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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-contrib/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!"
}