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Custom event sources

If you need to ingress events from an event producer that is not included in Knative, or from a producer that emits events which are not in the CloudEvent format, you can do this by creating a custom event source. You can create a custom event source by using one of the following methods:

  • Use a PodSpecable object as an event source, by creating a sink binding.

  • Use a container as an event source, by creating a container source.

Sink binding

The SinkBinding object supports decoupling event production from delivery addressing. Sink binding is used to connect event producers to an event consumer, or sink. An event producer is a Kubernetes resource that embeds a PodSpec template and produces events. A sink is an addressable Kubernetes object that can receive events.

The SinkBinding object injects environment variables into the PodTemplateSpec of the sink, which means that the application code does not need to interact directly with the Kubernetes API to locate the event destination. These environment variables are as follows:

K_SINK

The URL of the resolved sink.

K_CE_OVERRIDES

A JSON object that specifies overrides to the outbound event.

The SinkBinding object currently does not support custom revision names for services.

Creating a sink binding by using YAML

Creating Knative resources by using YAML files uses a declarative API, which enables you to describe event sources declaratively and in a reproducible manner. To create a sink binding by using YAML, you must create a YAML file that defines an SinkBinding object, then apply it by using the oc apply command.

Prerequisites

  • The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on the cluster.

  • Install the OpenShift CLI (oc).

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. To check that sink binding is set up correctly, create a Knative event display service, or event sink, that dumps incoming messages to its log.

    1. Create a service YAML file:

      Example service YAML file
      apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/showcase

    2. Create the service:

      $ oc apply -f <filename>

  2. Create a sink binding instance that directs events to the service.

    1. Create a sink binding YAML file:

      Example service YAML file
      apiVersion: sources.knative.dev/v1alpha1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  subject:
    apiVersion: batch/v1
    kind: Job (1)
    selector:
      matchLabels:
        app: heartbeat-cron

  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display
      1 In this example, any Job with the label app: heartbeat-cron will be bound to the event sink.

    2. Create the sink binding:

      $ oc apply -f <filename>

  3. Create a CronJob object.

    1. Create a cron job YAML file:

      Example cron job YAML file
      apiVersion: batch/v1
kind: CronJob
metadata:
  name: heartbeat-cron
spec:
  # Run every minute
  schedule: "* * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: "true"
    spec:
      template:
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              image: quay.io/openshift-knative/heartbeats:latest
              args:
                - --period=1
              env:
                - name: ONE_SHOT
                  value: "true"
                - name: POD_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: POD_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace

      To use sink binding, you must manually add a bindings.knative.dev/include=true label to your Knative resources.

      For example, to add this label to a CronJob resource, add the following lines to the Job resource YAML definition:

        jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: "true"

    2. Create the cron job:

      $ oc apply -f <filename>

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

    $ oc get sinkbindings.sources.knative.dev bind-heartbeat -oyaml
    Example output
    spec:
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display
      namespace: default
  subject:
    apiVersion: batch/v1
    kind: Job
    namespace: default
    selector:
      matchLabels:
        app: heartbeat-cron
Verification

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

  1. Enter the command:

    $ oc get pods

  2. Enter the command:

    $ 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.eventing.samples.heartbeat
  source: https://knative.dev/eventing-contrib/cmd/heartbeats/#event-test/mypod
  id: 2b72d7bf-c38f-4a98-a433-608fbcdd2596
  time: 2019-10-18T15:23:20.809775386Z
  contenttype: application/json
Extensions,
  beats: true
  heart: yes
  the: 42
Data,
  {
    "id": 1,
    "label": ""
  }

Creating a sink binding by using the Knative CLI

You can use the kn source binding create command to create a sink binding by using the Knative (kn) CLI. Using the Knative CLI to create event sources provides a more streamlined and intuitive user interface than modifying YAML files directly.

Prerequisites

  • The OpenShift Serverless Operator, Knative Serving and Knative Eventing are installed on the cluster.

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

  • Install the Knative (kn) CLI.

  • Install the OpenShift CLI (oc).

