Pub/Sub is a messaging paradigm that allows publishers to send messages to subscribers through a broker. In Drupal, it allows content like nodes to be published from one site to another. Key aspects of Pub/Sub in Drupal include topics defined by views, filtering content via rules, and supporting push and pull of content between loosely coupled systems. It can integrate with other modules via hooks and is used on a case study site to sync over 57k nodes across 21 channels.

1. Publish /
Subscribe
Alexandru Badiu

2. Me
Alexandru Badiu
Drupal user and contributor since 2003
Adulmec LLC
Drupal Romania
Drupal.ro

3. We’re goning to talk about
What is Pub/Sub
Pub/Sub in Drupal
Basic usage
Advanced features
Integration with 3rd party modules
Case study: Urbo.ro

4. What is Pub/Sub?
Messaging paradigm
Sibling of Message queues
Publisher, Subscriber, Broker
Decoupled
Topic based
Content based
Push
Pull

5. What is Pub/Sub?
Advantages
Loosely coupled
Scalable
Disadvantages
Not so scalable on large deployments
Loosely coupled

6. What is Pub/Sub?

7. Pub/Sub in Drupal
Not pure Pub / Sub
Content synchronization (tightly coupled)
Content propagation (loosely coupled)
Domain module alternative
A hybrid system (topic and content based)
The content are nodes
Supports Pull and Push
Uses XML-RPC

8. Pub/Sub in Drupal
Topics are defined by views
Content filtering is done via filters
node_save() and alternatives
Supports private channels
Token based security
Works with most CCK field types (no userreference)
Syncs taxonomy terms
Syncs files uploaded to nodes
Deletion propagation

9. Basic usage - Demo
Set up taxonomies
Set up a publisher and a channel
Set up a subscriber to that channel
Add some nodes into the queue
Push
Pull

10. Advanced usage - Demo
Using the filters
Node reference
Deletion propagation
Syncing uploaded files
Excluding nodes
Tying nodes together

11. Integration
hook_publish_prepare(&$node)
publish_node_was_changed($nid)
hook_subscribe_presave(&$node)
hook_subscribe_postsave(&$node)

12. Integration
hook_publish_prepare(&$node)
function flag_pub_sub_publish_prepare(&$node) {
$flag = flag_get_flag(FLAG_PUB_SUB_FLAG_NAME);
if ($flag == null) {
return;
}
if (!$flag->is_flagged($node->nid)) {
return;
}
$node->flag_pub_sub = array(
FLAG_PUB_SUB_FLAG_NAME => true,
);
}

13. Integration
hook_subscribe_postsave(&$node)
function flag_pub_sub_subscribe_postsave(&$node) {
$flag = flag_get_flag(FLAG_PUB_SUB_FLAG_NAME);
if ($flag == null) {
return;
}
if ($node->flag_pub_sub[FLAG_PUB_SUB_FLAG_NAME]) {
$flag->flag('flag', $node->nid);
}
}

14. Integration
publish_node_was_changed($nid)
_bulk_media_update_statistics($nid);
if (module_exists('publish')) {
publish_node_was_changed($nid);
}

15. Case study:
Urbo.ro
‣We use Pub / Sub to sync nodes
‣Custom modules for extra data
‣21 channels and subscriptions
‣57 k nodes managed

16. Thanks
andu@ctrlz.ro
http://ctrlz.ro / http://corporate.adulmec.ro
Photo credit: Flickr users Gl3am, nidhug and scattered sunshine.