Issues with kafka channel example doc

[Shashankft9]

Issues with https://knative.dev/docs/eventing/samples/kafka/channel/:

• the second step in the prerequisites should land to the actual kafka channel installation page: https://knative.dev/docs/admin/install/eventing/install-eventing-with-yaml/#optional-install-a-default-channel-messaging-layer
  there should be a third prerequisite of installing a broker layer (mt channel based, since the doc demonstrates that)
• A pointer before the "configuring knative broker" step starts, talking about the use of Subscription CRD, so that it illustrates the channel-subscription concept also. I got a bit confused without it, I was unable to understand why there was no subscription there since there are majorly 2 models here - channel-subscription and broker-trigger.
• In the broker configuration, the first step should be to edit the configmap, so that the broker creates a kafka channel (topic) otherwise it would create imc - by default in knative installation: mt channel based broker uses config-br-defaults cm, and that has clusterDefault with config-br-default-channel cm, which further has InMemoryChannel as kind.
• After creating broker, in the doc currently it says that two pods will be created - default-broker-filter and default-broker-ingress which has changed to mt-broker-filter and mt-broker-ingress respectively.
• And the topic created with one broker is just one: knative-messaging-kafka.default.default-kne-trigger (I think the -ingress topic was removed some time ago(?), followed up some slack threads)
• Now in the yaml apply steps, can there be the complete yaml files instead, like in the other places in that same page?

Additional Info

Additional context
talked about this here too: https://knative.slack.com/archives/C017X0PFC0P/p1627580394220300
I will be sending a PR with probable fixes, in the mean time please feel free to correct me if the above listed issues are infact correct, thanks!

Install information:

• Knative Version: v0.24

[abrennan89]

Added this to the epic; folks seem to be reporting a lot of similar issues for the Kafka pages.

[Shashankft9]

hey @abrennan89, I think most of these issues can be covered in #4028 - so I shared my opinions on there.
Except the second point about subscription, maybe that can go in a separate PR if required.

[RichardJJG]

@abrennan89, did this issue get resolved as part #4028?

[github-actions]

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[Shashankft9]

/reopen

[knative-prow-robot]

@Shashankft9: Reopened this issue.

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/reopen

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