Getting Started with Eventing

Use this guide to learn how to create, send, and verify events in Knative. The steps in this guide demonstrate a basic developer flow for managing events in Knative, including:

Installing the Knative Eventing component
Creating and configuring Knative Eventing Resources
Sending events with HTTP requests
Verifying events were sent correctly

Before you begin

To complete this guide, you will need the following installed and running:

A Kubernetes cluster running v1.16 or higher.
kubectl CLI tool within a minor version of your Kubernetes cluster.
curl v7.65 or higher.
Knative Eventing component.

Important Note: Some Knative Eventing features do not work when using Minikube due to this bug. For local testing you can use kind.

Installing Knative Eventing

Install the Knative Eventing.

Setting up Knative Eventing Resources

Before you start to manage events, you need to create the objects needed to transport the events.

Creating and configuring an Eventing namespace

In this section you create the event-example namespace and add a Broker to that namespace. You use namespaces to group together and organize your Knative resources, including the Eventing subcomponents.

Run the following command to create a namespace called event-example:
```
kubectl create namespace event-example
```
This creates an empty namespace called event-example.
Add a Broker named default to your namespace with the following command:
```
kubectl create -f - <<EOF
apiVersion: eventing.knative.dev/v1
kind: Broker
metadata:
  name: default
  namespace: event-example
EOF
```
This creates the default Broker for the namespace based on config. The Broker is a resource that will allow you to manage your events.

In the next section, you will need to verify that the resources you added in this section are running correctly. Then, you can create the rest of the eventing resources you need to manage events.

Optional Sugar Controller

When installed, the Sugar Controller for Knative Eventing will add a controller that reacts to special labels and annotations for your resources, you can skip manually creating a Broker in the above step and instead label a namespace:

kubectl label namespace event-example eventing.knative.dev/injection=enabled

This gives the event-example namespace the eventing.knative.dev/injection label, which adds resources that will allow you to manage your events.

Validating that the `Broker` is running

The Broker ensures that every event sent by event producers arrives at the correct event consumers. The Broker was created when you labeled your namespace as ready for eventing, but it is important to verify that your Broker is working correctly. In this guide, you will use the default broker.

Run the following command to verify that the Broker is in a healthy state:

kubectl --namespace event-example get Broker default

This shows the Broker that you created:

NAME      READY   REASON   URL                                                        AGE
default   True             http://default-broker.event-example.svc.cluster.local      1m

When the Broker has the READY=True state, it can begin to manage any events it receives.

If READY=False, wait 2 minutes and re-run the command. If you continue to receive the READY=False, see the Debugging Guide to help troubleshoot the issue.

Now that your Broker is ready to manage events, you can create and configure your event producers and consumers.

Creating event consumers

Your event consumers receive the events sent by event producers. In this step, you will create two event consumers, hello-display and goodbye-display, to demonstrate how you can configure your event producers to selectively target a specific consumer.

To deploy the hello-display consumer to your cluster, run the following command:

kubectl --namespace event-example apply --filename - << END
apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-display
spec:
  replicas: 1
  selector:
    matchLabels: &labels
      app: hello-display
  template:
    metadata:
      labels: *labels
    spec:
      containers:
        - name: event-display
          # Source code: https://github.com/knative/eventing-contrib/tree/master/cmd/event_display
          image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display

---

# Service pointing at the previous Deployment. This will be the target for event
# consumption.
  kind: Service
  apiVersion: v1
  metadata:
    name: hello-display
  spec:
    selector:
      app: hello-display
    ports:
    - protocol: TCP
      port: 80
      targetPort: 8080
END

To deploy the goodbye-display consumer to your cluster, run the following command:

kubectl --namespace event-example apply --filename - << END
apiVersion: apps/v1
kind: Deployment
metadata:
  name: goodbye-display
spec:
  replicas: 1
  selector:
    matchLabels: &labels
      app: goodbye-display
  template:
    metadata:
      labels: *labels
    spec:
      containers:
        - name: event-display
          # Source code: https://github.com/knative/eventing-contrib/tree/master/cmd/event_display
          image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display

---

# Service pointing at the previous Deployment. This will be the target for event
# consumption.
kind: Service
apiVersion: v1
metadata:
  name: goodbye-display
spec:
  selector:
    app: goodbye-display
  ports:
  - protocol: TCP
    port: 80
    targetPort: 8080
END

Just like you did with the Broker, verify that your event consumers are working by running the following command:
```
kubectl --namespace event-example get deployments hello-display goodbye-display
```
This lists the hello-display and goodbye-display consumers that you deployed:
```
NAME              READY   UP-TO-DATE   AVAILABLE   AGE
hello-display     1/1     1            1           26s
goodbye-display   1/1     1            1           16s
```
The number of replicas in your READY column should match the number of replicas in your AVAILABLE column, which might take a few minutes. If after two minutes the numbers do not match, then see the Debugging Guide to help troubleshoot the issue.

