eventing: Runing CronJobSource Problem "53: no such host"

Describe the bug About Knative Eventing v0.9.0， creating the CronJobSource, but got the problem :

{"level":"error","ts":1569760380.0051033,"logger":"fallback","caller":"cronjobevents/adapter.go:113","msg":"failed to send cloudevent{error 25 0  Post http://event-display.default.svc.cluster.local: dial tcp: lookup event-display.default.svc.cluster.local on 172.21.0.10:53: no such host}","stacktrace":"knative.dev/eventing/pkg/adapter/cronjobevents.(*Adapter).cronTick\n\t/home/prow/go/src/knative.dev/eventing/pkg/adapter/cronjobevents/adapter.go:113\nknative.dev/eventing/vendor/github.com/robfig/cron.FuncJob.Run\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:92\nknative.dev/eventing/vendor/github.com/robfig/cron.(*Cron).runWithRecovery\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:165"}

Expected behavior Send the message to the event-display

To Reproduce Create the CronJobSource:

apiVersion: sources.eventing.knative.dev/v1alpha1
kind: CronJobSource
metadata:
  name: test-cronjob
spec:
  schedule: "*/1 * * * *"
  data: '{"message": "sync"}'
  sink:
    apiVersion: serving.knative.dev/v1alpha1
    kind: Service
    name: event-display

And the event-display:

apiVersion: serving.knative.dev/v1alpha1
kind: Service
metadata:
  name: event-display
  namespace: default
spec:
  template:
    spec:
      containers:
      - # This corresponds to
        # https://github.com/knative/eventing-contrib/blob/release-0.5/cmd/event_display/main.go
        image: gcr.io/knative-releases/github.com/knative/eventing-sources/cmd/event_display@sha256:bf45b3eb1e7fc4cb63d6a5a6416cf696295484a7662e0cf9ccdf5c080542c21d

Error Output:

$ kubectl logs cronjobsource-test-cronjob-9314365a-e2b0-11e9-a78e-2ef5695pjjbx

{"level":"error","ts":1569760620.0037365,"logger":"fallback","caller":"cronjobevents/adapter.go:113","msg":"failed to send cloudevent{error 25 0  Post http://event-display.default.svc.cluster.local: dial tcp: lookup event-display.default.svc.cluster.local on 172.21.0.10:53: no such host}","stacktrace":"knative.dev/eventing/pkg/adapter/cronjobevents.(*Adapter).cronTick\n\t/home/prow/go/src/knative.dev/eventing/pkg/adapter/cronjobevents/adapter.go:113\nknative.dev/eventing/vendor/github.com/robfig/cron.FuncJob.Run\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:92\nknative.dev/eventing/vendor/github.com/robfig/cron.(*Cron).runWithRecovery\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:165"}
{"level":"error","ts":1569760680.0039418,"logger":"fallback","caller":"cronjobevents/adapter.go:113","msg":"failed to send cloudevent{error 25 0  Post http://event-display.default.svc.cluster.local: dial tcp: lookup event-display.default.svc.cluster.local on 172.21.0.10:53: no such host}","stacktrace":"knative.dev/eventing/pkg/adapter/cronjobevents.(*Adapter).cronTick\n\t/home/prow/go/src/knative.dev/eventing/pkg/adapter/cronjobevents/adapter.go:113\nknative.dev/eventing/vendor/github.com/robfig/cron.FuncJob.Run\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:92\nknative.dev/eventing/vendor/github.com/robfig/cron.(*Cron).runWithRecovery\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:165"}
{"level":"error","ts":1569760740.0035992,"logger":"fallback","caller":"cronjobevents/adapter.go:113","msg":"failed to send cloudevent{error 25 0  Post http://event-display.default.svc.cluster.local: dial tcp: lookup event-display.default.svc.cluster.local on 172.21.0.10:53: no such host}","stacktrace":"knative.dev/eventing/pkg/adapter/cronjobevents.(*Adapter).cronTick\n\t/home/prow/go/src/knative.dev/eventing/pkg/adapter/cronjobevents/adapter.go:113\nknative.dev/eventing/vendor/github.com/robfig/cron.FuncJob.Run\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:92\nknative.dev/eventing/vendor/github.com/robfig/cron.(*Cron).runWithRecovery\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:165"}
{"level":"error","ts":1569760800.0040033,"logger":"fallback","caller":"cronjobevents/adapter.go:113","msg":"failed to send cloudevent{error 25 0  Post http://event-display.default.svc.cluster.local: dial tcp: lookup event-display.default.svc.cluster.local on 172.21.0.10:53: no such host}","stacktrace":"knative.dev/eventing/pkg/adapter/cronjobevents.(*Adapter).cronTick\n\t/home/prow/go/src/knative.dev/eventing/pkg/adapter/cronjobevents/adapter.go:113\nknative.dev/eventing/vendor/github.com/robfig/cron.FuncJob.Run\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:92\nknative.dev/eventing/vendor/github.com/robfig/cron.(*Cron).runWithRecovery\n\t/home/prow/go/src/knative.dev/eventing/vendor/github.com/robfig/cron/cron.go:165"}

Knative release version v0.9.0

Additional context event-display service is running normally:

[root@iZ8vb67td1x5m1dnct3ki3Z ~]# kubectl get ksvc
NAME            URL                                        LATESTCREATED         LATESTREADY           READY   REASON
event-display   http://event-display.default.example.com   event-display-qjxbr   event-display-qjxbr   True