Set client.rack based on topology zone

[joke]

Problem

Kafka is rack aware. Clients should specify the client.rack. Brockers should specify broker.rack.

AWS sets broker.rack to the availability zone. Knative could set the client.rack to node label topology.kubernetes.io/zone.

Using rack awareness would reduce cross availability zone traffic costs.

Persona:

System Operator

Exit Criteria

Consumers do set the client.rack based on the topology.kubernetes.io/zone.

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[Cali0707]

/remove-lifecycle stale

@pierDipi this seems like a reasonable request, can we discuss design this week on the Eventing call?

[Cali0707]

It seems like Strimzi makes this configurable through a spec like:

kafka:
  rack
    topologyKey: topology.kubernetes.io/zone

IMO, a flag like kafka-rack-topology-key in the config-kafka-features configmap could make sense here. If present, we could check if there is a label on the node for that, and if there we can use the value to set client.rack

[joke]

Maybe the kafka-rack-topology-key be set to topology.kubernetes.io/zone. After all that's the default annotation.

[pierDipi]

We need to use something like this

      containers:
      - name: ...
        image: ...
        env:
        - name: CLIENT_RACK
          valueFrom:
            fieldRef:
              fieldPath: metadata.labels['topology.kubernetes.io/zone']

and then set in when we read the producer / consumer configurations in (Main.java for receiver and dispatcher)

We need to figure out what happen when that key doesn't exists and if it doesn't work, maybe we support injecting that env variable but we don't set it by default

[pierDipi]

/help

[knative-prow]

@pierDipi:
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If this request no longer meets these requirements, the label can be removed
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In response to this:

/help

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes-sigs/prow repository.

[pierDipi]

/triage accepted

[joke]

We need to use something like this

      containers:
      - name: ...
        image: ...
        env:
        - name: CLIENT_RACK
          valueFrom:
            fieldRef:
              fieldPath: metadata.labels['topology.kubernetes.io/zone']

and then set in when we read the producer / consumer configurations in (Main.java for receiver and dispatcher)

We need to figure out what happen when that key doesn't exists and if it doesn't work, maybe we support injecting that env variable but we don't set it by default

As far as I know the topology.kubernetes.io/zone are only available on the nodes. They are not automatically set on the pod. Thus using a fieldRef will not be working.

The nodeName on the other hand can be injected as an environment variable. That could be used during startup to query the Kubernetes API to obtain the node information.