queue-delivery-models.md

RedisSMQ / Docs / Queue Delivery Models

Queue Delivery Models

RedisSMQ offers two reliable message delivery models: Point-to-Point and Pub/Sub. Below, we delve into each model, providing detailed explanations, sample code snippets, and best practices for implementation.

Point-to-Point Delivery Model

In the Point-to-Point model, a message is produced to a queue and delivered to a single consumer at a time. This model ensures that each message is processed only once by one consumer.

Creating a Point-to-Point Queue

To create a Point-to-Point queue, use the following code snippet:

const { Queue, EQueueDeliveryModel, EQueueType } = require('redis-smq');

const queue = new Queue();
queue.save(
  'my-queue',
  EQueueType.LIFO_QUEUE,
  EQueueDeliveryModel.POINT_TO_POINT,
  (err, reply) => {
    if (err) {
      console.error('Error creating queue:', err);
    } else {
      console.log('Successfully created queue:', reply);
    }
  }
);

Refer to Queue.save() for additional details.

Publishing a Message to a Point-to-Point Queue

To publish a message to a Point-to-Point queue, use the following:

const { Producer, ProducibleMessage } = require('redis-smq');

const message = new ProducibleMessage();
message.setBody('hello world').setQueue('my-queue');

const producer = new Producer();
producer.run((err) => {
  if (err) {
    console.error('Error running producer:', err);
  } else {
    producer.produce(message, (err, reply) => {
      if (err) {
        console.error('Error producing message:', err);
      } else {
        console.log('Successfully produced message:', reply);
      }
    });
  }
});

Refer to Producer.produce() for more details.

Consuming a Message from a Point-to-Point Queue

To consume a message from a Point-to-Point queue, you can use the following snippet:

const { Consumer } = require('redis-smq');

const consumer = new Consumer();

const messageHandler = (msg, cb) => {
  // Acknowledge the message
  cb();
};

consumer.consume('my-queue', messageHandler, (err) => {
  if (err) {
    console.error('Error adding message handler:', err);
  } else {
    console.log('Message handler added successfully');
  }
});

consumer.run((err) => {
  if (err) {
    console.error('Error running consumer:', err);
  }
});

---

Pub/Sub Delivery Model

Overview

In the Pub/Sub model, messages are delivered to all consumers of a queue. Every consumer receives and processes a copy of the produced message.

Consumer Groups

To consume messages from a Pub/Sub queue, a consumer group is required.

• When publishing a message to a Pub/Sub queue, it is sent to all consumer groups associated with that queue.
• Within each consumer group, only one consumer will receive the message.
• If a message remains unacknowledged for a given time, it will be retried in the same manner as within a Point-to-Point queue.
• If the retry threshold is exceeded, failed messages can be stored, if configured, in the dead-letter queue for that Pub/Sub queue.

Creating a Pub/Sub Queue

To create a Pub/Sub queue, use the following:

const { Queue, EQueueDeliveryModel, EQueueType } = require('redis-smq');

const queue = new Queue();
queue.save(
  'my-pubsub-queue',
  EQueueType.LIFO_QUEUE,
  EQueueDeliveryModel.PUB_SUB,
  (err, reply) => {
    if (err) {
      console.error('Error creating Pub/Sub queue:', err);
    } else {
      console.log('Successfully created Pub/Sub queue:', reply);
    }
  }
);

Refer to Queue.save() for additional details.

Creating Consumer Groups

A consumer group is automatically created when consuming messages from the queue if it does not already exist.

You can also manually create consumer groups using the ConsumerGroups.saveConsumerGroup() method.

Refer to the ConsumerGroups Class for managing consumer groups.

Publishing a Message to a Pub/Sub Queue

Use the following code to publish a message to a Pub/Sub queue:

const { ProducibleMessage, Producer } = require('redis-smq');

const message = new ProducibleMessage();
message.setBody('hello world').setQueue('my-pubsub-queue');

const producer = new Producer();
producer.run((err) => {
  if (err) {
    console.error('Error running producer:', err);
  } else {
    producer.produce(message, (err, reply) => {
      if (err) {
        console.error('Error producing message:', err);
      } else {
        console.log('Successfully produced message:', reply);
      }
    });
  }
});

Note: When producing a message to a Pub/Sub queue, if no consumer groups exist, an error will be returned. Ensure that at least one consumer group is created prior to publishing messages.

Refer to Producer.produce() for more details.

Consuming a Message from a Pub/Sub Queue

To consume a message from a Pub/Sub queue, ensure to specify the consumer group ID:

const { Consumer } = require('redis-smq');

const consumer = new Consumer();

const messageHandler = (msg, cb) => {
  // Acknowledge the message
  cb();
};

consumer.consume(
  { queue: 'my-pubsub-queue', groupId: 'my-app-group-1' },
  messageHandler,
  (err) => {
    if (err) {
      console.error('Error adding message handler:', err);
    } else {
      console.log('Message handler added successfully');
    }
  }
);

consumer.run((err) => {
  if (err) {
    console.error('Error running consumer:', err);
  }
});

Remember to provide the consumer group ID when consuming messages from a Pub/Sub queue.