Sequence wired to event-display

We are going to create the following logical configuration. We create a PingSource, feeding events to a Sequence, then taking the output of that Sequence and displaying the resulting output.

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

Prerequisites

For this example, we’ll assume you have set up an InMemoryChannel as well as Knative Serving (for our functions). The examples use default namespace, again, if you want to deploy to another Namespace, you will need to modify the examples to reflect this.

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

Setup

Create the Knative Services

Change default in the following command to create the steps in the namespace where you want resources created:

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"
---

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.

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: Service
      apiVersion: serving.knative.dev/v1
      name: event-display

Change default in the following command to create the Sequence in the namespace where you want the resources to be created:

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

Create the Service displaying the events created by Sequence

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

Change default in the following command to create the Sequence in the namespace where you want your resources to be created:

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

Create the PingSource targeting the Sequence

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: flows.knative.dev/v1
      kind: Sequence
      name: sequence

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

Inspecting the results

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

kubectl -n default get pods

Wait a bit and then look at the logs for the event-display pod:

kubectl -n default logs -l serving.knative.dev/service=event-display -c user-container --tail=-1
☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: samples.http.mode3
  source: /apis/v1/namespaces/default/pingsources/ping-source
  id: e8fa7906-ab62-4e61-9c13-a9406e2130a9
  time: 2020-03-02T20:52:00.0004957Z
  datacontenttype: application/json
Extensions,
  knativehistory: 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
  traceparent: 00-6e2947379387f35ddc933b9190af16ad-de3db0bc4e442394-00
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.