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 check that sink binding is set up correctly, create a Knative event display service, or event sink, that dumps incoming messages to its log:

    $ kn service create event-display --image quay.io/openshift-knative/showcase

  2. Create a sink binding instance that directs events to the service:

    $ kn source binding create bind-heartbeat --subject Job:batch/v1:app=heartbeat-cron --sink ksvc:event-display

  3. Create a CronJob object.

    1. Create a cron job YAML file:

      Example cron job YAML file
      apiVersion: batch/v1
kind: CronJob
metadata:
  name: heartbeat-cron
spec:
  # Run every minute
  schedule: "* * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: "true"
    spec:
      template:
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              image: quay.io/openshift-knative/heartbeats:latest
              args:
                - --period=1
              env:
                - name: ONE_SHOT
                  value: "true"
                - name: POD_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: POD_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace

      To use sink binding, you must manually add a bindings.knative.dev/include=true label to your Knative CRs.

      For example, to add this label to a CronJob CR, add the following lines to the Job CR YAML definition:

        jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: "true"

    2. Create the cron job:

      $ oc apply -f <filename>

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

    $ kn source binding describe bind-heartbeat
    Example output
    Name:         bind-heartbeat
Namespace:    demo-2
Annotations:  sources.knative.dev/creator=minikube-user, sources.knative.dev/lastModifier=minikub ...
Age:          2m
Subject:
  Resource:   job (batch/v1)
  Selector:
    app:      heartbeat-cron
Sink:
  Name:       event-display
  Resource:   Service (serving.knative.dev/v1)

Conditions:
  OK TYPE     AGE REASON
  ++ Ready     2m
Verification

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

  • View the message dumper function logs by entering the following commands:

    $ oc get 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.eventing.samples.heartbeat
  source: https://knative.dev/eventing-contrib/cmd/heartbeats/#event-test/mypod
  id: 2b72d7bf-c38f-4a98-a433-608fbcdd2596
  time: 2019-10-18T15:23:20.809775386Z
  contenttype: application/json
Extensions,
  beats: true
  heart: yes
  the: 42
Data,
  {
    "id": 1,
    "label": ""
  }

Knative CLI sink flag

When you create an event source by using the Knative (kn) CLI, you can specify a sink where events are sent to from that resource by using the --sink flag. The sink can be any addressable or callable resource that can receive incoming events from other resources.

The following example creates a sink binding that uses a service, http://event-display.svc.cluster.local, as the sink:

Example command using the sink flag
$ kn source binding create bind-heartbeat \
  --namespace sinkbinding-example \
  --subject "Job:batch/v1:app=heartbeat-cron" \
  --sink http://event-display.svc.cluster.local \ (1)
  --ce-override "sink=bound"
1 svc in http://event-display.svc.cluster.local determines that the sink is a Knative service. Other default sink prefixes include channel, and broker.

Creating a sink binding by using the web console

After Knative Eventing is installed on your cluster, you can create a sink binding by using the web console. Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create an event source.

Prerequisites

  • You have logged in to the OpenShift Container Platform web console.

  • The OpenShift Serverless Operator, Knative Serving, and Knative Eventing are installed on your OpenShift Container Platform cluster.

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. Create a Knative service to use as a sink:

    1. In the Developer perspective, navigate to +Add → YAML.

    2. Copy the example YAML:

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

    3. Click Create.

  2. Create a CronJob resource that is used as an event source and sends an event every minute.

    1. In the Developer perspective, navigate to +Add → YAML.

    2. Copy the example YAML:

      apiVersion: batch/v1
kind: CronJob
metadata:
  name: heartbeat-cron
spec:
  # Run every minute
  schedule: "*/1 * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: true (1)
    spec:
      template:
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              image: quay.io/openshift-knative/heartbeats
              args:
              - --period=1
              env:
                - name: ONE_SHOT
                  value: "true"
                - name: POD_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: POD_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace
      1 Ensure that you include the bindings.knative.dev/include: true label. The default namespace selection behavior of OpenShift Serverless uses inclusion mode.

    3. Click Create.

  3. Create a sink binding in the same namespace as the service created in the previous step, or any other sink that you want to send events to.

