Added cronjob sample (#647)

* Added cronjob sample

Give a sample about how to configure CronJobSource event.

* default namespace

* Refine the sample

Author: whynowy

eventing/README.md

@@ -226,6 +226,19 @@ FTP server for new files or generate events at a set time interval.
   [ObjectReference](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.12/#objectreference-v1-core)
   A reference to the object that should receive events.
 
+### CronJobSource
+
+The CronJobSource fires events based on given [Cron](https://en.wikipedia.org/wiki/Cron) schedule.
+
+**Spec fields**:
+
+- `schedule` (**required**): `string` A [Cron](https://en.wikipedia.org/wiki/Cron) format string, such as `0 * * * *` or `@hourly`.
+- `data`: `string` Optional data sent to downstream receiver.
+- `serviceAccountName`: `string` The name of the ServiceAccount to run the container as.
+- `sink`:
+  [ObjectReference](https://kubernetes.io/docs/reference/generated/kubernetes-api/v1.12/#objectreference-v1-core)
+  A reference to the object that should receive events.
+
 ## Getting Started
 
 - [Setup Knative Serving](../install/README.md)

eventing/samples/cronjob-source/README.md

@@ -0,0 +1,85 @@
+# Cron Job Source example
+
+Cron Job Source example shows how to configure Cron Job as event source for
+functions.
+
+## Deployment Steps
+
+### Prerequisites
+
+1. Setup [Knative Serving](https://github.com/knative/docs/tree/master/serving).
+1. Setup
+   [Knative Eventing](https://github.com/knative/docs/tree/master/eventing).
+
+### Create a Knative Service
+
+In order to verify `CronJobSource` is working, we will create a simple Knative
+Service that dumps incoming messages to its log.
+
+```yaml
+apiVersion: serving.knative.dev/v1alpha1
+kind: Service
+metadata:
+  name: message-dumper
+spec:
+  runLatest:
+    configuration:
+      revisionTemplate:
+        spec:
+          container:
+            image: github.com/knative/eventing-sources/cmd/message_dumper
+```
+
+Use following command to create the service from `service.yaml`:
+
+```shell
+kubectl apply -f service.yaml
+```
+
+### Create Cron Job Event Source
+
+For each set of cron events you want to request, you need to create an Event
+Source in the same namespace as the destiantion. If you need a different
+ServiceAccount to create the Deployment, modify the entry accordingly in the
+yaml.
+
+```yaml
+apiVersion: sources.eventing.knative.dev/v1alpha1
+kind: CronJobSource
+metadata:
+  name: test-cronjob-source
+spec:
+  schedule: "*/2 * * * *"
+  data: '{"message": "Hello world!"}'
+  sink:
+    apiVersion: serving.knative.dev/v1alpha1
+    kind: Service
+    name: message-dumper
+```
+
+Use following command to create the event source from `cronjob-source.yaml`:
+
+```shell
+kubectl apply -f cronjob-source.yaml
+```
+
+### Verify
+
+We will verify that the message was sent to the Knative eventing system by
+looking at message dumper logs.
+
+1. Use [`kail`](https://github.com/boz/kail) to tail the logs of the subscriber.
+
+   ```shell
+   kail -d message-dumper -c user-container --since=10m
+   ```
+
+You should see log lines similar to:
+
+```json
+{
+  "ID": "1543616460000180552-203",
+  "EventTime": "2018-11-30T22:21:00.000186721Z",
+  "Body": "{\"message\": \"Hello world!\"}"
+}
+```

eventing/samples/cronjob-source/cronjob-source.yaml

@@ -0,0 +1,11 @@
+apiVersion: sources.eventing.knative.dev/v1alpha1
+kind: CronJobSource
+metadata:
+  name: test-cronjob-source
+spec:
+  schedule: "*/2 * * * *"
+  data: '{"message": "Hello world!"}'
+  sink:
+    apiVersion: serving.knative.dev/v1alpha1
+    kind: Service
+    name: message-dumper

eventing/samples/cronjob-source/service.yaml

@@ -0,0 +1,13 @@
+# This is a very simple Knative Service that writes the input request to its log.
+
+apiVersion: serving.knative.dev/v1alpha1
+kind: Service
+metadata:
+  name: message-dumper
+spec:
+  runLatest:
+    configuration:
+      revisionTemplate:
+        spec:
+          container:
+            image: github.com/knative/eventing-sources/cmd/message_dumper