Skip to content

message-exchanges.md

Latest commit

 

History

History
194 lines (144 loc) · 5.09 KB

message-exchanges.md

File metadata and controls

194 lines (144 loc) · 5.09 KB

RedisSMQ / Documentation / Message Exchanges

Message Exchanges

Exchanges route messages to queues based on rules. Instead of sending directly to a queue, you publish to an exchange which handles the routing.

When to Use Exchanges

Use Case Best Choice
Send to one specific queue Direct queue (setQueue())
Route to queues by exact key Direct exchange
Route by patterns (user.*, order.#) Topic exchange
Broadcast to multiple queues Fanout exchange

Performance Tip: setQueue() is fastest. Use exchanges only when you need their routing features.

Exchange Types

1. Direct Exchange

Routes to queues with exact routing key matches.

const msg = new ProducibleMessage()
  .setDirectExchange('payments')
  .setExchangeRoutingKey('payment.processed') // Must match exactly
  .setBody({ amount: 99.99 });

2. Topic Exchange

Routes using pattern matching:

  • * = one word
  • # = zero or more words
  • Words separated by dots
const msg = new ProducibleMessage()
  .setTopicExchange('events')
  .setExchangeRoutingKey('user.login.success')
  .setBody({ userId: 123 });

// Patterns that would match:
// 'user.login.success' → 'user.*.success', 'user.#', '*.login.*'

3. Fanout Exchange

Broadcasts to all bound queues.

const msg = new ProducibleMessage()
  .setFanoutExchange('alerts') // No routing key needed
  .setBody({ alert: 'System down!' });

Setup

Bind Queues to Exchanges

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

// Direct exchange (exact match)
const direct = RedisSMQ.createDirectExchange();
direct.bindQueue('email-queue', 'notifications', 'welcome.email', (err) => {
  if (err) console.error('Bind failed:', err);
});

// Topic exchange (pattern match)
const topic = RedisSMQ.createTopicExchange();
topic.bindQueue('audit-queue', 'events', 'user.*', (err) => {
  if (err) console.error('Bind failed:', err);
});

// Fanout exchange (broadcast)
const fanout = RedisSMQ.createFanoutExchange();
fanout.bindQueue('sms-queue', 'alerts', (err) => {
  if (err) console.error('Bind failed:', err);
});

Note: Exchanges are created automatically when first bound.

Sending Messages

Direct to Queue (Fastest)

const msg = new ProducibleMessage()
  .setQueue('orders') // Direct delivery
  .setBody({ item: 'Book' });

Through Exchange

const msg = new ProducibleMessage()
  .setTopicExchange('events')
  .setExchangeRoutingKey('order.created') // REQUIRED for direct/topic
  .setBody({ orderId: 456 });

producer.produce(msg, (err, messageIds) => {
  if (err) {
    if (err.message.includes('No matching queues')) {
      console.log('No queues bound to this routing key');
    }
  } else {
    console.log(`Sent to ${messageIds.length} queue(s)`);
  }
});

Managing Exchanges

Check Bindings

direct.getRoutingKeys('notifications', (err, keys) => {
  console.log('Bound routing keys:', keys);
  // Returns: ['welcome.email', 'password.reset', ...]
});

Unbind Queues

// Direct/Topic exchange
direct.unbindQueue('email-queue', 'notifications', 'welcome.email', (err) => {
  if (!err) console.log('Queue unbound');
});

// Fanout exchange
fanout.unbindQueue('sms-queue', 'alerts', (err) => {
  if (!err) console.log('Queue unbound');
});

Delete Exchange

// Only works when no queues are bound
direct.delete('notifications', (err) => {
  if (err) console.error('Delete failed:', err);
  else console.log('Exchange deleted');
});

Common Patterns

Event System

// Publisher
msg.setTopicExchange('app-events');
msg.setExchangeRoutingKey('user.profile.updated');

// Subscribers bind with patterns:
// 'user.*'       - All user events
// '*.updated'    - All update events
// 'user.profile.*' - Profile-related events

Multi-Channel Notifications

// Bind multiple queues
fanout.bindQueue('email-service', 'notifications', callback);
fanout.bindQueue('sms-service', 'notifications', callback);
fanout.bindQueue('push-service', 'notifications', callback);

// Send once, delivers to all
msg.setFanoutExchange('notifications');
msg.setBody({ message: 'Sale starts now!' });

Best Practices

  1. Use setQueue() for simple cases - It's faster and simpler
  2. Plan your routing key structure - Use dots for hierarchy: domain.entity.action
  3. Check for matching queues - Handle "No matching queues" errors gracefully
  4. Set up bindings at startup - Configure routing before sending messages
  5. Monitor exchange usage - Too many patterns can impact performance

Related Documentation: