ZooKeeper is a centralized service for maintaining configuration information, naming, providing distributed synchronization, and providing group services.
Using Ondat persistent volumes with Apache Zookeeper means that if a pod fails, the cluster is only in a degraded state for as long as it takes Kubernetes to restart the pod. When the pod comes back up, the pod data is immediately available. Should Kubernetes schedule the Zookeeper pod on a new node, Ondat allows for the data to be available to the pod, irrespective of whether or not the original Ondat master volume is located on the same node.
As Zookeeper has features to allow it to handle replication, and as such careful consideration of whether to allow Ondat or Zookeeper to handle replication is required.
Before you start, ensure you have Ondat installed and ready on a Kubernetes cluster. See our guide on how to install Ondat on Kubernetes for more information.
Deploying Zookeeper on Kubernetes
- Ondat is assumed to have been installed; check for the latest available version here.
To simplify the deployment of Zookeeper, we’ve used this Zookeeper helm chart
1.2.2, app version
3.4.10) and rendered it into the example
deployment files you can find in our GitHub
Clone the use cases repository
You can find the latest files in the Ondat use cases repository in
git clone https://github.com/storageos/use-cases.git storageos-usecases
--- apiVersion: apps/v1beta1 kind: StatefulSet metadata: name: zookeeper ... spec: replicas: 3 # <--- number of zookeeper pods ... containers: - name: zookeeper image: "gcr.io/google_samples/k8szk:v3" imagePullPolicy: IfNotPresent ... volumeMounts: - name: data mountPath: /var/lib/zookeeper volumeClaimTemplates: - metadata: name: data spec: accessModes: - "ReadWriteOnce" storageClassName: "storageos" # <--- the StorageClass to use resources: requests: storage: "5Gi" # <--- storage requested per pod
This excerpt is from the StatefulSet definition (
The file contains the PersistentVolumeClaim template that will dynamically
provision the necessary storage, using the Ondat storage class. Dynamic
provisioning occurs as a volumeMount has been declared with the same name
as a VolumeClaimTemplate.
Create the kubernetes objects
cd storageos-usecases kubectl apply -f ./zookeeper/
Confirm Zookeeper is up and running
$ kubectl get pods NAME READY STATUS RESTARTS AGE zookeeper-0 1/1 Running 0 2m30s zookeeper-1 1/1 Running 0 112s zookeeper-2 1/1 Running 0 56s zookeeper-test-client 1/1 Running 0 2m30s
Connect to Zookeeper
Connect to the zookeeper client pod and list existing topics using the service endpoint
kubectl exec -it zookeeper-test-client /bin/bash
and issue a command to the zookeeper service
zkCli.sh -server zookeeper ls /zookeeper