Add Zookeeper Ops Docs (restart, version-upgrade)

docs/examples/zookeeper/restart/ops.yaml

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+apiVersion: ops.kubedb.com/v1alpha1
+kind: ZooKeeperOpsRequest
+metadata:
+  name: zk-restart
+  namespace: demo
+spec:
+  type: Restart
+  databaseRef:
+    name: zk-quickstart
+  timeout: 3m
+  apply: Always

docs/examples/zookeeper/restart/zookeeper.yaml

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+apiVersion: kubedb.com/v1alpha2
+kind: ZooKeeper
+metadata:
+  name: zk-quickstart
+  namespace: demo
+spec:
+  version: "3.8.3"
+  adminServerPort: 8080
+  replicas: 3
+  storage:
+    resources:
+      requests:
+        storage: "1Gi"
+    storageClassName: "standard"
+    accessModes:
+      - ReadWriteOnce
+  deletionPolicy: "WipeOut"

docs/examples/zookeeper/update-version/zk-version-upgrade-ops.yaml

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+apiVersion: ops.kubedb.com/v1alpha1
+kind: ZooKeeperOpsRequest
+metadata:
+  name: upgrade-topology
+  namespace: demo
+spec:
+  databaseRef:
+    name: zk-quickstart
+  type: UpdateVersion
+  updateVersion:
+    targetVersion: 3.9.1
+  timeout: 5m
+  apply: IfReady

docs/examples/zookeeper/update-version/zookeeper.yaml

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+apiVersion: kubedb.com/v1alpha2
+kind: ZooKeeper
+metadata:
+  name: zk-quickstart
+  namespace: demo
+spec:
+  version: "3.8.3"
+  adminServerPort: 8080
+  replicas: 3
+  storage:
+    resources:
+      requests:
+        storage: "1Gi"
+    storageClassName: "standard"
+    accessModes:
+      - ReadWriteOnce
+  deletionPolicy: "WipeOut"

docs/guides/zookeeper/restart/_index.md

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+---
+title: Restart ZooKeeper
+menu:
+  docs_{{ .version }}:
+    identifier: zk-restart
+    name: Restart
+    parent: zk-zookeeper-guides
+    weight: 100
+menu_name: docs_{{ .version }}
+---

docs/guides/zookeeper/restart/restart.md

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+---
+title: Restart ZooKeeper
+menu:
+  docs_{{ .version }}:
+    identifier: zk-restart-details
+    name: Restart Cluster
+    parent: zk-restart
+    weight: 10
+menu_name: docs_{{ .version }}
+section_menu_id: guides
+---
+
+> New to KubeDB? Please start [here](/docs/README.md).
+
+# Restart ZooKeeper
+
+KubeDB supports restarting the ZooKeeper database via a ZooKeeperOpsRequest. Restarting is useful if some pods are got stuck in some phase, or they are not working correctly. This tutorial will show you how to use that.
+
+## Before You Begin
+
+- At first, you need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with your cluster. If you do not already have a cluster, you can create one by using [kind](https://kind.sigs.k8s.io/docs/user/quick-start/).
+
+- Now, install KubeDB cli on your workstation and KubeDB operator in your cluster following the steps [here](/docs/setup/README.md).
+
+- To keep things isolated, this tutorial uses a separate namespace called `demo` throughout this tutorial.
+
+```bash
+  $ kubectl create ns demo
+  namespace/demo created
+  ```
+
+> Note: YAML files used in this tutorial are stored in [docs/examples/zookeeper](https://github.com/kubedb/docs/tree/{{< param "info.version" >}}/docs/examples/zookeeper) folder in GitHub repository [kubedb/docs](https://github.com/kubedb/docs).
+
+## Deploy ZooKeeper
+
+In this section, we are going to deploy a ZooKeeper database using KubeDB.
+
+```yaml
+apiVersion: kubedb.com/v1alpha2
+kind: ZooKeeper
+metadata:
+  name: zk-quickstart
+  namespace: demo
+spec:
+  version: "3.8.3"
+  adminServerPort: 8080
+  replicas: 3
+  storage:
+    resources:
+      requests:
+        storage: "1Gi"
+    storageClassName: "standard"
+    accessModes:
+      - ReadWriteOnce
+  deletionPolicy: "WipeOut"
+
+```
+
+Let's create the `ZooKeeper` CR we have shown above,
+
+```bash
+$ kubectl create -f https://github.com/kubedb/docs/raw/{{< param "info.version" >}}/docs/examples/zookeeper/restart/zookeeper.yaml
+zookeeper.kubedb.com/zk-quickstart created
+```
+
+## Apply Restart opsRequest
+
+```yaml
+apiVersion: ops.kubedb.com/v1alpha1
+kind: ZooKeeperOpsRequest
+metadata:
+  name: zk-restart
+  namespace: demo
+spec:
+  type: Restart
+  databaseRef:
+    name: zk-quickstart
+  timeout: 3m
+  apply: Always
+```
+
+- `spec.type` specifies the Type of the ops Request
+- `spec.databaseRef` holds the name of the ZooKeeper database.  The db should be available in the same namespace as the opsRequest
+- The meaning of `spec.timeout` & `spec.apply` fields will be found [here](/docs/guides/zookeeper/concepts/opsrequest.md#spectimeout)
+
+> Note: The method of restarting the standalone & clustered zookeeper is exactly same as above. All you need, is to specify the corresponding ZooKeeper name in `spec.databaseRef.name` section.
+
+Let's create the `ZooKeeperOpsRequest` CR we have shown above,
+
+```bash
+$ kubectl create -f https://github.com/kubedb/docs/raw/{{< param "info.version" >}}/docs/examples/zookeeper/restart/ops.yaml
+zookeeperopsrequest.ops.kubedb.com/zk-restart created
+```
+
+Now the Ops-manager operator will restart the pods sequentially by their cardinal suffix.
+
+```shell
+$ kubectl get zookeeperopsrequest -n demo
+NAME      TYPE      STATUS       AGE
+restart   Restart   Successful   10m
+
+$ kubectl get zookeeperopsrequest -n demo -oyaml zk-restart
+apiVersion: ops.kubedb.com/v1alpha1
+kind: ZooKeeperOpsRequest
+metadata:
+  annotations:
+    kubectl.kubernetes.io/last-applied-configuration: |
+      {"apiVersion":"ops.kubedb.com/v1alpha1","kind":"ZooKeeperOpsRequest","metadata":{"annotations":{},"name":"zk-restart","namespace":"demo"},"spec":{"apply":"Always","databaseRef":{"name":"zk-quickstart"},"timeout":"3m","type":"Restart"}}
+  creationTimestamp: "2024-10-22T09:22:57Z"
+  generation: 1
+  name: zk-restart
+  namespace: demo
+  resourceVersion: "1072309"
+  uid: 6091d9fa-1c2b-4734-bdd1-1ace91460bea
+spec:
+  apply: Always
+  databaseRef:
+    name: zk-quickstart
+  timeout: 3m
+  type: Restart
+status:
+  conditions:
+  - lastTransitionTime: "2024-10-22T09:22:57Z"
+    message: ZooKeeper ops-request has started to restart zookeeper nodes
+    observedGeneration: 1
+    reason: Restart
+    status: "True"
+    type: Restart
+  - lastTransitionTime: "2024-10-22T09:25:45Z"
+    message: Successfully Restarted ZooKeeper nodes
+    observedGeneration: 1
+    reason: RestartNodes
+    status: "True"
+    type: RestartNodes
+  - lastTransitionTime: "2024-10-22T09:23:05Z"
+    message: get pod; ConditionStatus:True; PodName:zk-quickstart-0
+    observedGeneration: 1
+    status: "True"
+    type: GetPod--zk-quickstart-0
+  - lastTransitionTime: "2024-10-22T09:23:05Z"
+    message: evict pod; ConditionStatus:True; PodName:zk-quickstart-0
+    observedGeneration: 1
+    status: "True"
+    type: EvictPod--zk-quickstart-0
+  - lastTransitionTime: "2024-10-22T09:23:10Z"
+    message: running pod; ConditionStatus:False
+    observedGeneration: 1
+    status: "False"
+    type: RunningPod
