Anypoint MQ ACK and NACK Operations

Acknowledging a message (ACK) informs the broker that the message has been processed and must be removed from the queue to prevent redelivery. Not acknowledging a message (NACK) tells the broker to not process the message and to return the message to the queue for redelivery to any available consumer.

The Anypoint MQ connector provides three acknowledgment configurations: Immediate, Automatic, and Manual.

Immediate Acknowledgment

Use the IMMEDIATE acknowledgment mode to acknowledge messages as your app consumes them and before processing them.

When Anypoint MQ acknowledges a message, it removes the message from the queue and doesn’t redeliver it if an error occurs during processing.

If the app restarts between being acknowledged and dispatched, the message might not be available again because it was deleted from the queue. To prevent message deletion until after processing, use the AUTO or MANUAL acknowledgment mode instead.

If an error occurs during message processing using IMMEDIATE mode, Anypoint MQ throws an ANYPOINT-MQ:ACKING error. To manage errors without losing messages, use a dead letter queue.

Automatic Acknowledgment

Use the AUTO acknowledgment mode to acknowledge a received message automatically only if the flow execution finishes successfully.

If an error occurs during flow execution, execution terminates, and the message is returned to the queue for redelivery.

Manual Acknowledgment

Use the MANUAL acknowledgment mode to delegate all responsibility to the app logic to decide when to acknowledge the message.

With this configuration, every message received has an AnypointMQMessageContext object in the Mule message attributes that identifies this message uniquely for a given connection.

Acknowledgment Timeout

When using either AUTO or MANUAL acknowledgment modes, you can use the acknowledgementTimeout parameter to control how long the message remains in-flight waiting to be acknowledged, before automatically returning to the queue.

The app must execute either an ACK or NACK operation on the message before the timeout expires.

When using acknowledgementTimeout, consider expected app-time processing, including time for unexpected delays, such as external systems delay and app back-pressure due to high load. For example, if you expect the consumed message to be processed in 10 seconds, set the acknowledgementTimeout to a minimum of 15 seconds.

Execute an ACK Operation

Acknowledging a message informs the broker that the message has been processed and must be removed from the queue to prevent redelivery.

The`AnypointMQMessageContext` object identifies the message to pass on to the anypoint-mq:ack operation:

<flow name="consumerWithManualAck">
    <anypoint-mq:consume
       destination="${destination}"
       acknowledgementMode="MANUAL"
       config-ref="AMQ_Config"/>

    <!-- Process messages without modifying the payload-->
    <jms:publish config="JMS_config" destination="${bridgedDestination}">

    <anypoint-mq:ack messageContext="#[attributes]" config-ref="AMQ_Config"/>
</flow>

If a non-void operation is invoked during message processing, the payload and attributes of the Mule message are modified. To perform an ACK operation after processing, you must save the original attributes in a variable.

To save attributes to use later, use the target and targetValue parameters to store the whole message in a variable:

<flow name="consumerWithManualAck">
    <anypoint-mq:consume destination="${destination}"
                 acknowledgementMode="MANUAL"
                 config-ref="AMQ_Config"
                 target="mqMessage"
                 targetValue="#[message]"/>

    <!--Do message processing changing the payload-->
    <http:request method="POST" path="/invoicesProcessing" config-ref="httpRequestConfig">
            <http:body>#[vars.mqMessage.payload]</http:body>
    </http:request>

    <anypoint-mq:ack messageContext="#[vars.mqMessage.attributes]" config-ref="AMQ_Config"/>
</flow>

Execute a NACK Operation

Not acknowledging a message informs the broker that the message was not processed successfully and commands the broker to return the message to the queue for redelivery to any available consumer.

The AnypointMQMessageContext object that identifies the message is passed to the anypoint-mq:nack operation:

<flow name="consumerWithManualAck">
    <anypoint-mq:consume
                 destination="${destination}"
                 acknowledgementMode="MANUAL"
                 config-ref="AMQ_Config"/>

    <!--Do message processing-->
    <logger message="#[payload]">

    <anypoint-mq:nack messageContext="#[attributes]" config-ref="AMQ_Config"/>
</flow>