Scheduled and delayed messages:Routing with TTL and dead-letter exchange in RabbitMQ

The challenge of scheduling events without plugins

Often, we need to delay message delivery in our messaging architectures: for example, sending a reminder email 2 hours after account creation, or retrying a temporarily failed transaction after a planned 10-minute delay. While RabbitMQ offers an official delayed messages plugin (rabbitmq-delayed-message-exchange), it is not always available or permitted in managed cloud environments (like AWS Amazon MQ). The onkai-unified-bus bypasses this limitation by designing a native topology based on message Time-To-Live (TTL) expiration directed toward a Dead-Letter Exchange (DLX).

The delayed message routing flow

To delay a message, we create an indirect routing flow:

• Publish the event to a temporary queue that has no active consumers.
• Configure a x-message-ttl limit on this queue equivalent to the desired delay.
• Configure a Dead-Letter Exchange (DLX) pointing to the final target exchange.
• When the TTL expires, RabbitMQ automatically evicts the message from the temporary queue and routes it to the exchange configured in the DLX.

package main

import (
    "context"
    "fmt"
    "github.com/rabbitmq/amqp091-go"
)

// SetupDelayedTopology declares a consumer-less queue with TTL and DLX arguments
func SetupDelayedTopology(ch *amqp091_go.Channel, delayMs int) (string, error) {
    delayQueueName := fmt.Sprintf("delay-queue-%dms", delayMs)

    // Declares the queue with specific TTL and DLX configurations
    _, err := ch.QueueDeclare(
        delayQueueName,
        true,  // durable
        false, // auto-delete
        false, // exclusive
        false, // no-wait
        amqp091_go.Table{
            "x-message-ttl":               int32(delayMs), // Retention period
            "x-dead-letter-exchange":      "main-event-exchange", // Destination post expiration
            "x-dead-letter-routing-key":   "notifications.send",
        },
    )
    return delayQueueName, err
}

Benefits of the native approach

Using this routing pattern:

• Eliminates dependencies on third-party broker plugins.
• Leverages the native persistence and reliability guarantees of the RabbitMQ engine.
• Supports varied delay durations by declaring queues with specific TTLs on the fly.

Technical terms demystified

• TTL (Time-To-Live): The maximum period of time a message can remain in a queue before being discarded or moved to a dead-letter exchange.
• Dead-Letter Exchange (DLX): A normal RabbitMQ exchange where expired, rejected, or failed messages are routed automatically.
• Delayed Topology: An arrangement of exchanges and queues configured to temporarily hold messages for a controlled time.

link: https://github.com/wesleyskap/onkai-unified-bus