Creating a Wiretap

In this guide we will create a Wiretap to monitor the CloudEvent traffic happening within our bridge.

What is a Wiretap?

A Wiretap is a powerful debugging tool/methodology that can be used to understand the flow of events through the system by subscribing to all of the events that pass through the associated Broker. This is accomplished by the use of a Trigger to route all of the events into a logging service.

Implementing a Wiretap

Creating an Example Bridge

Lets create a configuration that demonstrates the idea of a wiretap. The full manifest is available here in case you want to directly apply the whole configuration to your cluster.

To start, we need to create a WebhookSource that will receive events over HTTP, and a Broker that will ingest those events:

apiVersion: eventing.triggermesh.io/v1alpha1
kind: MemoryBroker
metadata:
  name: events
---

apiVersion: sources.triggermesh.io/v1alpha1
kind: WebhookSource
metadata:
  name: webhook
spec:
  eventType: webhook.event
  sink:
    ref:
      apiVersion: eventing.triggermesh.io/v1alpha1
      kind: MemoryBroker
      name: events

Implement a Wiretap

To add a Wiretap, we can create a Service and a Trigger. The Service we will be using is called Event Display, which is a simple service that logs the events it receives.

We'll create a Trigger that routes all events passing through the broker to the Event Display service:

apiVersion: apps/v1
kind: Deployment
metadata:
  name: event-display
spec:
  replicas: 1
  selector:
    matchLabels: &labels
      app: event-display
  template:
    metadata:
      labels: *labels
    spec:
      containers:
        - name: event-display
          image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

---

kind: Service
apiVersion: v1
metadata:
  name: event-display
spec:
  selector:
    app: event-display
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080

---

apiVersion: eventing.triggermesh.io/v1alpha1
kind: Trigger
metadata:
  name: event-display
spec:
  broker:
    group: eventing.triggermesh.io
    kind: MemoryBroker
    name: events
  target:
    ref:
      apiVersion: v1
      kind: Service
      name: event-display

Using the Wiretap

Now that we have all the parts in place, we can utilize our Wiretap to monitor the events that are being sent through our broker from the WebhookSource.

Retrieve the URL where the Webhook is listening for incoming requests.

$kubectl get webhooksources.sources.triggermesh.io webhook
NAME      READY   REASON   URL                                                              SINK                                                     AGE
webhook   True             http://webhooksource-webhook.wiretap.127.0.0.1.sslip.io   http://demo-mb-broker.wiretap.svc.cluster.local   4m14s

Use curl or any HTTP capable client to post an event to the webhook.

curl -d '{"message":"test my bridge"}' http://webhooksource-webhook.wiretap.127.0.0.1.sslip.io

View the logs of the Event Display service:

kubectl logs deployments/event-display