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Complex Delivery with reply

In Complex Delivery example, we see how an Event Source can fan out a message multiple Services with a Channel and Subscriptions. A Service can also reply to an event with another event. This reply can further be routed to another Service with a Channel and a Subscription:

Complex Delivery with Reply

Channels

Define two InMemoryChannels with channel1.yaml and channel2.yaml:

Create the channels:

kubectl apply -f channel1.yaml -f channel2.yaml

inmemorychannel.messaging.knative.dev/channel1 created
inmemorychannel.messaging.knative.dev/channel2 created

Source

Create a PingSource to target the first channel.

Define source.yaml.

Create the source:

kubectl apply -f source.yaml

cronjobsource.sources.eventing.knative.dev/source created

Services

Create Knative services that will subscribe to the first channel.

Define service1.yaml.

This simply logs out received messages.

Define another service2.yaml for the second service.

This logs the received message and replies back with another CloudEvent. You can check out the source in event-display-with-reply folder.

Create the services:

kubectl apply -f service1.yaml -f service2.yaml

service.serving.knative.dev/service1 created
service.serving.knative.dev/service2 created

Subscriptions

Connect services to the channel with subscriptions.

Define subscription1.yaml.

Define another subscription2.yaml for the second subscription.

Notice that the reply of the second service is routed to the second channel in subscription2.yaml.

Create the subscriptions:

kubectl apply -f subscription1.yaml -f subscription2.yaml

subscription.messaging.knative.dev/subscription1 created
subscription.messaging.knative.dev/subscription2 created

Handle reply

Finally, let's handle the reply messages from service2 to channel2.

Define service3.yaml for the third service that simply logs out messages.

Define subscription3.yaml that connects service3 to channel2.

Create service and subscription:

kubectl apply -f service3.yaml -f subscription3.yaml

service.serving.knative.dev/service3 created
subscription.messaging.knative.dev/subscription3 created

Verify

Check the running pods:

kubectl get pods

NAME                                                              READY STATUS    RESTARTS   AGE
cronjobsource-source-8653ad6d-2499-4b95-91a7-98fdee8f841d-wh6rk   1/1     Running   0          16m
service1-5mf7x-deployment-6bcdb4df9-pnhc4                         2/2     Running   0          5m19s
service2-fd752-deployment-9d589f7b7-m7r8j                         2/2     Running   0          5m19s
service3-hh6c7-deployment-7455c845cd-2ktr4                        2/2     Running   0          65s

Check the logs of the services.

In service1, you should see messages from the CronJobSource:

kubectl logs service1-5mf7x-deployment-6bcdb4df9-pnhc4 -c user-container

info: event_display.Startup[0]
      Event Display received event: {"message":"Hello world from cron!"}

In service2, you should see messages from the CronJobSource and outgoing replies:

kubectl logs service2-fd752-deployment-9d589f7b7-m7r8j -c user-container

info: event_display_with_reply.Startup[0]
      Received CloudEvent
      Id: 2eac9a1d-6f14-4343-a391-8f0fa504258d
      Source: /apis/v1/namespaces/default/cronjobsources/source
      Type: dev.knative.cronjob.event
      Data: {"message":"Hello world from cron!"}
info: event_display_with_reply.Startup[0]
      Replying with CloudEvent
      Id: a38095ae-7816-46a7-8464-2943e26bf66a
      Source: urn:knative/eventing/samples/hello-world
      Type: dev.knative.samples.hifromknative
      Data: "This is a Knative reply!"

In service3, you should see the replied messages:

kubectl logs service3-hh6c7-deployment-7455c845cd-2ktr4 -c user-container

info: event_display.Startup[0]
      Event Display received event: "This is a Knative reply!"