Creating `Triggers`

A Trigger defines the events that you want each of your event consumers to receive. Your Broker uses triggers to forward events to the right consumers. Each trigger can specify a filter to select relevant events based on the Cloud Event context attributes.

To create the first Trigger, run the following command:

kubectl --namespace event-example apply --filename - << END
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: hello-display
spec:
  broker: default
  filter:
    attributes:
      type: greeting
  subscriber:
    ref:
     apiVersion: v1
     kind: Service
     name: hello-display
END

The command creates a trigger that sends all events of type greeting to your event consumer named hello-display.

To add the second Trigger, run the following command:

kubectl --namespace event-example apply --filename - << END
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: goodbye-display
spec:
  broker: default
  filter:
    attributes:
      source: sendoff
  subscriber:
    ref:
     apiVersion: v1
     kind: Service
     name: goodbye-display
END

The command creates a trigger that sends all events of source sendoff to your event consumer named goodbye-display.

Verify that the triggers are working correctly by running the following command:
```
kubectl --namespace event-example get triggers
```
This returns the hello-display and goodbye-display triggers that you created:
```
NAME                   READY   REASON   BROKER    SUBSCRIBER_URI                                                                 AGE
goodbye-display        True             default   http://goodbye-display.event-example.svc.cluster.local/                        9s
hello-display          True             default   http://hello-display.event-example.svc.cluster.local/                          16s
```
If the triggers are correctly configured, they will be ready and pointing to the correct Broker (the default broker) and SUBSCRIBER_URI has a value similar to (triggerName.namespaceName.svc.cluster.local) exact value dependent on Broker implementation. If this is not the case, see the Debugging Guide to help troubleshoot the issue.

You have now created all of the resources needed to receive and manage events. You created the Broker, which manages the events sent to event consumers with the help of triggers. In the next section, you will make the event producer that will be used to create your events.

Creating event producers

In this section you will create an event producer that you can use to interact with the Knative Eventing subcomponents you created earlier. Most events are created systematically, but this guide uses curl to manually send individual events and demonstrate how these events are received by the correct event consumer. Because you can only access the Broker from within your Eventing cluster, you must create a Pod within that cluster to act as your event producer.

In the following step, you will create a Pod that executes your curl commands to send events to the Broker in your Eventing cluster.

To create the Pod, run the following command:

kubectl --namespace event-example apply --filename - << END
apiVersion: v1
kind: Pod
metadata:
  labels:
    run: curl
  name: curl
spec:
  containers:
    # This could be any image that we can SSH into and has curl.
  - image: radial/busyboxplus:curl
    imagePullPolicy: IfNotPresent
    name: curl
    resources: {}
    stdin: true
    terminationMessagePath: /dev/termination-log
    terminationMessagePolicy: File
    tty: true
END

Now that you’ve set up your Eventing cluster to send and consume events, you will use HTTP requests to manually send separate events and demonstrate how each of those events can target your individual event consumers in the next section.

Sending Events to the `Broker`

Now that you’ve created the Pod, you can create an event by sending an HTTP request to the Broker. SSH into the Pod by running the following command:

  kubectl --namespace event-example attach curl -it

You have sshed into the Pod, and can now make an HTTP request. A prompt similar to the one below will appear:

    Defaulting container name to curl.
    Use 'kubectl describe pod/ -n event-example' to see all of the containers in this pod.
    If you don't see a command prompt, try pressing enter.
    [ root@curl:/ ]$

To show the various types of events you can send, you will make three requests:

To make the first request, which creates an event that has the type greeting, run the following in the SSH terminal:

curl -v "http://default-broker.event-example.svc.cluster.local" \
  -X POST \
  -H "Ce-Id: say-hello" \
  -H "Ce-Specversion: 1.0" \
  -H "Ce-Type: greeting" \
  -H "Ce-Source: not-sendoff" \
  -H "Content-Type: application/json" \
  -d '{"msg":"Hello Knative!"}'

When the Broker receives your event, hello-display will activate and send it to the event consumer of the same name.

