ZooKeeper

Apache ZooKeeper provides distributed coordination for cloud applications. The HelmForge chart deploys the official ZooKeeper image as a stable StatefulSet ensemble with quorum-safe defaults.

Key Features

Official docker.io/library/zookeeper image pinned to 3.9.5
Three-node replicated ensemble by default
Validation against accidental even replica counts
Client, headless, secure client, and metrics Services
Optional SASL/Digest client authentication
Optional secure client port using existing JKS keystore and truststore Secrets
Prometheus metrics provider, ServiceMonitor, PrometheusRule, NetworkPolicy, PDB, External Secrets, and dual-stack Services

Installation

helm repo add helmforge https://repo.helmforge.dev
helm repo update
helm install zookeeper helmforge/zookeeper --namespace zookeeper --create-namespace

helm install zookeeper oci://ghcr.io/helmforgedev/helm/zookeeper --namespace zookeeper --create-namespace

Examples

Standalone local install:

replicaCount: 1
persistence:
  enabled: false

Production ensemble:

replicaCount: 3
persistence:
  enabled: true
  size: 20Gi
podDisruptionBudget:
  enabled: true
  maxUnavailable: 1
metrics:
  enabled: true
  serviceMonitor:
    enabled: true

Operations

Keep production replica counts odd. Use allowEvenReplicas=true only for a deliberate platform-specific reason. Enable NetworkPolicy and explicitly allow client, quorum, DNS, and metrics flows.

Architecture

ZooKeeper is deployed as a StatefulSet with stable pod DNS, a client Service, a headless Service for quorum traffic, and optional metrics exposure. Production ensembles should use an odd replica count so quorum can survive a member failure.

Ports and roles:

client port for application connections
quorum election and follower communication ports between pods
optional secure client port when TLS is enabled
optional metrics port for Prometheus scraping

The chart blocks accidental even replica counts by default. Set allowEvenReplicas=true only when an operator has a clear reason and accepts the quorum tradeoff.

Production Values

Use three replicas, persistent data, a data log volume, PDB, metrics, topology spread, and NetworkPolicy:

replicaCount: 3

persistence:
  enabled: true
  size: 20Gi
  dataLogDir:
    enabled: true
    size: 10Gi

resources:
  requests:
    cpu: 500m
    memory: 1Gi
  limits:
    memory: 2Gi

podDisruptionBudget:
  enabled: true
  maxUnavailable: 1

networkPolicy:
  enabled: true

metrics:
  enabled: true
  serviceMonitor:
    enabled: true
  prometheusRule:
    enabled: true

For local or CI smoke tests, standalone mode is intentionally simple:

replicaCount: 1

persistence:
  enabled: false

Authentication

Client SASL/Digest authentication is optional:

auth:
  client:
    enabled: true
    existingSecret: zookeeper-client-auth
    usernameKey: username
    passwordKey: password

When clients use authentication, update every application connection string and client JAAS configuration before enforcing the authenticated path.

TLS

Secure client port support expects existing JKS keystore and truststore material:

tls:
  client:
    enabled: true
    existingSecret: zookeeper-client-tls
    keystoreKey: keystore.jks
    truststoreKey: truststore.jks
    existingPasswordsSecret: zookeeper-client-tls-passwords

TLS changes affect both server startup and client compatibility. Validate the exact client libraries used by Kafka, Solr, or other ZooKeeper consumers before rollout.

External Secrets

External Secrets Operator can reconcile auth and TLS material when the operator already exists:

externalSecrets:
  enabled: true
  secretStoreRef:
    name: cluster-secrets
    kind: ClusterSecretStore
  data:
    - secretKey: password
      remoteRef:
        key: zookeeper/client
        property: password

The chart renders ExternalSecret resources only when explicitly enabled; it does not install External Secrets Operator or create a SecretStore.

Networking

NetworkPolicy must allow:

client traffic from approved application namespaces
quorum traffic between ZooKeeper pods
DNS egress
metrics scraping from the monitoring namespace when metrics are enabled

Dual-stack Service fields are available:

service:
  ipFamilyPolicy: PreferDualStack
  ipFamilies:
    - IPv4
    - IPv6

Observability

Enable metrics, ServiceMonitor, and PrometheusRule together when Prometheus Operator is available:

metrics:
  enabled: true
  serviceMonitor:
    enabled: true
    additionalLabels:
      release: prometheus
  prometheusRule:
    enabled: true

Watch quorum health, outstanding requests, latency, watches, open file descriptors, leader changes, and pod restarts.

Validation

After deployment:

helm test zookeeper -n zookeeper
kubectl get pods -n zookeeper -l app.kubernetes.io/name=zookeeper
kubectl logs -n zookeeper statefulset/zookeeper --since=10m
kubectl get events -n zookeeper --sort-by=.lastTimestamp

For production, validate a real client connection, quorum after a pod restart, and behavior during voluntary disruption with the PDB enabled.

Common Issues

Symptom	Likely Cause	Fix
Render blocks even replicas	Quorum safety validation	Use an odd replica count or deliberately set `allowEvenReplicas=true`.
Ensemble never forms quorum	Pod DNS, NetworkPolicy, or quorum ports blocked	Check headless Service DNS and intra-ensemble policy.
Clients fail after enabling auth	Client JAAS/config not updated	Roll client configuration before enforcing auth.
TLS startup fails	JKS Secret keys or passwords mismatch	Verify Secret keys and password Secret values.

Values

Parameter	Default	Description
`replicaCount`	`3`	ZooKeeper ensemble size.
`allowEvenReplicas`	`false`	Allow even replica counts.
`image.repository`	`docker.io/library/zookeeper`	Official ZooKeeper image.
`zookeeper.clientPort`	`2181`	Plain client port.
`auth.client.enabled`	`false`	Enable SASL/Digest client authentication.
`tls.client.enabled`	`false`	Enable secure client port with existing JKS material.
`persistence.enabled`	`true`	Persist ZooKeeper data.
`metrics.enabled`	`false`	Enable Prometheus metrics provider.
`podDisruptionBudget.enabled`	`true`	Render PDB for ensemble availability.
`externalSecrets.enabled`	`false`	Render ExternalSecret resources.