Kafka Datasource

The Kafka datasource is used with a distributed installation of ALEC. It interfaces with OpenNMS by leveraging the event consumer and Kafka Producer features.

The Kafka Producer forwards alarms, nodes, and network topology data that is encoded in OpenNMS protocol buffers to topics (see Kafka Producer in the main documentation). The datasource consumes data from these topics and uses it to provide ALEC with a feed of alarms and inventory information.

Configure topics

You can update the following properties to configure the names of individual Kafka topics:

Property Description Default Value


Alarms managed by OpenNMS.



Alarm feedback managed by OpenNMS.



Topology managed by OpenNMS.



Node inventory managed by OpenNMS.



Used to forward events to OpenNMS.



Used to maintain inventory state.


These topics must exist in the Kafka broker for the datasource to operate.

Event compatibility

The eventTimeFormat property is used to determine how event creation times are encoded when ALEC sends events to OpenNMS. It should be set to its default value (iso) to ensure that event data is compatible with ALEC.

Scripted extensions

You can modify or extend ALEC’s mapping configuration script by updating or overwriting inventory.groovy. If you choose to overwrite the file, you must update the datasource bundle’s configuration to point to the replacement script on your local file system:

Update scriptFile property in org.opennms.alec.datasource.opennms.kafka
config:edit org.opennms.alec.datasource.opennms.kafka
config:property-set scriptFile /tmp/inventory.groovy
If you replace the script, the replacement must use a scripting engine that implements Invocable, and the file must be UTF-8 encoded.


Three methods are exposed to the InventoryObject script:

Method Description

InventoryObjects edgeToInventory(TopologyEdge edge)

Converts data stored in edge to an edge on the network topology map.

List<InventoryObject> toInventoryObjects(OpennmsModelProtos.Node node)

Converts data stored in node to an inventory object on the network topology map.

EnrichedAlarm enrichAlarm(OpennmsModelProtos.Alarm alarm)

Identifies the InventoryObject to which an alarm is attached.

Because edge and node data is received via Kafka topics, the edgeToInventory and toInventoryObjects are invoked, respectively. They allow ALEC to create and maintain a full list of inventory objects.

When alarms are stored in the Kafka topic, the enrichAlarm method is invoked. It uses enriched alarm data to identify all inventory objects that are affected by an alarm.