If the event has been received, you will receive a 202 Accepted response similar to the one below:

< HTTP/1.1 202 Accepted
< Content-Length: 0
< Date: Mon, 12 Aug 2019 19:48:18 GMT

To make the second request, which creates an event that has the source sendoff, run the following in the SSH terminal:

curl -v "http://default-broker.event-example.svc.cluster.local" \
  -X POST \
  -H "Ce-Id: say-goodbye" \
  -H "Ce-Specversion: 1.0" \
  -H "Ce-Type: not-greeting" \
  -H "Ce-Source: sendoff" \
  -H "Content-Type: application/json" \
  -d '{"msg":"Goodbye Knative!"}'

When the Broker receives your event, goodbye-display will activate and send the event to the event consumer of the same name.

If the event has been received, you will receive a 202 Accepted response similar to the one below:

< HTTP/1.1 202 Accepted
< Content-Length: 0
< Date: Mon, 12 Aug 2019 19:48:18 GMT

To make the third request, which creates an event that has the type greeting and thesource sendoff, run the following in the SSH terminal:

curl -v "http://default-broker.event-example.svc.cluster.local" \
  -X POST \
  -H "Ce-Id: say-hello-goodbye" \
  -H "Ce-Specversion: 1.0" \
  -H "Ce-Type: greeting" \
  -H "Ce-Source: sendoff" \
  -H "Content-Type: application/json" \
  -d '{"msg":"Hello Knative! Goodbye Knative!"}'

When the Broker receives your event, hello-display and goodbye-display will activate and send the event to the event consumer of the same name.

If the event has been received, you will receive a 202 Accepted response similar to the one below:

< HTTP/1.1 202 Accepted
< Content-Length: 0
< Date: Mon, 12 Aug 2019 19:48:18 GMT

Exit SSH by typing exit into the command prompt.

You have sent two events to the hello-display event consumer and two events to the goodbye-display event consumer (note that say-hello-goodbye activates the trigger conditions for both hello-display and goodbye-display). You will verify that these events were received correctly in the next section.

Verifying events were received

After sending events, verify that your events were received by the appropriate Subscribers.

Look at the logs for the hello-display event consumer by running the following command:

kubectl --namespace event-example logs -l app=hello-display --tail=100

This returns the Attributes and Data of the events you sent to hello-display:

☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: greeting
  source: not-sendoff
  id: say-hello
  time: 2019-05-20T17:59:43.81718488Z
  contenttype: application/json
Extensions,
  knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local
Data,
  {
    "msg": "Hello Knative!"
  }
☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: greeting
  source: sendoff
  id: say-hello-goodbye
  time: 2019-05-20T17:59:54.211866425Z
  contenttype: application/json
Extensions,
  knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local
Data,
 {
   "msg": "Hello Knative! Goodbye Knative!"
 }

Look at the logs for the goodbye-display event consumer by running the following command:

kubectl --namespace event-example logs -l app=goodbye-display --tail=100

This returns the Attributes and Data of the events you sent to goodbye-display:

☁️  cloudevents.Event
Validation: valid
Context Attributes,
   specversion: 1.0
   type: not-greeting
   source: sendoff
   id: say-goodbye
   time: 2019-05-20T17:59:49.044926148Z
   contenttype: application/json
 Extensions,
   knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local
Data,
   {
     "msg": "Goodbye Knative!"
   }
 ☁️  cloudevents.Event
 Validation: valid
 Context Attributes,
   specversion: 1.0
   type: greeting
   source: sendoff
   id: say-hello-goodbye
   time: 2019-05-20T17:59:54.211866425Z
   contenttype: application/json
 Extensions,
   knativehistory: default-broker-srk54-channel-24gls.event-example.svc.cluster.local
 Data,
  {
    "msg": "Hello Knative! Goodbye Knative!"
  }

Cleaning up

After you finish this guide, delete your namespace to conserve resources if you do not plan to use them.

Note: If you plan to continue learning about Knative Eventing with one of our code samples, check the requirements of the sample and make sure you do not need a namespace before you delete event-example. You can always reuse your namespaces.

Run the following command to delete event-example:

kubectl delete namespace event-example

This removes the namespace and all of its resources from your cluster.

What’s next

You’ve learned the basics of the Knative Eventing workflow. Here are some additional resources to help you continue to build with the Knative Eventing component.

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Getting Started with Eventing

Before you begin

Installing Knative Eventing

Setting up Knative Eventing Resources

Creating and configuring an Eventing namespace

Optional Sugar Controller

Validating that the Broker is running

Creating event consumers

Creating Triggers

Creating event producers

Sending Events to the Broker

Verifying events were received

Cleaning up

What’s next

Feedback

Validating that the `Broker` is running

Creating `Triggers`

Sending Events to the `Broker`