OpenShift 4.3 之Knative-Tutorial(6) Eventing之Channel和Subscription

概念

Knative Eventing中的Channel和Subscription類似JMS消息體系中的Topic/Subscribe機制。Event Source是消息的發佈者（類似JMS的Publisher），Channle是傳送消息的通道（類似JMS的Topic），而Subscription通過訂閱Channel獲取到相關的Event，並且使用Knative Serving的服務處理消息。

操作

1. 創建如下內容的channel.yaml文件，其中定義了名爲eventinghello-ch的Channel類型的對象。

apiVersion: messaging.knative.dev/v1alpha1
kind: Channel
metadata:
  name: eventinghello-ch

2. 執行命令生成Channel對象，然後查看eventinghello-ch狀態爲READY=true。

$ oc -n knativetutorial apply -f channel.yaml
 
$ oc -n knativetutorial get channel
NAME               READY   REASON   URL                                                                    AGE
eventinghello-ch   True             http://eventinghello-ch-kn-channel.knativetutorial.svc.cluster.local   34s
 
$ oc -n knativetutorial get svc
NAME                          TYPE           CLUSTER-IP       EXTERNAL-IP                                           PORT(S)      AGE
eventinghello-ch-kn-channel   ExternalName   <none>           imc-dispatcher.knative-eventing.svc.cluster.local     <none>       40s

3. 創建如下內容的event-source.yaml文件，其中定義了名爲my-cjs的CronJobSource類型的對象，它每2秒產生一次事件。事件發送目標Sink爲eventinghello-ch的Channel。

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:
  name: my-cjs
spec:
  schedule: "*/2 * * * *"
  data: '{"message": "From CronJob Source"}'
  sink:
   ref:
    apiVersion: messaging.knative.dev/v1alpha1 
    kind: Channel 
    name: eventinghello-ch

4. 執行命令生成CronJobSource對象，然後查看my-cjs狀態爲READY=true。說明：如果接收事件的目標Sink沒有Ready，那麼my-cjs的狀態也不會Ready。

$ oc -n knativetutorial apply -f event-source.yaml
cronjobsource.sources.eventing.knative.dev/event-greeter-cronjob-source created
 
$ oc -n knativetutorial get cronjobsources
NAME     READY   AGE
my-cjs   True    76s
 
$ oc -n knativetutorial get deployment
NAME                                                        READY   UP-TO-DATE   AVAILABLE   AGE
cronjobsource-my-cjs-bf3f1b8f-fc05-46d0-ae5c-a5bd9c7377b0   1/1     1            1           44m

5. 分別創建eventing-helloa-sink.yaml和eventing-hellob-sink.yaml文件，內容如下。它們分別定義了名爲eventinghelloa和eventinghellob的Service。

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: eventinghelloa
spec:
  template:
    metadata:
      name: eventinghelloa-v1
      annotations:
        autoscaling.knative.dev/target: "1"
    spec:
      containers:
      - image: quay.io/burrsutter/eventinghello:0.0.1

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: eventinghellob
spec:
  template:
    metadata:
      name: eventinghellob-v1
      annotations:
        autoscaling.knative.dev/target: "1"
    spec:
      containers:
      - image: quay.io/burrsutter/eventinghello:0.0.1

6. 執行命令，創建eventinghelloa和eventinghellob服務。然後查看和eventinghelloa和eventinghellob相關的Deployment和Serivce。

$ oc apply -n knativetutorial -f eventing-helloa-sink.yaml
$ oc apply -n knativetutorial -f eventing-hellob-sink.yaml
 
$ oc -n knativetutorial get deployment 
NAME                                                        READY   UP-TO-DATE   AVAILABLE   AGE
cronjobsource-my-cjs-bf3f1b8f-fc05-46d0-ae5c-a5bd9c7377b0   1/1     1            1           44m
eventinghelloa-v1-deployment                                0/0     0            0           24m
eventinghellob-v1-deployment                                0/0     0            0           24m
 
$ oc -n knativetutorial get svc
NAME                          TYPE           CLUSTER-IP       EXTERNAL-IP                                                  PORT(S)                             AGE
eventinghello-ch-kn-channel   ExternalName   <none>           imc-dispatcher.knative-eventing.svc.cluster.local            <none>                              53m
eventinghelloa                ExternalName   <none>           kourier-internal.knative-serving-ingress.svc.cluster.local   <none>                              12s
eventinghelloa-v1             ClusterIP      172.30.177.109   <none>                                                       80/TCP                              22s
eventinghelloa-v1-private     ClusterIP      172.30.210.190   <none>                                                       80/TCP,9090/TCP,9091/TCP,8022/TCP   22s
eventinghellob                ExternalName   <none>           kourier-internal.knative-serving-ingress.svc.cluster.local   <none>                              11s
eventinghellob-v1             ClusterIP      172.30.116.241   <none>                                                       80/TCP                              21s
eventinghellob-v1-private     ClusterIP      172.30.45.121    <none>                                                       80/TCP,9090/TCP,9091/TCP,8022/TCP   21s

7. 創建eventing-helloa-sub.yaml和eventing-hellob-sub.yaml文件，內容分別如下。他們分別定義了名爲eventinghelloa-sub和eventinghellob-sub的Subscription。這兩個Subscription都是從名爲eventinghello-ch的Channel獲取消息，只不過一個用名爲eventinghelloa的Service處理，另一個用名爲eventinghellob的Service處理。

apiVersion: messaging.knative.dev/v1alpha1
kind: Subscription
metadata:
  name: eventinghelloa-sub
spec:
  channel:
    apiVersion: messaging.knative.dev/v1alpha1
    kind: Channel
    name: eventinghello-ch
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: eventinghelloa

apiVersion: messaging.knative.dev/v1alpha1
kind: Subscription
metadata:
  name: eventinghellob-sub
spec:
  channel:
    apiVersion: messaging.knative.dev/v1alpha1
    kind: Channel
    name: eventinghello-ch
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: eventinghellob

8. 執行命令，分別創建名爲eventinghelloa-sub和eventinghellob-sub的Subscription，然後查看它們的狀態變爲READY=True。

$ oc -n knativetutorial apply -f eventing-helloa-sub.yaml
$ oc -n knativetutorial apply -f eventing-hellob-sub.yaml
 
$ oc -n knativetutorial get subscriptions.messaging.knative.dev
NAME                 READY   REASON   AGE
eventinghelloa-sub   True             7m11s
eventinghellob-sub   True             7m11s

9. 在控制檯查看運行情況。可以看到eventinghelloa和eventinghellob的實例數會在0和1之間變化。
   
   
10. 執行命令，清理環境。

oc -n knativetutorial delete -f channel.yaml
oc -n knativetutorial delete -f event-source.yaml
oc -n knativetutorial delete -f eventing-helloa-sink.yaml
oc -n knativetutorial delete -f eventing-hellob-sink.yaml
oc -n knativetutorial delete -f eventing-helloa-sub.yaml
oc -n knativetutorial delete -f eventing-hellob-sub.yaml

參考

• https://github.com/RedHatWorkshops/knative-on-ocp4/blob/master/6.AddingChannelsAndSubscriptions.md