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Chapter 11. Event sources

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11.1. Getting started with event sources

An event source is an object that links an event producer with an event sink, or consumer. A sink can be a Knative service, channel, or broker that receives events from an event source.

Currently, OpenShift Serverless supports the following event source types:

ApiServerSource
Connects a sink to the Kubernetes API server.
PingSource
Periodically sends ping events with a constant payload. It can be used as a timer.

Sink binding is also supported, which allows you to connect core Kubernetes resources such as Deployment, Job, or StatefulSet with a sink.

You can create and manage Knative event sources using the Developer perspective in the OpenShift Container Platform web console, the kn CLI, or by applying YAML files.

11.1.1. Prerequisites

  • You must have a current installation of OpenShift Serverless, including Knative Serving and Eventing, in your OpenShift Container Platform cluster. This can be installed by a cluster administrator.

11.1.2. Creating event sources

11.1.3. Additional resources

11.2. Using the Knative CLI to list event sources and event source types

You can use the kn CLI to list and manage available event sources or event source types for use with Knative Eventing.

Currently, kn supports management of the following event source types:

API server source
Connects a sink to the Kubernetes API server by creating an APIServerSource object.
Ping source
Periodically sends ping events with a constant payload. It can be used as a timer, and is created as a PingSource object.

11.2.1. Listing available event source types using the Knative CLI

You can list the available event source types in the terminal by using the following command: 

$ kn source list-types

The default output for this command will look like: 

TYPE              NAME                                            DESCRIPTION
ApiServerSource   apiserversources.sources.knative.dev            Watch and send Kubernetes API events to a sink
PingSource        pingsources.sources.knative.dev                 Periodically send ping events to a sink
SinkBinding       sinkbindings.sources.knative.dev                Binding for connecting a PodSpecable to a sink

It is also possible to list available event source types in YAML format: 

$ kn source list-types -o yaml

11.2.2. Listing available event sources using the Knative CLI

You can list the available event sources in the terminal by using the following command: 

$ kn source list

Example output

NAME   TYPE              RESOURCE                               SINK         READY
a1     ApiServerSource   apiserversources.sources.knative.dev   svc:eshow2   True
b1     SinkBinding       sinkbindings.sources.knative.dev       svc:eshow3   False
p1     PingSource        pingsources.sources.knative.dev        svc:eshow1   True

You can list event sources of a specific type only, by using the --type flag. 

$ kn source list --type PingSource

Example output

NAME   TYPE              RESOURCE                               SINK         READY
p1     PingSource        pingsources.sources.knative.dev        svc:eshow1   True

11.2.3. Next steps

11.3. Using the API server source

An API server source is an event source that can be used to connect an event sink, such as a Knative service, to the Kubernetes API server. An API server source watches for Kubernetes events and forwards them to the Knative Eventing broker.

Note

Both of the following procedures require you to create YAML files.

If you change the names of the YAML files from those used in the examples, you must ensure that you also update the corresponding CLI commands.

11.3.1. Using the API server source with the Knative CLI

This section describes the steps required to create an ApiServerSource object using kn commands.

Prerequisites

  • Knative Serving and Eventing are installed on your cluster.
  • You have created the default broker in the same namespace that the API server source will be installed in.
  • You have the kn CLI installed.

Procedure

  1. Create a service account, role, and role binding for the ApiServerSource object.

    You can do this by creating a file named authentication.yaml and copying the following sample code into it: 

    apiVersion: v1
kind: ServiceAccount
metadata:
  name: events-sa
  namespace: default 1

---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: event-watcher
  namespace: default 2
rules:
  - apiGroups:
      - ""
    resources:
      - events
    verbs:
      - get
      - list
      - watch

---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: k8s-ra-event-watcher
  namespace: default 3
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: event-watcher
subjects:
  - kind: ServiceAccount
    name: events-sa
    namespace: default 4
    1 2 3 4
    Change this namespace to the namespace that you have selected for installing the API server source.
    Note

    If you want to reuse an existing service account with the appropriate permissions, you must modify the authentication.yaml file for that service account.

