Using Sequence with Broker and Trigger

We are going to create the following logical configuration. We create a PingSource, feeding events into the Broker, then we create a Filter that wires those events into a Sequence consisting of 3 steps. Then we take the end of the Sequence and feed newly minted events back into the Broker and create another Trigger which will then display those events.

Prerequisites

• Knative Serving
• InMemoryChannel

Note

The examples use the default namespace.

If you want to use different type of Channel, you will have to modify the Sequence.Spec.ChannelTemplate to create the appropriate Channel resources.

The functions used in these examples live in https://github.com/knative/eventing/blob/main/cmd/appender/main.go.

Setup

Creating the Broker

1. To create the cluster default Broker type, copy the following YAML into a file:

   apiVersion: eventing.knative.dev/v1
   kind: Broker
   metadata:
    name: default

2. Apply the YAML file by running the command:

   kubectl apply -f <filename>.yaml

   Where <filename> is the name of the file you created in the previous step.

Create the Knative Services

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: first
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/appender
          env:
            - name: MESSAGE
              value: " - Handled by 0"
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: second
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/appender
          env:
            - name: MESSAGE
              value: " - Handled by 1"
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: third
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/appender
          env:
            - name: MESSAGE
              value: " - Handled by 2"
            - name: TYPE
              value: "samples.http.mod3"
---

Change default in the following command to create the services in the namespace where you have configured your broker:

kubectl -n default create -f ./steps.yaml

Create the Sequence

The sequence.yaml file contains the specifications for creating the Sequence. If you are using a different type of Channel, you need to change the spec.channelTemplate to point to your desired Channel.

Also, change the spec.reply.name to point to your Broker

apiVersion: flows.knative.dev/v1
kind: Sequence
metadata:
  name: sequence
spec:
  channelTemplate:
    apiVersion: messaging.knative.dev/v1
    kind: InMemoryChannel
  steps:
    - ref:
        apiVersion: serving.knative.dev/v1
        kind: Service
        name: first
    - ref:
        apiVersion: serving.knative.dev/v1
        kind: Service
        name: second
    - ref:
        apiVersion: serving.knative.dev/v1
        kind: Service
        name: third
  reply:
    ref:
      kind: Broker
      apiVersion: eventing.knative.dev/v1
      name: default

Change default in the following command to create the sequence in the namespace where you have configured your broker:

kubectl -n default create -f ./sequence.yaml

Create the PingSource targeting the Broker

This will create a PingSource which will send a CloudEvent with {“message”: “Hello world!”} as the data payload every 2 minutes.

apiVersion: sources.knative.dev/v1
kind: PingSource
metadata:
  name: ping-source
spec:
  schedule: "*/2 * * * *"
  contentType: "application/json"
  data: '{"message": "Hello world!"}'
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1
      kind: Broker
      name: default

Change default in the following command to create the PingSource in the namespace where you have configured your broker and sequence:

kubectl -n default create -f ./ping-source.yaml

Create the Trigger targeting the Sequence

apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: sequence-trigger
spec:
  broker: default
  filter:
    attributes:
      type: dev.knative.sources.ping
  subscriber:
    ref:
      apiVersion: flows.knative.dev/v1
      kind: Sequence
      name: sequence

Change default in the following command to create the trigger in the namespace where you have configured your broker and sequence:

kubectl -n default create -f ./trigger.yaml

Create the Service and Trigger displaying the events created by Sequence

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: sequence-display
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display
---
apiVersion: eventing.knative.dev/v1
kind: Trigger
metadata:
  name: display-trigger
spec:
  broker: default
  filter:
    attributes:
      type: samples.http.mod3
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: sequence-display
---

Change default in the following command to create the service and trigger in the namespace where you have configured your broker:

kubectl -n default create -f ./display-trigger.yaml

Inspecting the results

You can now see the final output by inspecting the logs of the sequence-display pods.

kubectl -n default get pods

View the logs for the sequence-display pod:

kubectl -n default logs -l serving.knative.dev/service=sequence-display -c user-container --tail=-1
☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: samples.http.mod3
  source: /apis/v1/namespaces/default/pingsources/ping-source
  id: 159bba01-054a-4ae7-b7be-d4e7c5f773d2
  time: 2020-03-03T14:56:00.000652027Z
  datacontenttype: application/json
Extensions,
  knativearrivaltime: 2020-03-03T14:56:00.018390608Z
  knativehistory: default-kne-trigger-kn-channel.default.svc.cluster.local; sequence-kn-sequence-0-kn-channel.default.svc.cluster.local; sequence-kn-sequence-1-kn-channel.default.svc.cluster.local; sequence-kn-sequence-2-kn-channel.default.svc.cluster.local; default-kne-trigger-kn-channel.default.svc.cluster.local
  traceparent: 00-e893412106ff417a90a5695e53ffd9cc-5829ae45a14ed462-00
Data,
  {
    "id": 0,
    "message": "Hello world! - Handled by 0 - Handled by 1 - Handled by 2"
  }

And you can see that the initial PingSource message {"Hello World!"} has been appended to it by each of the steps in the Sequence.