    1. In the Developer perspective, navigate to +Add → Event Source. The Event Sources page is displayed.

    2. Optional: If you have multiple providers for your event sources, select the required provider from the Providers list to filter the available event sources from the provider.

    3. Select Sink Binding and then click Create Event Source. The Create Event Source page is displayed.

      You can configure the Sink Binding settings by using the Form view or YAML view and can switch between the views. The data is persisted when switching between the views.

    4. In the apiVersion field enter batch/v1.

    5. In the Kind field enter Job.

      The CronJob kind is not supported directly by OpenShift Serverless sink binding, so the Kind field must target the Job objects created by the cron job, rather than the cron job object itself.

    6. In the Target section, select your event sink. This can be either a Resource or a URI:

      1. Select Resource to use a channel, broker, or service as an event sink for the event source. In this example, the event-display service created in the previous step is used as the target Resource.

      2. Select URI to specify a Uniform Resource Identifier (URI) where the events are routed to.

    7. In the Match labels section:

      1. Enter app in the Name field.

      2. Enter heartbeat-cron in the Value field.

        The label selector is required when using cron jobs with sink binding, rather than the resource name. This is because jobs created by a cron job do not have a predictable name, and contain a randomly generated string in their name. For example, hearthbeat-cron-1cc23f.

    8. Click Create.

Verification

You can verify that the sink binding, sink, and cron job have been created and are working correctly by viewing the Topology page and pod logs.

  1. In the Developer perspective, navigate to Topology.

  2. View the sink binding, sink, and heartbeats cron job.

    View the sink binding and service in the Topology view

  3. Observe that successful jobs are being registered by the cron job once the sink binding is added. This means that the sink binding is successfully reconfiguring the jobs created by the cron job.

  4. Browse the event-display service to see events produced by the heartbeats cron job.

    View the events in the web UI

Sink binding reference

You can use a PodSpecable object as an event source by creating a sink binding. You can configure multiple parameters when creating a SinkBinding object.

SinkBinding objects support the following parameters:

Field Description Required or optional

apiVersion

Specifies the API version, for example sources.knative.dev/v1.

Required

kind

Identifies this resource object as a SinkBinding object.

Required

metadata

Specifies metadata that uniquely identifies the SinkBinding object. For example, a name.

Required

spec

Specifies the configuration information for this SinkBinding object.

Required

spec.sink

A reference to an object that resolves to a URI to use as the sink.

Required

spec.subject

References the resources for which the runtime contract is augmented by binding implementations.

Required

spec.ceOverrides

Defines overrides to control the output format and modifications to the event sent to the sink.

Optional

Subject parameter

The Subject parameter references the resources for which the runtime contract is augmented by binding implementations. You can configure multiple fields for a Subject definition.

The Subject definition supports the following fields:

Field Description Required or optional

apiVersion

API version of the referent.

Required

kind

Kind of the referent.

Required

namespace

Namespace of the referent. If omitted, this defaults to the namespace of the object.

Optional

name

Name of the referent.

Do not use if you configure selector.

selector

Selector of the referents.

Do not use if you configure name.

selector.matchExpressions

A list of label selector requirements.

Only use one of either matchExpressions or matchLabels.

selector.matchExpressions.key

The label key that the selector applies to.

Required if using matchExpressions.

selector.matchExpressions.operator

Represents a key’s relationship to a set of values. Valid operators are In, NotIn, Exists and DoesNotExist.

Required if using matchExpressions.

selector.matchExpressions.values

An array of string values. If the operator parameter value is In or NotIn, the values array must be non-empty. If the operator parameter value is Exists or DoesNotExist, the values array must be empty. This array is replaced during a strategic merge patch.

Required if using matchExpressions.

selector.matchLabels

A map of key-value pairs. Each key-value pair in the matchLabels map is equivalent to an element of matchExpressions, where the key field is matchLabels.<key>, the operator is In, and the values array contains only matchLabels.<value>.

Only use one of either matchExpressions or matchLabels.
Subject parameter examples

Given the following YAML, the Deployment object named mysubject in the default namespace is selected:

apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  subject:
    apiVersion: apps/v1
    kind: Deployment
    namespace: default
    name: mysubject
  ...

