ttl=5000
spring.cloud.stream.rabbit.bindings.input.consumer.dlq-dead-letter-exchange=
---

This configuration creates a DLQ bound to a direct exchange (DLX) with a routing key of myDestination.consumerGroup. When messages are rejected, they are routed to the DLQ. After 5 seconds, the message expires and is routed to the original queue by using the queue name as the routing key, as shown in the following example:

Spring Boot application. 

@SpringBootApplication
@EnableBinding(Sink.class)
public class XDeathApplication {

    public static void main(String[] args) {
        SpringApplication.run(XDeathApplication.class, args);
    }

    @StreamListener(Sink.INPUT)
    public void listen(String in, @Header(name = "x-death", required = false) Map<?,?> death) {
        if (death != null && death.get("count").equals(3L)) {
            // giving up - don't send to DLX
            throw new ImmediateAcknowledgeAmqpException("Failed after 4 attempts");
        }
        throw new AmqpRejectAndDontRequeueException("failed");
    }

}

Notice that the count property in the x-death header is a Long.

39.5 Error Channels

Starting with version 1.3, the binder unconditionally sends exceptions to an error channel for each consumer destination and can also be configured to send async producer send failures to an error channel. See “???” for more information.

RabbitMQ has two types of send failures:

The latter is rare. According to the RabbitMQ documentation "[A nack] will only be delivered if an internal error occurs in the Erlang process responsible for a queue.".

As well as enabling producer error channels (as described in “???”), the RabbitMQ binder only sends messages to the channels if the connection factory is appropriately configured, as follows:

  • ccf.setPublisherConfirms(true);
  • ccf.setPublisherReturns(true);

When using Spring Boot configuration for the connection factory, set the following properties:

  • spring.rabbitmq.publisher-confirms
  • spring.rabbitmq.publisher-returns

The payload of the ErrorMessage for a returned message is a ReturnedAmqpMessageException with the following properties:

  • failedMessage: The spring-messaging Message<?> that failed to be sent.
  • amqpMessage: The raw spring-amqp Message.
  • replyCode: An integer value indicating the reason for the failure (for example, 312 - No route).
  • replyText: A text value indicating the reason for the failure (for example, NO_ROUTE).
  • exchange: The exchange to which the message was published.
  • routingKey: The routing key used when the message was published.

For negatively acknowledged confirmations, the payload is a NackedAmqpMessageException with the following properties:

  • failedMessage: The spring-messaging Message<?> that failed to be sent.
  • nackReason: A reason (if available — you may need to examine the broker logs for more information).

There is no automatic handling of these exceptions (such as sending to a dead-letter queue). You can consume these exceptions with your own Spring Integration flow.

39.6 Dead-Letter Queue Processing

Because you cannot anticipate how users would want to dispose of dead-lettered messages, the framework does not provide any standard mechanism to handle them. If the reason for the dead-lettering is transient, you may wish to route the messages back to the original queue. However, if the problem is a permanent issue, that could cause an infinite loop. The following Spring Boot application shows an example of how to route those messages back to the original queue but moves them to a third “parking lot” queue after three attempts. The second example uses the RabbitMQ Delayed Message Exchange to introduce a delay to the re-queued message. In this example, the delay increases for each attempt. These examples use a @RabbitListener to receive messages from the DLQ. You could also use RabbitTemplate.receive() in a batch process.

The examples assume the original destination is so8400in and the consumer group is so8400.

39.6.1 Non-Partitioned Destinations

The first two examples are for when the destination is not partitioned:

@SpringBootApplication
public class ReRouteDlqApplication {

    private static final String ORIGINAL_QUEUE = "so8400in.so8400";

    private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

    private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

    private static final String X_RETRIES_HEADER = "x-retries";

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
        System.out.println("Hit enter to terminate");
        System.in.read();
        context.close();
    }

    @Autowired
    private RabbitTemplate rabbitTemplate;

    @RabbitListener(queues = DLQ)
    public void rePublish(Message failedMessage) {
        Integer retriesHeader = (Integer) failedMessage.getMessageProperties().getHeaders().get(X_RETRIES_HEADER);
        if (retriesHeader == null) {
            retriesHeader = Integer.valueOf(0);
        }
        if (retriesHeader < 3) {
            failedMessage.getMessageProperties().getHeaders().put(X_RETRIES_HEADER, retriesHeader + 1);
            this.rabbitTemplate.send(ORIGINAL_QUEUE, failedMessage);
        }
        else {
            this.rabbitTemplate.send(PARKING_LOT, failedMessage);
        }
    }

