Message queues provide an asynchronous communications mechanism in which the sender and the receiver of a message do not contact each other. Nor do they need to communicate with the message queue at the same time. When a sender places a messages onto a queue, it is stored until the recipient receives them.
In Magento Commerce, the Message Queue Framework (MQF) is a fully-functional system that allows a module to publish messages to queues. It also creates consumers to receive them asynchronously. The MQF primarily uses RabbitMQ as the messaging broker, which provides a scalable platform for sending and receiving messages. It also includes a mechanism for storing undelivered messages. RabbitMQ is based on the Advanced Message Queuing Protocol (AMQP) 0.9.1 specification.
A basic message queue system can also be set up without using RabbitMQ. In this system, a MySQL adapter
stores messages in the database. Three database tables (
queue_message_status) manage the message queue workload. Cron jobs ensure the consumers are able to receive messages. This solution is not very scalable. RabbitMQ should be used whenever possible.
See Configure message queues for information about setting up the message queue system.
Send a message from the publisher to a queue
The following code sends a message to the queue. The
publish method is defined in
In an MySQL adapter environment, when a message is published to multiple queues, create a single record in
queue_message and multiple records in
queue_message_status: one for each queue. (A join on the
queue_message_status tables is required).
Instantiate a consumer
The procedure for instantiating a consumer differs, depending on which message queue system is being used.
This instantiates a consumer that is defined in a
queue.xml file. The consumer (
customer_created_listener) listens to the queue and receives all new messages. For every message, it invokes
\Magento\Framework\MessageQueue\ConsumerInterface::process($maxNumberOfMessages) to instantiate a consumer.
Perform the following actions:
- Define the queue name associated with current consumer using
$maxNumberOfMessagesmessage records, filtering on the
queue_namefield. You must join on all 3 tables. To accomplish this, you may want to extract fewer records at a time to improve load distribution between multiple consumers.
- Decode the message using topic name taken from the
- Invoke callback
Magento\Framework\MessageQueue\ConsumerConfigurationInterface::getCallbackand pass the decoded data as an argument.
Override topic configuration
The following sample introduces a runtime configuration that allows you to redefine the adapter for a topic.
'queue' => array( 'topics' => array( 'customer.created' => [publisher="default-rabitmq"], 'order.created' => [publisher="default-rabitmq"], ), ),