Clustering

Several Liberators can be configured into a cluster.

A cluster enables a group of Liberators to act as one, in order to monitor licence use and the numbers of users logged on. Client applications can also publish data to a cluster, for example when using the chat facility, so the data’s available to other clients that use Liberators in the cluster.

You can configure the cluster to use a global cache, which means that when a Liberator failover occurs, the Liberator instance that takes over can supply the clients it has taken on with data from the global cache - it doesn’t have to re-request the data from the Integration Adapter or other DataSource application that supplies the data.

Cluster heartbeats

The Liberators forming a cluster exchange heartbeat messages at regular intervals, allowing each of them to check that all the others are still present. If a Liberator’s cluster heartbeat times out, it waits a configurable time and then disconnects from the cluster and tries to reconnect to it. For more about this, see cluster-heartbeat-time and cluster-heartbeat-slack-time in Liberator Clustering configuration

Intelligent Source Routing

You can configure the cluster’s Liberators so that each Liberator subscribes to particular data from the same Integration Adapter or Transformer instance. This feature is called Intelligent Source Routing. It minimises the load on the DataSource peers supplying data to the Liberators, as the peers don’t all serve up data for the same subjects. It also minimises the bandwidth used on the network connecting the Liberators to the Integration Adapters or Transformers, because each update for a particular subscription is only sent by a single Adapter/Transformer; this can be a significant advantage if the DataSource peers are connected to the Liberators over a WAN.

As an example, you could use Intelligent Source Routing when a Transformer performs a particular calculation on some data. All the Liberators in the cluster would direct requests for the data only to the Transformer instance that does the calculation.

You enable Intelligent Source Routing by specifying the Liberator configuration item cluster-cache-source-routing.

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