Chapter 11. Event sources

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.

SinkBinding 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 kn 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:

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.

11.2.1. Listing available event source types using kn

Procedure

  • List the available event source types in the terminal: 

    $ kn source list-types

    Example output

    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

  • You can also list available event source types in YAML format: 

    $ kn source list-types -o yaml

11.2.2. Listing available event sources using kn

  • List available event sources by entering 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

11.2.2.1. Listing event sources of a specific type only

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

  • List available event sources of type PingSource by entering the following command: 

    $ 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 ApiServerSource

ApiServerSource is an event source that can be used to connect an event sink, such as a Knative service, to the Kubernetes API server. ApiServerSource 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 ApiServerSource with the Knative CLI (kn)

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

Prerequisites

  • You must have OpenShift Serverless, the Knative Serving and Eventing components, and the kn CLI installed.

Procedure

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

    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 ApiServerSource.
    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.

    Create the service account, role binding and cluster binding: 

    $ oc apply -f authentication.yaml

  2. Create an ApiServerSource 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. To check that the ApiServerSource is set up correctly, 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:latest

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

    $ kn source apiserver describe <source_name>

    Example output

    Name:                mysource
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 the ApiServerSource using the Knative CLI (kn)

This section describes the steps used to delete the ApiServerSource, trigger, service, service account, cluster role, and cluster binding using 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 event 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. Using the ApiServerSource with the YAML method

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

Prerequisites

  • You will need to have a Knative Serving and Eventing installation.
  • You will need to have created the default broker in the same namespace as the one defined in the ApiServerSource YAML file.

Procedure

  1. To create a service account, role, and role binding for the ApiServerSource, 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 ApiServerSource.
    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 event source, 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 ApiServerSource 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 ApiServerSource

This section describes how to delete the ApiServerSource, 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 event 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 PingSource

A PingSource is used to periodically send ping events with a constant payload to an event consumer, and can be used to schedule sending events, similar to a timer.

Example PingSource YAML

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. Using a PingSource with the kn CLI

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

Prerequisites

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

Procedure

  1. To verify that the PingSource 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 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

Verfication steps

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

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 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 PingSource

  1. Delete the PingSource: 

    $ 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. Using a PingSource with YAML

The following sections describe how to create, verify and remove a basic PingSource 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 PingSource 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. Create the service: 

      $ oc apply --filename service.yaml

  2. For each set of ping events that you want to request, create a PingSource 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. Create the PingSource: 

      $ oc apply --filename ping-source.yaml

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

    $ 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

Verfication steps

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

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 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 by entering the following command: 

    $ oc delete --filename ping-source.yaml