Creating a Channel using cluster or namespace defaults

Developers can create Channels of any supported implementation type by creating an instance of a Channel object.

To create a Channel:

  • Create a Channel object by running:

    1. kubectl apply -f <<EOF
    2. apiVersion: messaging.knative.dev/v1
    3. kind: Channel
    4. metadata:
    5.   name: <example-channel>
    6.   namespace: <namespace>
    7. EOF

    Where:

    • <example-channel> is the name of the Channel you want to create.
    • <namespace> is the name of your target namespace.

If you create this object in the default namespace, according to the default ConfigMap example in Channel types and defaults, it is an InMemoryChannel Channel implementation.

After the Channel object is created, a mutating admission webhook sets the spec.channelTemplate based on the default Channel implementation:

  1. apiVersion: messaging.knative.dev/v1
  2. kind: Channel
  3. metadata:
  4.   name: <example-channel>
  5.   namespace: <namespace>
  6. spec:
  7.   channelTemplate:
  8.     apiVersion: messaging.knative.dev/v1
  9.     kind: <channel-template-kind>

Where:

  • <example-channel> is the name of the Channel you want to create.
  • <namespace> is the name of your target namespace.
  • <channel-template-kind> is the kind of Channel, such as InMemoryChannel or KafkaChannel, based on the default ConfigMap. See an example in Channel types and defaults.

Note

The spec.channelTemplate property cannot be changed after creation, because it is set by the default Channel mechanism, not the user.

The Channel controller creates a backing Channel instance based on the spec.channelTemplate.

When this mechanism is used two objects are created; a generic Channel object and an InMemoryChannel object. The generic object acts as a proxy for the InMemoryChannel object by copying its Subscriptions to, and setting its status to, that of the InMemoryChannel object.

Note

Defaults are only applied by the webhook when a Channel or Sequence is initially created. If the default settings are changed, the new defaults will only be applied to newly created Channels, Brokers, or Sequences. Existing resources are not updated automatically to use the new configuration.