    Create the service account, role binding and cluster binding: 

    $ oc apply -f authentication.yaml

  2. Create an ApiServerSource object that uses a broker as an event sink: 

    $ kn source apiserver create <event_source_name> --sink broker:<broker_name> --resource "event:v1" --service-account <service_account_name> --mode Resource

  3. Create a Knative service that dumps incoming messages to its log: 

    $ kn service create <service_name> --image quay.io/openshift-knative/knative-eventing-sources-event-display:latest

  4. Create a trigger to filter events from the default broker to the service: 

    $ kn trigger create <trigger_name> --sink svc:<service_name>

  5. Create events by launching a Pod in the default namespace: 

    $ oc create deployment hello-node --image=quay.io/openshift-knative/knative-eventing-sources-event-display

  6. Check that the controller is mapped correctly by inspecting the output generated by the following command: 

    $ kn source apiserver describe testevents

    Example output

    Name:                testevents
Namespace:           default
Annotations:         sources.knative.dev/creator=developer, sources.knative.dev/lastModifier=developer
Age:                 3m
ServiceAccountName:  events-sa
Mode:                Resource
Sink:
  Name:       default
  Namespace:  default
  Kind:       Broker (eventing.knative.dev/v1alpha1)
Resources:
  Kind:        event (v1)
  Controller:  false
Conditions:
  OK TYPE                     AGE REASON
  ++ Ready                     3m
  ++ Deployed                  3m
  ++ SinkProvided              3m
  ++ SufficientPermissions     3m
  ++ EventTypesProvided        3m

Verification steps

You can verify that the Kubernetes events were sent to Knative by looking at the message dumper function logs.

  1. Get the pods: 

    $ oc get pods

  2. View the message dumper function logs for the pods: 

    $ oc logs $(oc get pod -o name | grep event-display) -c user-container

    Example output

    ☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.apiserver.resource.update
  datacontenttype: application/json
  ...
Data,
  {
    "apiVersion": "v1",
    "involvedObject": {
      "apiVersion": "v1",
      "fieldPath": "spec.containers{hello-node}",
      "kind": "Pod",
      "name": "hello-node",
      "namespace": "default",
       .....
    },
    "kind": "Event",
    "message": "Started container",
    "metadata": {
      "name": "hello-node.159d7608e3a3572c",
      "namespace": "default",
      ....
    },
    "reason": "Started",
    ...
  }

11.3.2. Deleting an API server source using the Knative CLI

This section describes the steps used to delete the ApiServerSource object, trigger, service, service account, cluster role, and cluster binding using the kn and oc commands.

Prerequisites

  • You must have the kn CLI installed.

Procedure

  1. Delete the trigger: 

    $ kn trigger delete <trigger_name>

  2. Delete the service: 

    $ kn service delete <service_name>

  3. Delete the API server source: 

    $ kn source apiserver delete <source_name>
  4. Delete the service account, cluster role, and cluster binding: 
$ oc delete -f authentication.yaml

11.3.3. Creating an API server source using YAML files

This guide describes the steps required to create an ApiServerSource object using YAML files.

Prerequisites

  • Knative Serving and Eventing are installed on your cluster.
  • You have created the default broker in the same namespace as the one defined in the ApiServerSource object.

Procedure

  1. To create a service account, role, and role binding for the API server source, create a file named authentication.yaml and copy the following sample code into it: 

    apiVersion: v1
kind: ServiceAccount
metadata:
  name: events-sa
  namespace: default 1

---
apiVersion: rbac.authorization.k8s.io/v1
kind: Role
metadata:
  name: event-watcher
  namespace: default 2
rules:
  - apiGroups:
      - ""
    resources:
      - events
    verbs:
      - get
      - list
      - watch

---
apiVersion: rbac.authorization.k8s.io/v1
kind: RoleBinding
metadata:
  name: k8s-ra-event-watcher
  namespace: default 3
roleRef:
  apiGroup: rbac.authorization.k8s.io
  kind: Role
  name: event-watcher
subjects:
  - kind: ServiceAccount
    name: events-sa
    namespace: default 4
    1 2 3 4
    Change this namespace to the namespace that you have selected for installing the API server source.
    Note

    If you want to re-use an existing service account with the appropriate permissions, you must modify the authentication.yaml for that service account.

    After you have created the authentication.yaml file, apply it: 

    $ oc apply -f authentication.yaml

  2. To create an ApiServerSource object, create a file named k8s-events.yaml and copy the following sample code into it: 

    apiVersion: sources.knative.dev/v1alpha1
kind: ApiServerSource
metadata:
  name: testevents
spec:
  serviceAccountName: events-sa
  mode: Resource
  resources:
    - apiVersion: v1
      kind: Event
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1beta1
      kind: Broker
      name: default

    After you have created the k8s-events.yaml file, apply it: 

    $ oc apply -f k8s-events.yaml

  3. To check that the API server source is set up correctly, create a Knative service that dumps incoming messages to its log.

