---
audience: developer
components:
  - eventing
function: how-to
---

# Create a ContainerSource

![API version v1](https://img.shields.io/badge/API_Version-v1-green?style=flat-square)

The ContainerSource object starts a container image that generates events and
sends messages to a sink URI. You can also use ContainerSource to support your
own event sources in Knative.

To create a custom event source using ContainerSource, you must create a
container image, and a ContainerSource that uses your image URI.

## Before you begin

Before you can create a ContainerSource object, you must have [Knative Eventing](../../../install/yaml-install/eventing/install-eventing-with-yaml.md) installed on your cluster.

## Develop, build and publish a container image

You can develop a container image by using any language, and can build and publish your image by using any tools you like. The following are some basic guidelines:

- Two environments variables are injected by the ContainerSource controller; `K_SINK` and `K_CE_OVERRIDES`, resolved from `spec.sink` and `spec.ceOverrides` respectively.
- The event messages are sent to the sink URI specified in `K_SINK`. The message must be sent as a POST in [CloudEvents HTTP format](https://github.com/cloudevents/spec/blob/v1.0.2/cloudevents/bindings/http-protocol-binding.md).

## Create a ContainerSource object

1. Build an image of your event source and publish it to your image repository. Your image must read the environment variable `K_SINK` and post messages to the URL specified in `K_SINK`.

    You can use the following YAML to deploy a demo `heartbeats` event source:

    ```yaml
    apiVersion: sources.knative.dev/v1
    kind: ContainerSource
    metadata:
      name: heartbeat-source
    spec:
      template:
        spec:
          containers:
            - image: gcr.io/knative-nightly/knative.dev/eventing/cmd/heartbeats:latest
              name: heartbeats
      sink:
        ref:
          apiVersion: serving.knative.dev/v1
          kind: Service
          name: event-display
    ```

1. Create a namespace for your ContainerSource by running the command:

    ```bash
    kubectl create namespace <namespace>
    ```

    Where `<namespace>` is the namespace that you want your ContainerSource to use. For example, `heartbeat-source`.

1. Create a sink. If you do not already have a sink, you can use the following Knative Service, which dumps incoming messages into its log:

    !!! note
        To create a Knative service you must have Knative Serving installed on your cluster.

    === "kn"
        - To create a sink, run the command:

            ```bash
            kn service create event-display --port 8080 --image gcr.io/knative-releases/knative.dev/eventing/cmd/event_display
            ```

    === "YAML"
        1. Create a YAML file using the following example:

            ```yaml
            apiVersion: apps/v1
            kind: Deployment
            metadata:
              name: event-display
            spec:
              replicas: 1
              selector:
                matchLabels: &labels
                  app: event-display
              template:
                metadata:
                  labels: *labels
                spec:
                  containers:
                    - name: event-display
                      image: gcr.io/knative-releases/knative.dev/eventing/cmd/event_display

            ---

            kind: Service
            apiVersion: v1
            metadata:
              name: event-display
            spec:
              selector:
                app: event-display
              ports:
              - protocol: TCP
                port: 80
                targetPort: 8080
            ```

        1. Apply the YAML file by running the command:

            ```bash
            kubectl apply -f <filename>.yaml
            ```
            Where `<filename>` is the name of the file you created in the previous step.


1. Create a concrete ContainerSource with specific arguments and environment settings:

    === "kn"
        - To create the ContainerSource, run the command:

            ```bash
            kn source container create <name> --image <image-uri> --sink <sink> -e POD_NAME=<pod-name> -e POD_NAMESPACE=<pod-namespace>
            ```
            Where:

            - `<name>` is the name you want for your ContainerSource object,
            for example, `test-heartbeats`.
            - `<image-uri>` corresponds to the image URI you built and published
            in step 1, for example, `gcr.io/knative-nightly/knative.dev/eventing/cmd/heartbeats`.
            - `<pod-name>` is the name of the Pod that the container runs in, for example, `mypod`.
            - `<pod-namespace>` is the namespace that the Pod runs in, for example, `event-test`.
            - `<sink>` is the name of your sink, for example, `event-display`.
            For a list of available options, see the [Knative client documentation](https://github.com/knative/client/blob/main/docs/cmd/kn_source_container_create.md#kn-source-container-create).

    === "YAML"
        1. Create a YAML file using the following template:

            ```yaml
            apiVersion: sources.knative.dev/v1
            kind: ContainerSource
            metadata:
              name: <containersource-name>
            spec:
              template:
                spec:
                  containers:
                    - image: <event-source-image-uri>
                      name: <container-name>
                      env:
                        - name: POD_NAME
                          value: "<pod-name>"
                        - name: POD_NAMESPACE
                          value: "<pod-namespace>"
              sink:
                ref:
                  apiVersion: v1
                  kind: Service
                  name: <sink>
            ```
            Where:

            - `<namespace>` is the namespace you created for your ContainerSource,
            for example, `containersource-example`.
            - `<containersource-name>` is the name you want for your ContainerSource,
            for example, `test-heartbeats`.
            - `<event-source-image-uri>` corresponds to the image URI you built and published
            in step 1, for example, `gcr.io/knative-nightly/knative.dev/eventing/cmd/heartbeats`.
            - `<container-name>` is the name of your event source, for example, `heartbeats`.
            - `<pod-name>` is the name of the Pod that the container runs in, for example, `mypod`.
            - `<pod-namespace>` is the namespace that the Pod runs in, for example, `event-test`.
            - `<sink>` is the name of your sink, for example, `event-display`.

            For more information about the fields you can configure for the ContainerSource
            object, see [ContainerSource Reference](reference.md).

        1. Apply the YAML file by running the command:

            ```bash
            kubectl apply -f <filename>.yaml
            ```
            Where `<filename>` is the name of the file you created in the previous step.

    !!! note
        Arguments and environment variables are set and are passed to the container.

## Verify the ContainerSource object

1. View the logs for your event consumer by running the command:

    ```shell
    kubectl -n <namespace> logs -l <pod-name> --tail=200
    ```
    Where:

    - `<namespace>` is the namespace that contains the ContainerSource object.
    - `<pod-name>` is the name of the Pod that the container runs in.

    For example:

    ```shell
    $ kubectl -n containersource-example logs -l app=event-display --tail=200
    ```

1. Verify that the output returns the properties of the events that your
ContainerSource sent to your sink.
In the following example, the command has returned the `Attributes` and `Data` properties
of the events that the ContainerSource sent to the `event-display` Service:

    ```
    ☁️  cloudevents.Event
    Validation: valid
    Context Attributes,
      specversion: 1.0
      type: dev.knative.eventing.samples.heartbeat
      source: https://knative.dev/eventing/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": ""
      }
    ```

## Delete the ContainerSource object

To delete the ContainerSource object and all of the related resources in the
namespace:

- Delete the namespace by running the command:

    ```shell
    kubectl delete namespace <namespace>
    ```

    Where `<namespace>` is the namespace that contains the ContainerSource object.

## Reference Documentation

See the [ContainerSource reference](reference.md).
