NATS Trigger¶

NATS trigger allows sensor to publish events on NATS subjects. This trigger helps source the events from outside world into your messaging queues.

Specification¶

The NATS trigger specification is available here.

Walkthrough¶

Consider a scenario where you are expecting a file drop onto a Minio bucket and want to place that event on a NATS subject.
Set up the Minio Event Source here. Do not create the Minio sensor, we are going to create it in next step.

Lets create the sensor.

apiVersion: argoproj.io/v1alpha1
kind: Sensor
metadata:
  name: minio-sensor
spec:
  dependencies:
    - name: test-dep
      eventSourceName: minio
      eventName: example
  triggers:
    - template:
        name: nats-trigger
        nats:
          # NATS Server URL
          url: nats.argo-events.svc:4222
          # Name of the subject
          subject: minio-events
          payload:
            - src:
                dependencyName: test-dep
                dataKey: notification.0.s3.object.key
              dest: fileName
            - src:
                dependencyName: test-dep
                dataKey: notification.0.s3.bucket.name
              dest: bucket

The NATS message needs a body. In order to construct message based on the event data, sensor offers payload field as a part of the NATS trigger.

The payload contains the list of src which refers to the source event and dest which refers to destination key within result request payload.

The payload declared above will generate a message body like below,
```
 {
     "fileName": "hello.txt" // name/key of the object
     "bucket": "input" // name of the bucket
 }
```
If you are running NATS on local K8s cluster, make sure to port-forward to pod.
```
kubectl -n argo-events port-forward <nats-pod-name> 4222:4222
```
Subscribe to the subject called minio-events. Refer the nats example to publish a message to the subject https://github.com/nats-io/go-nats-examples/tree/master/patterns/publish-subscribe.
```
   go run main.go -s localhost minio-events'
```
Drop a file called hello.txt onto the bucket input and you will receive the message on NATS subscriber as follows.
```
[#1] Received on [minio-events]: '{"bucket":"input","fileName":"hello.txt"}'
```