    Copy the following sample YAML into a file named service.yaml: 

    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
  namespace: default
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/knative-eventing-sources-event-display:v0.13.2

    After you have created the service.yaml file, apply it: 

    $ oc apply -f service.yaml

  4. To create a trigger from the default broker that filters events to the service created in the previous step, create a file named trigger.yaml and copy the following sample code into it: 

    apiVersion: eventing.knative.dev/v1alpha1
kind: Trigger
metadata:
  name: event-display-trigger
  namespace: default
spec:
  subscriber:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

    After you have created the trigger.yaml file, apply it: 

    $ oc apply -f trigger.yaml

  5. To create events, launch a pod in the default namespace: 

    $ oc create deployment hello-node --image=quay.io/openshift-knative/knative-eventing-sources-event-display

  6. To check that the controller is mapped correctly, enter the following command and inspect the output: 

    $ oc get apiserversource.sources.knative.dev testevents -o yaml

    Example output

    apiVersion: sources.knative.dev/v1alpha1
kind: ApiServerSource
metadata:
  annotations:
  creationTimestamp: "2020-04-07T17:24:54Z"
  generation: 1
  name: testevents
  namespace: default
  resourceVersion: "62868"
  selfLink: /apis/sources.knative.dev/v1alpha1/namespaces/default/apiserversources/testevents2
  uid: 1603d863-bb06-4d1c-b371-f580b4db99fa
spec:
  mode: Resource
  resources:
  - apiVersion: v1
    controller: false
    controllerSelector:
      apiVersion: ""
      kind: ""
      name: ""
      uid: ""
    kind: Event
    labelSelector: {}
  serviceAccountName: events-sa
  sink:
    ref:
      apiVersion: eventing.knative.dev/v1beta1
      kind: Broker
      name: default

Verification steps

To verify that the Kubernetes events were sent to Knative, you can look at the message dumper function logs.

  1. Get the pods: 

    $ oc get pods

  2. View the message dumper function logs for the pods: 

    $ oc logs $(oc get pod -o name | grep event-display) -c user-container

    Example output

    ☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.apiserver.resource.update
  datacontenttype: application/json
  ...
Data,
  {
    "apiVersion": "v1",
    "involvedObject": {
      "apiVersion": "v1",
      "fieldPath": "spec.containers{hello-node}",
      "kind": "Pod",
      "name": "hello-node",
      "namespace": "default",
       .....
    },
    "kind": "Event",
    "message": "Started container",
    "metadata": {
      "name": "hello-node.159d7608e3a3572c",
      "namespace": "default",
      ....
    },
    "reason": "Started",
    ...
  }

11.3.4. Deleting the API server source

This section describes how to delete the ApiServerSource object, trigger, service, service account, cluster role, and cluster binding by deleting their YAML files.

Procedure

  1. Delete the trigger: 

    $ oc delete -f trigger.yaml

  2. Delete the service: 

    $ oc delete -f service.yaml

  3. Delete the API server source: 

    $ oc delete -f k8s-events.yaml

  4. Delete the service account, cluster role, and cluster binding: 

    $ oc delete -f authentication.yaml

11.4. Using a ping source

A ping source is used to periodically send ping events with a constant payload to an event consumer. A ping source can be used to schedule sending events, similar to a timer, as shown in the example:

Example ping source

apiVersion: sources.knative.dev/v1alpha2
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *" 1
  jsonData: '{"message": "Hello world!"}' 2
  sink: 3
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

1
The schedule of the event specified using CRON expression.
2
The event message body expressed as a JSON encoded data string.
3
These are the details of the event consumer. In this example, we are using a Knative service named event-display.

11.4.1. Creating a ping source using the Knative CLI

The following sections describe how to create, verify and remove a basic PingSource object using the kn CLI.

Prerequisites

  • You have Knative Serving and Eventing installed.
  • You have the kn CLI installed.

Procedure

  1. To verify that the ping source is working, create a simple Knative service that dumps incoming messages to the service’s logs: 

    $ kn service create event-display \
    --image quay.io/openshift-knative/knative-eventing-sources-event-display:latest

  2. For each set of ping events that you want to request, create a PingSource object in the same namespace as the event consumer: 

    $ kn source ping create test-ping-source \
    --schedule "*/2 * * * *" \
    --data '{"message": "Hello world!"}' \
    --sink svc:event-display

  3. Check that the controller is mapped correctly by entering the following command and inspecting the output: 

    $ kn source ping describe test-ping-source

    Example output

    Name:         test-ping-source
Namespace:    default
Annotations:  sources.knative.dev/creator=developer, sources.knative.dev/lastModifier=developer
Age:          15s
Schedule:     */2 * * * *
Data:         {"message": "Hello world!"}

Sink:
  Name:       event-display
  Namespace:  default
  Resource:   Service (serving.knative.dev/v1)

Conditions:
  OK TYPE                 AGE REASON
  ++ Ready                 8s
  ++ Deployed              8s
  ++ SinkProvided         15s
  ++ ValidSchedule        15s
  ++ EventTypeProvided    15s
  ++ ResourcesCorrect     15s

Verification steps

You can verify that the Kubernetes events were sent to the Knative event sink by looking at the logs of the sink pod.

