Container Source Example

ContainerSource will start a container image which will generate events under certain situations and send messages to a sink URI. It also can be an easy way to support your own event sources in Knative. This guide shows how to configure ContainerSource as an event source for functions and summarizes guidelines for creating your own event source as a ContainerSource.

Create a heartbeats ContainerSource

Prerequisites

  1. Setup Knative Serving.
  2. Setup Knative Eventing and Sources.

Prepare the heartbeats image

Knative event-sources has a sample of heartbeats event source. You could clone the source codes by

git clone -b "{{< branch >}}" https://github.com/knative/eventing-contrib.git

And then build a heartbeats image and publish to your image repo with

ko publish knative.dev/eventing-contrib/cmd/heartbeats

Note: ko publish requires:

  • KO_DOCKER_REPO to be set. (e.g. gcr.io/[gcloud-project] or docker.io/<username>)
  • you to be authenticated with your KO_DOCKER_REPO
  • docker to be installed

Create a Knative Service

In order to verify ContainerSource is working, we will create a Event Display Service that dumps incoming messages to its log.

apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: event-display
spec:
  template:
    spec:
      containers:
        - image: gcr.io/knative-releases/knative.dev/eventing-contrib/cmd/event_display

Use following command to create the service from service.yaml:

kubectl apply --filename service.yaml

The status of the created service can be seen using:

kubectl get ksvc

NAME            URL                                           LATESTCREATED         LATESTREADY           READY   REASON
event-display   http://event-display.default.1.2.3.4.xip.io   event-display-gqjbw   event-display-gqjbw   True

Create a ContainerSource using the heartbeats image

In order to run the heartbeats container as an event source, you have to create a concrete ContainerSource with specific arguments and environment settings. Be sure to replace heartbeats_image_uri with a valid uri for your heartbeats image in your image repo in heartbeats-source.yaml file. Note that arguments and environment variables are set and will be passed to the container.

apiVersion: sources.knative.dev/v1beta1
kind: ContainerSource
metadata:
  name: test-heartbeats
spec:
  template:
    spec:
      containers:
        - image: <heartbeats_image_uri>
          name: heartbeats
          args:
            - --period=1
          env:
            - name: POD_NAME
              value: "mypod"
            - name: POD_NAMESPACE
              value: "event-test"
  sink:
    ref:
      apiVersion: serving.knative.dev/v1
      kind: Service
      name: event-display

Use the following command to create the event source from heartbeats-source.yaml:

kubectl apply --filename heartbeats-source.yaml

Verify

We will verify that the message was sent to the Knative eventing system by looking at event-display service logs.

kubectl logs -l serving.knative.dev/service=event-display -c user-container --since=10m

You should see log lines showing the request headers and body of the event message sent by the heartbeats source to the display function:

☁️  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": 2,
    "label": ""
  }

Create a new event source using ContainerSource

In order to create a new event source using ContainerSource, you will create a container image at first, and then create a ContainerSource with the image uri and specify the values of parameters.

Develop, build and publish a container image

The container image can be developed with any language, build and publish with any tools you like. Here are some basic guidelines:

  • The container image must have a main method to start with.
  • The main method will accept parameters from arguments and environment variables.
  • Two environments variables will be injected by the ContainerSource controller, K_SINK and K_CE_OVERRIDES, resolved from spec.sink and spec.ceOverrides respectively.
  • The event messages shall be sent to the sink URI specified in K_SINK. The message can be any format. CloudEvents format is recommended.

heartbeats event source is a sample for your reference.

Create the ContainerSource using this container image

When the container image is ready, a YAML file will be used to create a concrete ContainerSource. Use heartbeats-source.yaml as a sample for reference. Learn more about the ContainerSource specification.