Given the following YAML, any Job object with the label working=example in the default namespace is selected:

apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  subject:
    apiVersion: batch/v1
    kind: Job
    namespace: default
    selector:
      matchLabels:
        working: example
  ...

Given the following YAML, any Pod object with the label working=example or working=sample in the default namespace is selected:

apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  subject:
    apiVersion: v1
    kind: Pod
    namespace: default
    selector:
      - matchExpression:
        key: working
        operator: In
        values:
          - example
          - sample
  ...

CloudEvent overrides

A ceOverrides definition provides overrides that control the CloudEvent’s output format and modifications sent to the sink. You can configure multiple fields for the ceOverrides definition.

A ceOverrides definition supports the following fields:

Field Description Required or optional

extensions

Specifies which attributes are added or overridden on the outbound event. Each extensions key-value pair is set independently on the event as an attribute extension.

Optional

Only valid CloudEvent attribute names are allowed as extensions. You cannot set the spec defined attributes from the extensions override configuration. For example, you can not modify the type attribute.
CloudEvent Overrides example
apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
  name: bind-heartbeat
spec:
  ...
  ceOverrides:
    extensions:
      extra: this is an extra attribute
      additional: 42

This sets the K_CE_OVERRIDES environment variable on the subject:

Example output
{ "extensions": { "extra": "this is an extra attribute", "additional": "42" } }

The include label

To use a sink binding, you need to do assign the bindings.knative.dev/include: "true" label to either the resource or the namespace that the resource is included in. If the resource definition does not include the label, a cluster administrator can attach it to the namespace by running:

$ oc label namespace <namespace> bindings.knative.dev/include=true

Integrating Service Mesh with a sink binding

Prerequisites

  • You have integrated Service Mesh with OpenShift Serverless.

Procedure

  1. Create a Service in a namespace that is a member of the ServiceMeshMemberRoll.

    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
  namespace: <namespace> (1)
spec:
  template:
    metadata:
      annotations:
        sidecar.istio.io/inject: "true" (2)
        sidecar.istio.io/rewriteAppHTTPProbers: "true"
    spec:
      containers:
      - image: quay.io/openshift-knative/showcase
    1 A namespace that is a member of the ServiceMeshMemberRoll.
    2 Injects Service Mesh sidecars into the Knative service pods.

  2. Apply the Service resource.

    $ oc apply -f <filename>

  3. Create a SinkBinding resource.

    apiVersion: sources.knative.dev/v1
kind: SinkBinding
metadata:
  name: bind-heartbeat
  namespace: <namespace> (1)
spec:
  subject:
    apiVersion: batch/v1
    kind: Job (2)
    selector:
      matchLabels:
        app: heartbeat-cron

  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display
    1 A namespace that is a member of the ServiceMeshMemberRoll.
    2 In this example, any Job with the label app: heartbeat-cron is bound to the event sink.

  4. Apply the SinkBinding resource.

    $ oc apply -f <filename>

  5. Create a CronJob:

    apiVersion: batch/v1
kind: CronJob
metadata:
  name: heartbeat-cron
  namespace: <namespace> (1)
spec:
  # Run every minute
  schedule: "* * * * *"
  jobTemplate:
    metadata:
      labels:
        app: heartbeat-cron
        bindings.knative.dev/include: "true"
    spec:
      template:
        metadata:
          annotations:
            sidecar.istio.io/inject: "true" (2)
            sidecar.istio.io/rewriteAppHTTPProbers: "true"
        spec:
          restartPolicy: Never
          containers:
            - name: single-heartbeat
              image: quay.io/openshift-knative/heartbeats:latest
              args:
                - --period=1
              env:
                - name: ONE_SHOT
                  value: "true"
                - name: POD_NAME
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.name
                - name: POD_NAMESPACE
                  valueFrom:
                    fieldRef:
                      fieldPath: metadata.namespace
    1 A namespace that is a member of the ServiceMeshMemberRoll.
    2 Injects Service Mesh sidecars into the CronJob pods.