    @Bean
    public Queue parkingLot() {
        return new Queue(PARKING_LOT);
    }

}
@SpringBootApplication
public class ReRouteDlqApplication {

    private static final String ORIGINAL_QUEUE = "so8400in.so8400";

    private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

    private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

    private static final String X_RETRIES_HEADER = "x-retries";

    private static final String DELAY_EXCHANGE = "dlqReRouter";

    public static void main(String[] args) throws Exception {
        ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
        System.out.println("Hit enter to terminate");
        System.in.read();
        context.close();
    }

    @Autowired
    private RabbitTemplate rabbitTemplate;

    @RabbitListener(queues = DLQ)
    public void rePublish(Message failedMessage) {
        Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
        Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
        if (retriesHeader == null) {
            retriesHeader = Integer.valueOf(0);
        }
        if (retriesHeader < 3) {
            headers.put(X_RETRIES_HEADER, retriesHeader + 1);
            headers.put("x-delay", 5000 * retriesHeader);
            this.rabbitTemplate.send(DELAY_EXCHANGE, ORIGINAL_QUEUE, failedMessage);
        }
        else {
            this.rabbitTemplate.send(PARKING_LOT, failedMessage);
        }
    }

    @Bean
    public DirectExchange delayExchange() {
        DirectExchange exchange = new DirectExchange(DELAY_EXCHANGE);
        exchange.setDelayed(true);
        return exchange;
    }

    @Bean
    public Binding bindOriginalToDelay() {
        return BindingBuilder.bind(new Queue(ORIGINAL_QUEUE)).to(delayExchange()).with(ORIGINAL_QUEUE);
    }

    @Bean
    public Queue parkingLot() {
        return new Queue(PARKING_LOT);
    }

}

39.6.2 Partitioned Destinations

With partitioned destinations, there is one DLQ for all partitions. We determine the original queue from the headers.

republishToDlq=false

When republishToDlq is false, RabbitMQ publishes the message to the DLX/DLQ with an x-death header containing information about the original destination, as shown in the following example:

@SpringBootApplication
public class ReRouteDlqApplication {

	private static final String ORIGINAL_QUEUE = "so8400in.so8400";

	private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

	private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

	private static final String X_DEATH_HEADER = "x-death";

	private static final String X_RETRIES_HEADER = "x-retries";

	public static void main(String[] args) throws Exception {
		ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
		System.out.println("Hit enter to terminate");
		System.in.read();
		context.close();
	}

	@Autowired
	private RabbitTemplate rabbitTemplate;

	@SuppressWarnings("unchecked")
	@RabbitListener(queues = DLQ)
	public void rePublish(Message failedMessage) {
		Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
		Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
		if (retriesHeader == null) {
			retriesHeader = Integer.valueOf(0);
		}
		if (retriesHeader < 3) {
			headers.put(X_RETRIES_HEADER, retriesHeader + 1);
			List<Map<String, ?>> xDeath = (List<Map<String, ?>>) headers.get(X_DEATH_HEADER);
			String exchange = (String) xDeath.get(0).get("exchange");
			List<String> routingKeys = (List<String>) xDeath.get(0).get("routing-keys");
			this.rabbitTemplate.send(exchange, routingKeys.get(0), failedMessage);
		}
		else {
			this.rabbitTemplate.send(PARKING_LOT, failedMessage);
		}
	}

	@Bean
	public Queue parkingLot() {
		return new Queue(PARKING_LOT);
	}

}

republishToDlq=true

When republishToDlq is true, the republishing recoverer adds the original exchange and routing key to headers, as shown in the following example:

@SpringBootApplication
public class ReRouteDlqApplication {

	private static final String ORIGINAL_QUEUE = "so8400in.so8400";

	private static final String DLQ = ORIGINAL_QUEUE + ".dlq";

	private static final String PARKING_LOT = ORIGINAL_QUEUE + ".parkingLot";

	private static final String X_RETRIES_HEADER = "x-retries";

	private static final String X_ORIGINAL_EXCHANGE_HEADER = RepublishMessageRecoverer.X_ORIGINAL_EXCHANGE;

	private static final String X_ORIGINAL_ROUTING_KEY_HEADER = RepublishMessageRecoverer.X_ORIGINAL_ROUTING_KEY;

	public static void main(String[] args) throws Exception {
		ConfigurableApplicationContext context = SpringApplication.run(ReRouteDlqApplication.class, args);
		System.out.println("Hit enter to terminate");
		System.in.read();
		context.close();
	}

