NATS¶

NATS event-source listens to NATS subject notifications and helps sensor trigger the workloads.

Event Structure¶

The structure of an event dispatched by the event-source over the eventbus looks like following,

    {
        "context": {
          "type": "type_of_event_source",
          "specversion": "cloud_events_version",
          "source": "name_of_the_event_source",
          "id": "unique_event_id",
          "time": "event_time",
          "datacontenttype": "type_of_data",
          "subject": "name_of_the_configuration_within_event_source"
        },
        "data": {
          "subject": "name_of_the_nats_subject",
          "headers": "headers_of_the_nats_message",
          "body": "message_payload"
        }
    }

Specification¶

NATS event-source specification is available here.

Setup¶

Make sure to have NATS cluster deployed in the Kubernetes. If you don't have one already installed, please refer https://github.com/nats-io/nats-operator for details.

NATS cluster setup for test purposes,

    apiVersion: v1
    kind: Service
    metadata:
      name: nats
      namespace: argo-events
      labels:
        component: nats
    spec:
      selector:
        component: nats
      type: ClusterIP
      ports:
      - name: client
        port: 4222
      - name: cluster
        port: 6222
      - name: monitor
        port: 8222
    ---
    apiVersion: apps/v1beta1
    kind: StatefulSet
    metadata:
      name: nats
      namespace: argo-events
      labels:
        component: nats
    spec:
      serviceName: nats
      replicas: 1
      template:
        metadata:
          labels:
            component: nats
        spec:
          containers:
          - name: nats
            image: nats:latest
            ports:
            - containerPort: 4222
              name: client
            - containerPort: 6222
              name: cluster
            - containerPort: 8222
              name: monitor
            livenessProbe:
              httpGet:
                path: /
                port: 8222
              initialDelaySeconds: 10
              timeoutSeconds: 5

Create the event source by running the following command.

kubectl apply -n argo-events -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/event-sources/nats.yaml

Create the sensor by running the following command.

kubectl apply -n argo-events -f https://raw.githubusercontent.com/argoproj/argo-events/stable/examples/sensors/nats.yaml

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
```
Publish a message for the subject specified in the event source. 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 foo '{"message": "hello"}'
```
Once a message is published, an argo workflow will be triggered. Run argo list to find the workflow.

Troubleshoot¶

Please read the FAQ.