Deploying Apache Zookeeper on Kubernetes with StatefulSet, Operator, and KUDO

With the rise of cloud‑native trends, foundational components such as Apache Zookeeper need to run on Kubernetes. Zookeeper serves as a registration center in micro‑service architectures.

Running a Zookeeper cluster on Kubernetes brings elasticity, scaling and high‑availability.

Deploy Zookeeper with a StatefulSet

The official method creates a headless service, a cluster service, a PodDisruptionBudget and a StatefulSet.

apiVersion: v1
kind: Service
metadata:
  name: zk-hs
  labels:
    app: zk
spec:
  ports:
  - port: 2888
    name: server
  - port: 3888
    name: leader-election
  clusterIP: None
  selector:
    app: zk
---
apiVersion: v1
kind: Service
metadata:
  name: zk-cs
  labels:
    app: zk
spec:
  ports:
  - port: 2181
    name: client
  selector:
    app: zk
---
apiVersion: policy/v1beta1
kind: PodDisruptionBudget
metadata:
  name: zk-pdb
spec:
  selector:
    matchLabels:
      app: zk
  maxUnavailable: 1
---
apiVersion: apps/v1
kind: StatefulSet
metadata:
  name: zk
spec:
  selector:
    matchLabels:
      app: zk
  serviceName: zk-hs
  replicas: 3
  updateStrategy:
    type: RollingUpdate
  podManagementPolicy: OrderedReady
  template:
    metadata:
      labels:
        app: zk
    spec:
      affinity:
        podAntiAffinity:
          requiredDuringSchedulingIgnoredDuringExecution:
          - labelSelector:
              matchExpressions:
              - key: "app"
                operator: In
                values:
                - zk
            topologyKey: "kubernetes.io/hostname"
      containers:
      - name: kubernetes-zookeeper
        imagePullPolicy: Always
        image: "k8s.gcr.io/kubernetes-zookeeper:1.0-3.4.10"
        resources:
          requests:
            memory: "1Gi"
            cpu: "0.5"
        ports:
        - containerPort: 2181
          name: client
        - containerPort: 2888
          name: server
        - containerPort: 3888
          name: leader-election
        command:
        - sh
        - -c
        - "start-zookeeper \
          --servers=3 \
          --data_dir=/var/lib/zookeeper/data \
          --data_log_dir=/var/lib/zookeeper/data/log \
          --conf_dir=/opt/zookeeper/conf \
          --client_port=2181 \
          --election_port=3888 \
          --server_port=2888 \
          --tick_time=2000 \
          --init_limit=10 \
          --sync_limit=5 \
          --heap=512M \
          --max_client_cnxns=60 \
          --snap_retain_count=3 \
          --purge_interval=12 \
          --max_session_timeout=40000 \
          --min_session_timeout=4000 \
          --log_level=INFO"
        readinessProbe:
          exec:
            command:
            - sh
            - -c
            - "zookeeper-ready 2181"
          initialDelaySeconds: 10
          timeoutSeconds: 5
        livenessProbe:
          exec:
            command:
            - sh
            - -c
            - "zookeeper-ready 2181"
          initialDelaySeconds: 10
          timeoutSeconds: 5
        volumeMounts:
        - name: datadir
          mountPath: /var/lib/zookeeper
      securityContext:
        runAsUser: 1000
        fsGroup: 1000
  volumeClaimTemplates:
  - metadata:
      name: datadir
    spec:
      accessModes: ["ReadWriteOnce"]
      resources:
        requests:
          storage: 10Gi

Apply the configuration with kubectl apply and verify the pods and services are created.

Scaling is simple: edit the StatefulSet replica count and adjust the server count, then the rolling update expands the cluster.

Deploy Zookeeper with a Kubernetes Operator

First create the custom resource definition ZookeeperCluster, then set up RBAC, deploy the operator, and create a CR describing the desired Zookeeper cluster.

apiVersion: zookeeper.pravega.io/v1beta1
kind: ZookeeperCluster
metadata:
  name: zookeeper
spec:
  replicas: 3
  image:
    repository: pravega/zookeeper
    tag: 0.2.9
  storageType: persistence
  persistence:
    reclaimPolicy: Delete
    spec:
      storageClassName: "rbd"
      resources:
        requests:
          storage: 8Gi

Apply the CR and the operator creates the Zookeeper pods; scaling is done by patching the CR.

kubectl patch zk zookeeper --type='json' -p='[{"op": "replace", "path": "/spec/replicas", "value":4}]'

Deploy Zookeeper with KUDO

KUDO is a framework for building Kubernetes operators. Install KUDO, initialise it, then install the built‑in Zookeeper operator, specifying a storage class.

brew install kudo
kubectl kudo init
kubectl kudo install zookeeper --instance=zookeeper-instance -p STORAGE_CLASS=rbd

Scaling is performed by updating the instance parameter:

kubectl kudo update --instance=zookeeper-instance -p NODE_COUNT=4