queue-delivery-models.md

RedisSMQ / Docs / Queue Delivery Models

Queue Delivery Models

When it comes to message delivery RedisSMQ provides 2 reliable models: Point-2-Point and Pub/Sub.

Point-2-Point Delivery Model

In the Point-2-Point model, a message is produced to a Point-2-Point queue and then delivered to and consumed by at a time only one consumer.

Creating a Point-2-Point Queue

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(err);
  else console.log('Successfully created', reply)
})

See Queue.save() for more details.

Publishing a Message to a Point-2-Point Queue

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(err);
  else producer.produce(message, (err, reply) => {
    if (err) console.error(err);
    else console.log('Successfully produced', reply);
  })
})

See Producer.produce() for more details.

Consuming a message from a Point-2-Point Queue

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

const consumer = new Consumer();

const messageHandler = (msg, cb) => cb(); // acknowledging
consumer.consume('my-queue', messageHandler, (err) => {
  if (err) console.error(err);
  else console.log('MessageHandler added');
});
consumer.run((err) => {
  if (err) console.error(err);
})

Pub/Sub Delivery Model

Overview

In the Pub/Sub model, on the other hand, a message is delivered to and consumed by all consumers of a Pub/Sub queue.

From a high-level view the Pub/Sub model maybe illustrated as shown in the diagram above.

Each 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.

In fact, when publishing a message to a pub/sub queue, the message is published to all consumer groups of the given queue.

Within a consumer group, only one consumer receives the message.

For a consumer group, unacknowledged messages are retried in the same manner as for a Point-2-Point queue.

When retryTreshold is exceeded failed messages from all consumer groups are stored, if configured to do so, in the dead-letter-queue of the given Pub/Sub queue.

Creating a Pub/Sub Queue

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(err);
  else console.log('Successfully created', reply)
})

See Queue.save() for more details.

Creating Consumer Groups

If it does not exist a consumer group of a given queue is created automatically when consuming messages from the queue.

Consumer groups may be also created manually using the ConsumerGroups.saveConsumerGroup() method.

See ConsumerGroups Class for managing consumer groups.

Publishing 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(err);
  else producer.produce(message, (err, reply) => {
    if (err) console.error(err);
    else console.log('Successfully produced', reply);
  })
})

When producing a message to a Pub/Sub queue, if the queue has no consumer groups an error will be returned.

So make sure the queue has at least one consumer group before publishing messages.

See Producer.produce() for more details.

Consuming a message from a Pub/Sub Queue

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

const consumer = new Consumer();

const messageHandler = (msg, cb) => cb(); // acknowledging
consumer.consume({ queue: 'my-pubsub-queue', groupId: 'my-app-group-1' }, messageHandler, (err) => {
  if (err) console.error(err);
  else console.log('MessageHandler added');
});
consumer.run((err) => {
  if (err) console.error(err);
})

Please do not forget to provide the consumer group ID when consuming messages from a Pub/Sub queue.