By default, Knative services terminate their pods if no traffic is received within a 60 second period. The example shown in this guide creates a PingSource object that sends a message every 2 minutes, so each message should be observed in a newly created pod.

  1. Watch for new pods created: 

    $ watch oc get pods

  2. Cancel watching the pods using Ctrl+C, then look at the logs of the created pod: 

    $ oc logs $(oc get pod -o name | grep event-display) -c user-container

    Example output

    ☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/test-ping-source
  id: 99e4f4f6-08ff-4bff-acf1-47f61ded68c9
  time: 2020-04-07T16:16:00.000601161Z
  datacontenttype: application/json
Data,
  {
    "message": "Hello world!"
  }

11.4.1.1. Remove the ping source

  1. Delete the PingSource object: 

    $ kn delete pingsources.sources.knative.dev test-ping-source

  2. Delete the event-display service: 

    $ kn delete service.serving.knative.dev event-display

11.4.2. Creating a ping source using YAML files

The following sections describe how to create, verify and remove a basic ping source using YAML files.

Prerequisites

  • You have Knative Serving and Eventing installed.
Note

The following procedure requires you to create YAML files.

If you change the names of the YAML files from those used in the examples, you must ensure that you also update the corresponding CLI commands.

Procedure

  1. To verify that the ping source is working, create a simple Knative service that dumps incoming messages to the service’s logs.

    1. Copy the example YAML into a file named service.yaml: 

      apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/knative-eventing-sources-event-display:latest

    2. Apply the service.yaml file: 

      $ oc apply --filename service.yaml

  2. For each set of ping events that you want to request, create a PingSource object in the same namespace as the event consumer.

    1. Copy the example YAML into a file named ping-source.yaml: 

      apiVersion: sources.knative.dev/v1alpha2
kind: PingSource
metadata:
  name: test-ping-source
spec:
  schedule: "*/2 * * * *"
  jsonData: '{"message": "Hello world!"}'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

    2. Apply the ping-source.yaml file: 

      $ oc apply --filename ping-source.yaml

  3. Check that the controller is mapped correctly by entering the following command and observing the output: 

    $ oc get pingsource.sources.knative.dev test-ping-source -oyaml

    Example output

    apiVersion: sources.knative.dev/v1alpha2
kind: PingSource
metadata:
  annotations:
    sources.knative.dev/creator: developer
    sources.knative.dev/lastModifier: developer
  creationTimestamp: "2020-04-07T16:11:14Z"
  generation: 1
  name: test-ping-source
  namespace: default
  resourceVersion: "55257"
  selfLink: /apis/sources.knative.dev/v1alpha2/namespaces/default/pingsources/test-ping-source
  uid: 3d80d50b-f8c7-4c1b-99f7-3ec00e0a8164
spec:
  jsonData: '{ value: "hello" }'
  schedule: '*/2 * * * *'
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display
      namespace: default

Verification steps

You can verify that the Kubernetes events were sent to the Knative event sink by looking at the logs of the sink pod.

By default, Knative services terminate their pods if no traffic is received within a 60 second period. The example shown in this guide creates a PingSource object that sends a message every 2 minutes, so each message should be observed in a newly created pod.

  1. Watch for new pods created: 

    $ watch oc get pods

  2. Cancel watching the pods using Ctrl+C, then look at the logs of the created pod: 

    $ oc logs $(oc get pod -o name | grep event-display) -c user-container

    Example output

    ☁️  cloudevents.Event
Validation: valid
Context Attributes,
  specversion: 1.0
  type: dev.knative.sources.ping
  source: /apis/v1/namespaces/default/pingsources/test-ping-source
  id: 042ff529-240e-45ee-b40c-3a908129853e
  time: 2020-04-07T16:22:00.000791674Z
  datacontenttype: application/json
Data,
  {
    "message": "Hello world!"
  }

11.4.2.1. Remove the PingSource

  1. Delete the service by entering the following command: 

    $ oc delete --filename service.yaml

  2. Delete the PingSource object by entering the following command: 

    $ oc delete --filename ping-source.yaml
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