Default config (config-br-defaults)

Knative provides a ConfigMap which makes it easier to create Brokers by providing default values when Brokers are created. You can control which Broker implementations are used and how they are configured by modifying this file. You have the flexibility to control the defaults both at the cluster level (each Broker created in the cluster) as well as at the namespace level (override the behaviour for certain namespaces).

Format of the file

Let's look at the ConfigMap that comes out of the box when you install a release (v0.16.0 in this example):

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-br-defaults
  namespace: knative-eventing
  labels:
    eventing.knative.dev/release: devel
data:
  # Configuration for defaulting channels that do not specify CRD implementations.
  default-br-config: |
    clusterDefault:
      brokerClass: MTChannelBasedBroker
      apiVersion: v1
      kind: ConfigMap
      name: config-br-default-channel
      namespace: knative-eventing

This means that any Broker created without a specific BrokerClass annotation will use MTChannelBasedBroker, and any Broker without a spec.config will have spec.config like so:

spec:
  config:
    apiVersion: v1
    kind: ConfigMap
    name: config-br-default-channel
    namespace: knative-eventing

Changing the default BrokerClass

Changing the default BrokerClass for the cluster

If you have installed a different Broker, or multiple, you can change the default Broker used at the cluster level and by namespace. If you for example have installed MT Channel Based Broker as well as YourBroker and would prefer that by default any Broker created uses YourBroker you could modify the ConfigMap to look like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-br-defaults
  namespace: knative-eventing
  labels:
    eventing.knative.dev/release: devel
data:
  # Configuration for defaulting channels that do not specify CRD implementations.
  default-br-config: |
    clusterDefault:
      brokerClass: YourBroker

Now every Broker created in the cluster without the BrokerClass annotation will be using YourBroker as the Broker implementation. Note that you can always use a different implementation by explicitly specifying the BrokerClass annotation when you create a Broker.

Changing the default BrokerClass for namespaces

As mentioned, you can also control the defaulting behaviour for some set of namespaces. So, if for example, you wanted to use YourBroker for all the other Brokers created, but wanted to use MTChannelBasedBroker for the following namespaces: namespace1 and namespace2. You would modify the config map like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-br-defaults
  namespace: knative-eventing
  labels:
    eventing.knative.dev/release: devel
data:
  # Configuration for defaulting channels that do not specify CRD implementations.
  default-br-config: |
    clusterDefault:
      brokerClass: YourBroker
    namespaceDefaults:
      namespace1:
        brokerClass: MTChannelBasedBroker
      namespace2:
        brokerClass: MTChannelBasedBroker

Changing the default configuration of the Broker

Changing the default configuration for the cluster

You can also control Broker configuration defaulting behaviour by specifying what gets defaulted into a broker.spec.config if left empty when being created.

If you have installed a different Channel implementation (for example Kafka), and by default would like to use that for any Broker created you could change the ConfigMap to look like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-br-defaults
  namespace: knative-eventing
  labels:
    eventing.knative.dev/release: devel
data:
  # Configuration for defaulting channels that do not specify CRD implementations.
  default-br-config: |
    clusterDefault:
      brokerClass: MTChannelBasedBroker
      apiVersion: v1
      kind: ConfigMap
      name: config-kafka-channel
      namespace: knative-eventing

Now every Broker created in the cluster without spec.config will be configured to use config-kafka-channel ConfigMap. Note that you can always still explicitly specify a different configuration for any given Broker by specifying it in the spec.config.

Changing the default configuration for namespaces

As mentioned, you can also control the defaulting behaviour for some set of namespaces. So, if for example, you wanted to use config-kafka-channel for all the other Brokers created, but wanted to use config-br-default-channel config the following namespaces: namespace3 and namespace4. You would modify the ConfigMap like this:

apiVersion: v1
kind: ConfigMap
metadata:
  name: config-br-defaults
  namespace: knative-eventing
  labels:
    eventing.knative.dev/release: devel
data:
  # Configuration for defaulting channels that do not specify CRD implementations.
  default-br-config: |
    clusterDefault:
      brokerClass: MTChannelBasedBroker
      apiVersion: v1
      kind: ConfigMap
      name: config-kafka-channel
      namespace: knative-eventing
    namespaceDefaults:
      namespace3:
        apiVersion: v1
        kind: ConfigMap
        name: config-br-default-channel
        namespace: knative-eventing
      namespace4:
        apiVersion: v1
        kind: ConfigMap
        name: config-br-default-channel
        namespace: knative-eventing

Note that we do not override the brokerClass for these namespaces. The brokerClass and config are independently configurable.