  6. Apply the CronJob resource.

    $ oc apply -f <filename>
Verification

To verify that the events were sent to the Knative event sink, look at the message dumper function logs.

  1. Enter the following command:

    $ oc get pods

  2. Enter the following command:

    $ 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.eventing.samples.heartbeat
  source: https://knative.dev/eventing/test/heartbeats/#event-test/mypod
  id: 2b72d7bf-c38f-4a98-a433-608fbcdd2596
  time: 2019-10-18T15:23:20.809775386Z
  contenttype: application/json
Extensions,
  beats: true
  heart: yes
  the: 42
Data,
  {
    "id": 1,
    "label": ""
  }
Additional resources

Container source

Container sources create a container image that generates events and sends events to a sink. You can use a container source to create a custom event source, by creating a container image and a ContainerSource object that uses your image URI.

Guidelines for creating a container image

Two environment variables are injected by the container source controller: K_SINK and K_CE_OVERRIDES. These variables are resolved from the sink and ceOverrides spec, respectively. Events are sent to the sink URI specified in the K_SINK environment variable. The message must be sent as a POST using the CloudEvent HTTP format.

Example container images

The following is an example of a heartbeats container image:

package main

import (
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"log"
	"os"
	"strconv"
	"time"

	duckv1 "knative.dev/pkg/apis/duck/v1"

	cloudevents "github.com/cloudevents/sdk-go/v2"
	"github.com/kelseyhightower/envconfig"
)

type Heartbeat struct {
	Sequence int    `json:"id"`
	Label    string `json:"label"`
}

var (
	eventSource string
	eventType   string
	sink        string
	label       string
	periodStr   string
)

func init() {
	flag.StringVar(&eventSource, "eventSource", "", "the event-source (CloudEvents)")
	flag.StringVar(&eventType, "eventType", "dev.knative.eventing.samples.heartbeat", "the event-type (CloudEvents)")
	flag.StringVar(&sink, "sink", "", "the host url to heartbeat to")
	flag.StringVar(&label, "label", "", "a special label")
	flag.StringVar(&periodStr, "period", "5", "the number of seconds between heartbeats")
}

type envConfig struct {
	// Sink URL where to send heartbeat cloud events
	Sink string `envconfig:"K_SINK"`

	// CEOverrides are the CloudEvents overrides to be applied to the outbound event.
	CEOverrides string `envconfig:"K_CE_OVERRIDES"`

	// Name of this pod.
	Name string `envconfig:"POD_NAME" required:"true"`

	// Namespace this pod exists in.
	Namespace string `envconfig:"POD_NAMESPACE" required:"true"`

	// Whether to run continuously or exit.
	OneShot bool `envconfig:"ONE_SHOT" default:"false"`
}

func main() {
	flag.Parse()

	var env envConfig
	if err := envconfig.Process("", &env); err != nil {
		log.Printf("[ERROR] Failed to process env var: %s", err)
		os.Exit(1)
	}

	if env.Sink != "" {
		sink = env.Sink
	}

	var ceOverrides *duckv1.CloudEventOverrides
	if len(env.CEOverrides) > 0 {
		overrides := duckv1.CloudEventOverrides{}
		err := json.Unmarshal([]byte(env.CEOverrides), &overrides)
		if err != nil {
			log.Printf("[ERROR] Unparseable CloudEvents overrides %s: %v", env.CEOverrides, err)
			os.Exit(1)
		}
		ceOverrides = &overrides
	}

	p, err := cloudevents.NewHTTP(cloudevents.WithTarget(sink))
	if err != nil {
		log.Fatalf("failed to create http protocol: %s", err.Error())
	}

	c, err := cloudevents.NewClient(p, cloudevents.WithUUIDs(), cloudevents.WithTimeNow())
	if err != nil {
		log.Fatalf("failed to create client: %s", err.Error())
	}

	var period time.Duration
	if p, err := strconv.Atoi(periodStr); err != nil {
		period = time.Duration(5) * time.Second
	} else {
		period = time.Duration(p) * time.Second
	}

	if eventSource == "" {
		eventSource = fmt.Sprintf("https://knative.dev/eventing-contrib/cmd/heartbeats/#%s/%s", env.Namespace, env.Name)
		log.Printf("Heartbeats Source: %s", eventSource)
	}

