Message Time-to-Live (TTL)

Use time-to-live in Pub/Sub messages.

Introduction

Dapr enables per-message time-to-live (TTL). This means that applications can set time-to-live per message, and subscribers do not receive those messages after expiration.

All Dapr pub/sub components are compatible with message TTL, as Dapr handles the TTL logic within the runtime. Simply set the ttlInSeconds metadata when publishing a message.

In some components, such as Kafka, time-to-live can be configured in the topic via retention.ms as per documentation. With message TTL in Dapr, applications using Kafka can now set time-to-live per message in addition to per topic.

Native message TTL support

When message time-to-live has native support in the pub/sub component, Dapr simply forwards the time-to-live configuration without adding any extra logic, keeping predictable behavior. This is helpful when the expired messages are handled differently by the component. For example, with Azure Service Bus, where expired messages are stored in the dead letter queue and are not simply deleted.

Supported components

Azure Service Bus

Azure Service Bus supports entity level time-to-live. This means that messages have a default time-to-live but can also be set with a shorter timespan at publishing time. Dapr propagates the time-to-live metadata for the message and lets Azure Service Bus handle the expiration directly.

Non-Dapr subscribers

If messages are consumed by subscribers not using Dapr, the expired messages are not automatically dropped, as expiration is handled by the Dapr runtime when a Dapr sidecar receives a message. However, subscribers can programmatically drop expired messages by adding logic to handle the expiration attribute in the cloud event, which follows the RFC3339 format.

When non-Dapr subscribers use components such as Azure Service Bus, which natively handle message TTL, they do not receive expired messages. Here, no extra logic is needed.

Example

Message TTL can be set in the metadata as part of the publishing request:


curl -X "POST" http://localhost:3500/v1.0/publish/pubsub/TOPIC_A?metadata.ttlInSeconds=120 -H "Content-Type: application/json" -d '{"order-number": "345"}'

from dapr.clients import DaprClient

with DaprClient() as d:
    req_data = {
        'order-number': '345'
    }
    # Create a typed message with content type and body
    resp = d.publish_event(
        pubsub_name='pubsub',
        topic='TOPIC_A',
        data=json.dumps(req_data),
        metadata=(
                     ('ttlInSeconds', '120')
                 )
    )
    # Print the request
    print(req_data, flush=True)

<?php

require_once __DIR__.'/vendor/autoload.php';

$app = \Dapr\App::create();
$app->run(function(\DI\FactoryInterface $factory) {
    $publisher = $factory->make(\Dapr\PubSub\Publish::class, ['pubsub' => 'pubsub']);
    $publisher->topic('TOPIC_A')->publish('data', ['ttlInSeconds' => '120']);
});

See this guide for a reference on the pub/sub API.

Last modified May 13, 2021: Add presentations section (#1480) (7894758)