ACS-PubSub Clustered Node Strategy

Short description

This stategy can be used by Tigase ACS - PubSub component in which each PubSub node is handled on every cluster node but each cluster node will contain only partial information about user connections. This way strategy is better suited for deployments with PubSub nodes having a lot of subscribers. The benefit of using ClusterNodeStrategy in this case is reduced network traffic on cluster connections, as most of notifications and retrieval of items will be handled on the same cluster node to which user is connected.

Description of processing

In this strategy all configuration changes of pubsub nodes within same PubSub service JID are handled on the same node of the cluster (dynamically selected based on hash of service JID and number of connected nodes). After making changes to node configuration every cluster node is notified about this particular node identification (node name as well as service JID to which it belongs) and they refresh it’s cached configuration.

Presences sent from users to PubSub service will be delivered to every node of a cluster.

If every other IQ stanza sent to PubSub service which is does not change configuration of a node and is item publication stanza then this stanza will always be processed on local node (as data retrieval/removal may be done only on one node as items are not cached).

For IQ stanzas which are stanza responsible for publication of an item is forwarded for processing to every cluster node as only in this case PubSub will able to properly send notifications (as notification are generate always on local user node which reduces cluster network traffic).

Rules of processing packets:
  • presence - packets are delivered to every cluster node as each cluster node is responsible for handling different PubSub nodes
  • message - is always processed locally
  • iq - cluster node which will process this packet is selected based on following rules:

    • non-PubSub packets (no pubsub subelement) are processed on local node
    • PubSub related packets without PubSub node name or packets that change PubSub node configuration (and contains node name and one of the following subelements: create, configure, default, delete) are processed on cluster node selected on hashcode derived from to attribute (service JID) and number of cluster nodes (this is done deal with concurrency issues between configuration changes)
    • PubSub item publication packets (must contain node name attribute within pubsub element) are delivered to all cluster nodes and each cluster node generates notifications about item publication to users connected to that particular cluster node.


This strategy will react to PubSub configuration node change and will send notification to every cluster node (as every cluster node is responsible for processing items for every PubSub node) to refresh particular PubSub node configuration.


Result of processing of packets generated on remote node should be filtered if packet was also processed on local node, so if packet from one cluster node was forwarded to other cluster node for processing but was not processed locally, then response packet should be filtered when this PubSub clustering strategy is used.