Inbound NATS Connector Template

!!! Work in progress !!!

A starting point to build a Start and Intermediate Inbound NATS Connector. Send messages to topics on NATS and have process instances start or catch intermediate events. Feedback and PRs are welcome! In the Connector you'll need to provide the URL of the NATS server, the topic to listen to, and the long polling interval in seconds.

There are three outputs and can be accessed from the event object: event.url, event.topic, event.message

In most cases you'll be interested in event.message. If the message is sent in a JSON string you'll be able to access data within the object using dot notation.

For intermediate catch events you need to set a correlation key in the process using a variable and send the correlation key in the payload as part of the incoming message

Build

You can package the Connector by running the following command:

mvn clean package

This will create the following artifacts:

A thin JAR without dependencies.
An uber JAR containing all dependencies, potentially shaded to avoid classpath conflicts. This will not include the SDK artifacts since those are in scope provided and will be brought along by the respective Connector Runtime executing the Connector.

Shading dependencies

You can use the maven-shade-plugin defined in the Maven configuration to relocate common dependencies that are used in other Connectors and the Connector Runtime. This helps to avoid classpath conflicts when the Connector is executed.

Use the relocations configuration in the Maven Shade plugin to define the dependencies that should be shaded. The Maven Shade documentation provides more details on relocations.

API

Connector Properties

This Connector can be configured with the following properties:

Name	Description	Example
NATS URL	URL of NATS Server	`localhost:4222`
Topic	Topic on NATS Server to monitor	`sampleTopic`
Polling interval	Long polling interval in seconds	`60`
Correlation key (process) - for intermediate catch event	Process variable to correlate incoming message	`processCorrelationKey`
Correlation key (payload) - for intermediate catch event	Correlation key in incoming message	`event.message.messageCorrelationKey`
Activation condition - for intermediate catch event	Condition under which the Connector triggers	`event.message.aVariable = 'ok'`

Output

This Connector produces the following output:

{
  "event": {
    "url": "localhost:4222",
    "topic": "sampleTopic",
    "message": "some message"
  }
}

Test locally

Run unit tests

mvn clean verify

Test with local runtime

Use the Camunda Connector Runtime to run your function as a local Java application.

In your IDE you can also simply navigate to the LocalContainerRuntime class in test scope and run it via your IDE. If necessary, you can adjust application.properties in test scope.

Element Template

The element templates can be found in the element-templates/inbound-template-connector.json file.

camunda-community-hub / camunda-8-inbound-connector-nats