	@Autowired
	private RabbitTemplate rabbitTemplate;

	@RabbitListener(queues = DLQ)
	public void rePublish(Message failedMessage) {
		Map<String, Object> headers = failedMessage.getMessageProperties().getHeaders();
		Integer retriesHeader = (Integer) headers.get(X_RETRIES_HEADER);
		if (retriesHeader == null) {
			retriesHeader = Integer.valueOf(0);
		}
		if (retriesHeader < 3) {
			headers.put(X_RETRIES_HEADER, retriesHeader + 1);
			String exchange = (String) headers.get(X_ORIGINAL_EXCHANGE_HEADER);
			String originalRoutingKey = (String) headers.get(X_ORIGINAL_ROUTING_KEY_HEADER);
			this.rabbitTemplate.send(exchange, originalRoutingKey, failedMessage);
		}
		else {
			this.rabbitTemplate.send(PARKING_LOT, failedMessage);
		}
	}

	@Bean
	public Queue parkingLot() {
		return new Queue(PARKING_LOT);
	}

}

39.7 Partitioning with the RabbitMQ Binder

RabbitMQ does not support partitioning natively.

Sometimes, it is advantageous to send data to specific partitions — for example, when you want to strictly order message processing, all messages for a particular customer should go to the same partition.

The RabbitMessageChannelBinder provides partitioning by binding a queue for each partition to the destination exchange.

The following Java and YAML examples show how to configure the producer:

Producer. 

@SpringBootApplication
@EnableBinding(Source.class)
public class RabbitPartitionProducerApplication {

    private static final Random RANDOM = new Random(System.currentTimeMillis());

    private static final String[] data = new String[] {
            "abc1", "def1", "qux1",
            "abc2", "def2", "qux2",
            "abc3", "def3", "qux3",
            "abc4", "def4", "qux4",
            };

    public static void main(String[] args) {
        new SpringApplicationBuilder(RabbitPartitionProducerApplication.class)
            .web(false)
            .run(args);
    }

    @InboundChannelAdapter(channel = Source.OUTPUT, poller = @Poller(fixedRate = "5000"))
    public Message<?> generate() {
        String value = data[RANDOM.nextInt(data.length)];
        System.out.println("Sending: " + value);
        return MessageBuilder.withPayload(value)
                .setHeader("partitionKey", value)
                .build();
    }

}

application.yml. 

    spring:
      cloud:
        stream:
          bindings:
            output:
              destination: partitioned.destination
              producer:
                partitioned: true
                partition-key-expression: headers['partitionKey']
                partition-count: 2
                required-groups:
                - myGroup

[Note]Note

The configuration in the prececing example uses the default partitioning (key.hashCode() % partitionCount). This may or may not provide a suitably balanced algorithm, depending on the key values. You can override this default by using the partitionSelectorExpression or partitionSelectorClass properties.

The required-groups property is required only if you need the consumer queues to be provisioned when the producer is deployed. Otherwise, any messages sent to a partition are lost until the corresponding consumer is deployed.

The following configuration provisions a topic exchange:

part exchange

The following queues are bound to that exchange:

part queues

The following bindings associate the queues to the exchange:

part bindings

The following Java and YAML examples continue the previous examples and show how to configure the consumer:

Consumer. 

@SpringBootApplication
@EnableBinding(Sink.class)
public class RabbitPartitionConsumerApplication {

    public static void main(String[] args) {
        new SpringApplicationBuilder(RabbitPartitionConsumerApplication.class)
            .web(false)
            .run(args);
    }

    @StreamListener(Sink.INPUT)
    public void listen(@Payload String in, @Header(AmqpHeaders.CONSUMER_QUEUE) String queue) {
        System.out.println(in + " received from queue " + queue);
    }

}

application.yml. 

    spring:
      cloud:
        stream:
          bindings:
            input:
              destination: partitioned.destination
              group: myGroup
              consumer:
                partitioned: true
                instance-index: 0

[Important]Important

The RabbitMessageChannelBinder does not support dynamic scaling. There must be at least one consumer per partition. The consumer’s instanceIndex is used to indicate which partition is consumed. Platforms such as Cloud Foundry can have only one instance with an instanceIndex.