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Running simple kafka instance on kubernetes

8/31/2020

I am new to the Kubernetes and trying to deploy a single replica kafka instance on the single node minikube cluster.

Here is the zookeeper service/deployment yml

apiVersion: v1
kind: Service
metadata:
  name: zookeeper-cluster
  labels:
    component: zookeeper
spec:
  ports:
  - name: "2181"
    port: 2181
    targetPort: 2181
  selector:
    component: zookeeper
status:
  loadBalancer: {}

---

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    component: zookeeper
  name: zookeeper
spec:
  replicas: 1
  strategy:
    type: Recreate
  selector:
    matchLabels:
      component: zookeeper      
  template:
    metadata:
      labels:
        component: zookeeper
    spec:
      containers:
      - image: zookeeper:3.4.13
        name: zookeeper
        ports:
        - containerPort: 2181
        resources:
          limits:
            memory: "256Mi"
            cpu: "100m"
        volumeMounts:
        - mountPath: /conf
          name: zookeeper-claim0
        - mountPath: /data
          name: zookeeper-claim1
        - mountPath: /datalog
          name: zookeeper-claim2
      restartPolicy: Always
      volumes:
      - name: zookeeper-claim0
        persistentVolumeClaim:
          claimName: zookeeper-claim0
      - name: zookeeper-claim1
        persistentVolumeClaim:
          claimName: zookeeper-claim1
      - name: zookeeper-claim2
        persistentVolumeClaim:
          claimName: zookeeper-claim2
status: {}

and here is the Kafka service/deployment yml

apiVersion: v1
kind: Service
metadata:
  name: kafka-cluster
  labels:
    component: kafka
spec:
  ports:
  - name: "9092"
    port: 9092
    targetPort: 9092
  selector:
    component: kafka
status:
  loadBalancer: {}

---

apiVersion: apps/v1
kind: Deployment
metadata:
  labels:
    component: kafka
  name: kafka
spec:
  replicas: 1
  strategy:
    type: Recreate
  selector:
    matchLabels:
      component: kafka    
  template:
    metadata:
      labels:
        component: kafka
    spec:
      containers:
      - args:
        - start-kafka.sh
        env:
        - name: KAFKA_INTER_BROKER_LISTENER_NAME
          value: LISTENER_BOB
        - name: KAFKA_ADVERTISED_LISTENERS
          value: LISTENER_BOB://:9092
        - name: KAFKA_LISTENERS
          value: LISTENER_BOB://:9092
        - name: KAFKA_LISTENER_SECURITY_PROTOCOL_MAP
          value:  LISTENER_BOB:PLAINTEXT
        - name: KAFKA_BROKER_ID
          value: "1"
        - name: KAFKA_LOG_DIRS
          value: /kafka/kafka-logs
        - name: KAFKA_ZOOKEEPER_CONNECT
          value: zookeeper-cluster:2181
        image: wurstmeister/kafka:2.12-2.4.1
        name: kafka
        ports:
        - containerPort: 9092
        resources:
          limits:
            memory: "256Mi"
            cpu: "200m"
        volumeMounts:
        - mountPath: /kafka/kafka-logs
          name: kafka-claim0
      restartPolicy: Always
      volumes:
      - name: kafka-claim0
        persistentVolumeClaim:
          claimName: kafka-claim0
status: {}

When trying to access the kafka from another application on kafka-cluster:9092, which is also running as a deployment, it throws an UnresolvedAddressException. where kafka-6799c65d58-f6tbt:9092 is the pod name

java.io.IOException: Can't resolve address: **kafka-6799c65d58-f6tbt:9092**
	at org.apache.kafka.common.network.Selector.doConnect(Selector.java:235)
	at org.apache.kafka.common.network.Selector.connect(Selector.java:214)
	at org.apache.kafka.clients.NetworkClient.initiateConnect(NetworkClient.java:864)
	at org.apache.kafka.clients.NetworkClient.access$700(NetworkClient.java:64)
	at org.apache.kafka.clients.NetworkClient$DefaultMetadataUpdater.maybeUpdate(NetworkClient.java:1035)
	at org.apache.kafka.clients.NetworkClient$DefaultMetadataUpdater.maybeUpdate(NetworkClient.java:920)
	at org.apache.kafka.clients.NetworkClient.poll(NetworkClient.java:508)
	at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:239)
	at org.apache.kafka.clients.producer.internals.Sender.run(Sender.java:163)
	at java.base/java.lang.Thread.run(Thread.java:835)
Caused by: java.nio.channels.UnresolvedAddressException: null
	at java.base/sun.nio.ch.Net.checkAddress(Net.java:130)
	at java.base/sun.nio.ch.SocketChannelImpl.connect(SocketChannelImpl.java:675)
	at org.apache.kafka.common.network.Selector.doConnect(Selector.java:233)
	... 9 common frames omitted

Am I making any mistake while configuring it? or is there any alternative to it?

-- Nishit Jain

apache-kafka

kubernetes

kubernetes-pod

2 Answers

8/31/2020

There are a couple of problems that I can think of.

The service type has not been explicitly set thus, defaults to ClusterIP type which is only accessible within the cluster. (K8s Internal DNS should work) . You can use NodePort or LoadBalancer types if you want to expose it to the outside world.
Even if your application is running on the same k8s cluster and in a different k8s namespace, then you have to use kafka-cluster.mynamespace as the internal address.

Check here for more info: https://kubernetes.io/docs/concepts/services-networking/

-- Pubudu Sitinamaluwa

Source: StackOverflow

9/1/2020

It looks like kafka broker is advertising its own hostname (kafka-6799c65d58-f6tbt) as FQDN, which is the same as a pod name. Deployment pod's names cannot be resolved by DNS.

If you take a look at any kafka helm chart i.e. this one you are going to see that they are using statefulsets. Statefulsets allow for resolving ip addresses of pods. Take a look here at k8s docs on how this works.

You could also try setting KAFKA_ADVERTISED_LISTENERS to :

- name: MY_POD_IP
  valueFrom:
    fieldRef:
      fieldPath: status.podIP
- name: KAFKA_ADVERTISED_LISTENERS
  value: "LISTENER_BOB://$(MY_POD_IP):9092/"

But it doesn't scale well when changeing number of replicas.

-- Matt

Source: StackOverflow

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Running simple kafka instance on kubernetes

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