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:

1. Create a YAML file for the Channel object using the following template:

   apiVersion: messaging.knative.dev/v1
   kind: Channel
   metadata:
     name: <example-channel>
     namespace: <namespace>
   

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

2. Apply the YAML file by running the command:

   kubectl apply -f <filename>.yaml
   

   Where <filename> is the name of the file you created in the previous step.

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:

apiVersion: messaging.knative.dev/v1
kind: Channel
metadata:
  name: <example-channel>
  namespace: <namespace>
spec:
  channelTemplate:
    apiVersion: messaging.knative.dev/v1
    kind: <channel-template-kind>

• <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.

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.