	if len(label) > 0 && label[0] == '"' {
		label, _ = strconv.Unquote(label)
	}
	hb := &Heartbeat{
		Sequence: 0,
		Label:    label,
	}
	ticker := time.NewTicker(period)
	for {
		hb.Sequence++

		event := cloudevents.NewEvent("1.0")
		event.SetType(eventType)
		event.SetSource(eventSource)
		event.SetExtension("the", 42)
		event.SetExtension("heart", "yes")
		event.SetExtension("beats", true)

		if ceOverrides != nil && ceOverrides.Extensions != nil {
			for n, v := range ceOverrides.Extensions {
				event.SetExtension(n, v)
			}
		}

		if err := event.SetData(cloudevents.ApplicationJSON, hb); err != nil {
			log.Printf("failed to set cloudevents data: %s", err.Error())
		}

		log.Printf("sending cloudevent to %s", sink)
		if res := c.Send(context.Background(), event); !cloudevents.IsACK(res) {
			log.Printf("failed to send cloudevent: %v", res)
		}

		if env.OneShot {
			return
		}

		// Wait for next tick
		<-ticker.C
	}
}

The following is an example of a container source that references the previous heartbeats container image:

apiVersion: sources.knative.dev/v1
kind: ContainerSource
metadata:
  name: test-heartbeats
spec:
  template:
    spec:
      containers:
        # This corresponds to a heartbeats image URI that you have built and published
        - image: gcr.io/knative-releases/knative.dev/eventing/cmd/heartbeats
          name: heartbeats
          args:
            - --period=1
          env:
            - name: POD_NAME
              value: "example-pod"
            - name: POD_NAMESPACE
              value: "event-test"
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: showcase
...

Creating and managing container sources by using the Knative CLI

You can use the kn source container commands to create and manage container sources by using the Knative (kn) CLI. Using the Knative CLI to create event sources provides a more streamlined and intuitive user interface than modifying YAML files directly.

Create a container source
$ kn source container create <container_source_name> --image <image_uri> --sink <sink>
Delete a container source
$ kn source container delete <container_source_name>
Describe a container source
$ kn source container describe <container_source_name>
List existing container sources
$ kn source container list
List existing container sources in YAML format
$ kn source container list -o yaml
Update a container source

This command updates the image URI for an existing container source:

$ kn source container update <container_source_name> --image <image_uri>

Creating a container source by using the web console

After Knative Eventing is installed on your cluster, you can create a container source by using the web console. Using the OpenShift Container Platform web console provides a streamlined and intuitive user interface to create an event source.

Prerequisites

  • You have logged in to the OpenShift Container Platform web console.

  • The OpenShift Serverless Operator, Knative Serving, and Knative Eventing are installed on your OpenShift Container Platform cluster.

  • You have created a project or have access to a project with the appropriate roles and permissions to create applications and other workloads in OpenShift Container Platform.

Procedure

  1. In the Developer perspective, navigate to +Add → Event Source. The Event Sources page is displayed.

  2. Select Container Source and then click Create Event Source. The Create Event Source page is displayed.

  3. Configure the Container Source settings by using the Form view or YAML view:

    You can switch between the Form view and YAML view. The data is persisted when switching between the views.

    1. In the Image field, enter the URI of the image that you want to run in the container created by the container source.

    2. In the Name field, enter the name of the image.

    3. Optional: In the Arguments field, enter any arguments to be passed to the container.

    4. Optional: In the Environment variables field, add any environment variables to set in the container.

    5. In the Target section, select your event sink. This can be either a Resource or a URI:

      1. Select Resource to use a channel, broker, or service as an event sink for the event source.

      2. Select URI to specify a Uniform Resource Identifier (URI) where the events are routed to.

  4. After you have finished configuring the container source, click Create.

Container source reference

You can use a container as an event source, by creating a ContainerSource object. You can configure multiple parameters when creating a ContainerSource object.

ContainerSource objects support the following fields:

Field Description Required or optional

apiVersion

Specifies the API version, for example sources.knative.dev/v1.

