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.