Mutual Exclusive Cases

In this example, we are going to see how we can create a Parallel with mutually exclusive branches.

This example is the same as the multiple branches example except that we are now going to rely on the Knative switch function to provide a soft mutual exclusivity guarantee.

NOTE: this example must be deployed in the default namespace.

Prerequisites

Please refer to the sample overview for the prerequisites.

Create the Knative Services

Let’s first create the switcher and transformer services that we will use in our Parallel.

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: me-even-odd-switcher
spec:
  template:
    spec:
      containers:
      - image: villardl/switcher-nodejs:0.1
        env:
        - name: EXPRESSION
          value: Math.round(Date.parse(event.time) / 60000) % 2
        - name: CASES
          value: '[0, 1]'
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: even-transformer
spec:
  template:
    spec:
      containers:
      - image: villardl/transformer-nodejs:0.1
        env:
        - name: TRANSFORMER
          value: |
            ({"message": "we are even!"})
---
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: odd-transformer
spec:
  template:
    spec:
      containers:
      - image: villardl/transformer-nodejs:0.1
        env:
        - name: TRANSFORMER
          value: |
            ({"message": "this is odd!"})
.

kubectl create -f ./switcher.yaml -f ./transformers.yaml

Create the Service displaying the events created by Parallel

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

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

Create the Parallel object

The parallel.yaml file contains the specifications for creating the Parallel object.

apiVersion: flows.knative.dev/v1
kind: Parallel
metadata:
  name: me-odd-even-parallel
spec:
  channelTemplate:
    apiVersion: messaging.knative.dev/v1
    kind: InMemoryChannel
  branches:
    - filter:
        uri: "http://me-even-odd-switcher.default.svc.cluster.local/0"
      subscriber:
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: me-even-transformer
    - filter:
        uri: "http://me-even-odd-switcher.default.svc.cluster.local/1"
      subscriber:
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: me-odd-transformer
  reply:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: me-event-display

kubectl create -f ./parallel.yaml

Create the PingSource targeting the Parallel object

This will create a PingSource which will send a CloudEvent with {"message": "Even or odd?"} as the data payload every minute.

apiVersion: sources.knative.dev/v1beta2
kind: PingSource
metadata:
  name: me-ping-source
spec:
  schedule: "*/1 * * * *"
  contentType: "application/json"
  data: '{"message": "Even or odd?"}'
  sink:
    ref:
      apiVersion: flows.knative.dev/v1
      kind: Parallel
      name: me-odd-even-parallel

kubectl create -f ./ping-source.yaml

Inspecting the results

You can now see the final output by inspecting the logs of the me-event-display pods. Note that since we set the PingSource to emit every minute, it might take some time for the events to show up in the logs.

Let’s look at the me-event-display log:

kubectl logs -l serving.knative.dev/service=me-event-display --tail=50 -c user-container
☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/me-ping-source
  id: 0b0db15c-9b36-4388-8eaa-8c23a9dc2707
  time: 2020-03-03T21:30:00.0007292Z
  datacontenttype: application/json; charset=utf-8
Extensions,
  knativehistory: me-odd-even-parallel-kn-parallel-kn-channel.default.svc.cluster.local; me-odd-even-parallel-kn-parallel-0-kn-channel.default.svc.cluster.local
  traceparent: 00-e8b17109cd21d4fa66a86633b5a614c7-ba96d220fe13211c-00
Data,
  {
    "message": "we are even!"
  }
☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/me-ping-source
  id: 321170d1-dea7-4b18-9290-28adb1de089b
  time: 2020-03-03T21:31:00.0007847Z
  datacontenttype: application/json; charset=utf-8
Extensions,
  knativehistory: me-odd-even-parallel-kn-parallel-kn-channel.default.svc.cluster.local; me-odd-even-parallel-kn-parallel-1-kn-channel.default.svc.cluster.local
  traceparent: 00-78d8b044d23c85789f0a13fd3679ac24-1d69ddde56d620c7-00
Data,
  {
    "message": "this is odd!"
  }