Required

kind

Identifies this resource object as a ContainerSource object.

Required

metadata

Specifies metadata that uniquely identifies the ContainerSource object. For example, a name.

Required

spec

Specifies the configuration information for this ContainerSource object.

Required

spec.sink

A reference to an object that resolves to a URI to use as the sink.

Required

spec.template

A template spec for the ContainerSource object.

Required

spec.ceOverrides

Defines overrides to control the output format and modifications to the event sent to the sink.

Optional
Template parameter example
apiVersion: sources.knative.dev/v1
kind: ContainerSource
metadata:
  name: test-heartbeats
spec:
  template:
    spec:
      containers:
        - image: quay.io/openshift-knative/heartbeats:latest
          name: heartbeats
          args:
            - --period=1
          env:
            - name: POD_NAME
              value: "mypod"
            - name: POD_NAMESPACE
              value: "event-test"
  ...

CloudEvent overrides

A ceOverrides definition provides overrides that control the CloudEvent’s output format and modifications sent to the sink. You can configure multiple fields for the ceOverrides definition.

A ceOverrides definition supports the following fields:

Field Description Required or optional

extensions

Specifies which attributes are added or overridden on the outbound event. Each extensions key-value pair is set independently on the event as an attribute extension.

Optional

Only valid CloudEvent attribute names are allowed as extensions. You cannot set the spec defined attributes from the extensions override configuration. For example, you can not modify the type attribute.
CloudEvent Overrides example
apiVersion: sources.knative.dev/v1
kind: ContainerSource
metadata:
  name: test-heartbeats
spec:
  ...
  ceOverrides:
    extensions:
      extra: this is an extra attribute
      additional: 42

This sets the K_CE_OVERRIDES environment variable on the subject:

Example output
{ "extensions": { "extra": "this is an extra attribute", "additional": "42" } }

Integrating Service Mesh with ContainerSource

Prerequisites

  • You have integrated Service Mesh with OpenShift Serverless.

Procedure

  1. Create a Service in a namespace that is a member of the ServiceMeshMemberRoll.

    apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
  namespace: <namespace> (1)
spec:
  template:
    metadata:
      annotations:
        sidecar.istio.io/inject: "true" (2)
        sidecar.istio.io/rewriteAppHTTPProbers: "true"
    spec:
      containers:
      - image: quay.io/openshift-knative/showcase
    1 A namespace that is a member of the ServiceMeshMemberRoll.
    2 Injects Service Mesh sidecars into the Knative service pods.

  2. Apply the Service resource.

    $ oc apply -f <filename>

  3. Create a ContainerSource object in a namespace that is a member of the ServiceMeshMemberRoll and sink set to the event-display.

    apiVersion: sources.knative.dev/v1
kind: ContainerSource
metadata:
  name: test-heartbeats
  namespace: <namespace> (1)
spec:
  template:
    metadata: (2)
      annotations:
        sidecar.istio.io/inject: "true"
        sidecar.istio.io/rewriteAppHTTPProbers: "true"
    spec:
      containers:
        - image: quay.io/openshift-knative/heartbeats:latest
          name: heartbeats
          args:
            - --period=1s
          env:
            - name: POD_NAME
              value: "example-pod"
            - name: POD_NAMESPACE
              value: "event-test"
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display
    1 A namespace is part of the ServiceMeshMemberRoll.
    2 Enables Service Mesh integration with a ContainerSource object.

  4. Apply the ContainerSource resource.

    $ oc apply -f <filename>
Verification

To verify that the events were sent to the Knative event sink, look at the message dumper function logs.

  1. Enter the following command:

    $ oc get pods

  2. Enter the following command:

    $ 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.eventing.samples.heartbeat
  source: https://knative.dev/eventing/test/heartbeats/#event-test/mypod
  id: 2b72d7bf-c38f-4a98-a433-608fbcdd2596
  time: 2019-10-18T15:23:20.809775386Z
  contenttype: application/json
Extensions,
  beats: true
  heart: yes
  the: 42
Data,
  {
    "id": 1,
    "label": ""
  }
Additional resources