Question: Scaling kafka-channel-dispatcher without KEDA

[joke]

Problem

Is it possible to set the number of replicas for the kafka-channel-dispatcher without using KEDA?

Just setting the number of replicas doesn't work.

Persona:
System Operator

Additional context (optional)
Version 1.17

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[creydr]

/cc @Cali0707 can you give some insights here?

[Cali0707]

Hey - it is possible, but it needs to be done indirectly. Probably the easiest way should be to adjust this config value:

eventing-kafka-broker/control-plane/config/eventing-kafka-broker/200-controller/500-controller.yaml

Lines 155 to 162 in 0dd0a03

	# The minimum number of dispatchers instances to run. This configuration helps with configuring HA for
	# dispatchers.
	# The virtual replicas for resources are placed on different pods by the Eventing scheduler, by having
	# DISPATCHERS_MIN_REPLICAS be more than 1, even when the total number of virtual replicas is less than
	# POD_CAPACITY, the virtual replicas for resources will spread out across replicas leading to better
	# availability.
	- name: DISPATCHERS_MIN_REPLICAS
	value: '0'

However, you may want to have more consumers created within the dispatcher as well, in which case setting

eventing-kafka-broker/control-plane/config/eventing-kafka-broker/200-controller/100-config-kafka-autoscaler.yaml

Line 24 in 0dd0a03

min-scale: "0"

may be useful.

In general, the number of replicas is max(min_replicas, # of consumers / pod_capacity)