+  - lastTransitionTime: "2024-10-22T09:23:45Z"
+    message: get pod; ConditionStatus:True; PodName:zk-quickstart-1
+    observedGeneration: 1
+    status: "True"
+    type: GetPod--zk-quickstart-1
+  - lastTransitionTime: "2024-10-22T09:23:45Z"
+    message: evict pod; ConditionStatus:True; PodName:zk-quickstart-1
+    observedGeneration: 1
+    status: "True"
+    type: EvictPod--zk-quickstart-1
+  - lastTransitionTime: "2024-10-22T09:24:25Z"
+    message: get pod; ConditionStatus:True; PodName:zk-quickstart-2
+    observedGeneration: 1
+    status: "True"
+    type: GetPod--zk-quickstart-2
+  - lastTransitionTime: "2024-10-22T09:24:25Z"
+    message: evict pod; ConditionStatus:True; PodName:zk-quickstart-2
+    observedGeneration: 1
+    status: "True"
+    type: EvictPod--zk-quickstart-2
+  - lastTransitionTime: "2024-10-22T09:25:05Z"
+    message: get pod; ConditionStatus:True; PodName:zk-quickstart-3
+    observedGeneration: 1
+    status: "True"
+    type: GetPod--zk-quickstart-3
+  - lastTransitionTime: "2024-10-22T09:25:05Z"
+    message: evict pod; ConditionStatus:True; PodName:zk-quickstart-3
+    observedGeneration: 1
+    status: "True"
+    type: EvictPod--zk-quickstart-3
+  - lastTransitionTime: "2024-10-22T09:25:45Z"
+    message: Controller has successfully restart the ZooKeeper replicas
+    observedGeneration: 1
+    reason: Successful
+    status: "True"
+    type: Successful
+  observedGeneration: 1
+  phase: Successful
+
+```
+
+
+## Cleaning up
+
+To cleanup the Kubernetes resources created by this tutorial, run:
+
+```bash
+kubectl delete zookeeperopsrequest -n demo zk-restart
+kubectl delete zookeeper -n demo zk-quickstart
+kubectl delete ns demo
+```
+
+## Next Steps
+
+- Detail concepts of [ZooKeeper object](/docs/guides/zookeeper/concepts/zookeeper.md).
+- Monitor your ZooKeeper database with KubeDB using [out-of-the-box Prometheus operator](/docs/guides/zookeeper/monitoring/using-prometheus-operator.md).
+- Monitor your ZooKeeper database with KubeDB using [out-of-the-box builtin-Prometheus](/docs/guides/zookeeper/monitoring/using-builtin-prometheus.md).
+- Detail concepts of [ZooKeeper object](/docs/guides/zookeeper/concepts/zookeeper.md).
+- Want to hack on KubeDB? Check our [contribution guidelines](/docs/CONTRIBUTING.md).

docs/guides/zookeeper/update-version/_index.md

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+---
+title: Updating ZooKeeper
+menu:
+  docs_{{ .version }}:
+    identifier: zk-update-version
+    name: Update Version
+    parent: zk-zookeeper-guides
+    weight: 50
+menu_name: docs_{{ .version }}
+---

docs/guides/zookeeper/update-version/overview.md

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+---
+title: Updating ZooKeeper Overview
+menu:
+  docs_{{ .version }}:
+    identifier: zk-update-version-overview
+    name: Overview
+    parent: zk-update-version
+    weight: 10
+menu_name: docs_{{ .version }}
+section_menu_id: guides
+---
+
+> New to KubeDB? Please start [here](/docs/README.md).
+
+# updating ZooKeeper version Overview
+
+This guide will give you an overview on how KubeDB Ops-manager operator update the version of `ZooKeeper` database.
+
+## Before You Begin
+
+- You should be familiar with the following `KubeDB` concepts:
+    - [ZooKeeper](/docs/guides/zookeeper/concepts/zookeeper.md)
+    - [ZooKeeperOpsRequest](/docs/guides/zookeeper/concepts/opsrequest.md)
+
+## How update version Process Works
+
+The following diagram shows how KubeDB Ops-manager operator used to update the version of `ZooKeeper`. Open the image in a new tab to see the enlarged version.
+
+<figure align="center">
+  <img alt="updating Process of ZooKeeper" src="/docs/images/day-2-operation/zookeeper/zk-version-update.svg">
+<figcaption align="center">Fig: updating Process of ZooKeeper</figcaption>
+</figure>
+
+The updating process consists of the following steps:
+
+1. At first, a user creates a `ZooKeeper` Custom Resource (CR).
+
+2. `KubeDB` Provisioner  operator watches the `ZooKeeper` CR.
+
+3. When the operator finds a `ZooKeeper` CR, it creates required number of `PetSets` and other kubernetes native resources like secrets, services, etc.
+
+4. Then, in order to update the version of the `ZooKeeper` database the user creates a `ZooKeeperOpsRequest` CR with the desired version.
+
+5. `KubeDB` Ops-manager operator watches the `ZooKeeperOpsRequest` CR.
+
+6. When it finds a `ZooKeeperOpsRequest` CR, it halts the `ZooKeeper` object which is referred from the `ZooKeeperOpsRequest`. So, the `KubeDB` Provisioner  operator doesn't perform any operations on the `ZooKeeper` object during the updating process.
+
+7. By looking at the target version from `ZooKeeperOpsRequest` CR, `KubeDB` Ops-manager operator updates the images of all the `PetSets`. After each image update, the operator performs some checks such as if the oplog is synced and database size is almost same or not.
+
+8. After successfully updating the `PetSets` and their `Pods` images, the `KubeDB` Ops-manager operator updates the image of the `ZooKeeper` object to reflect the updated state of the database.
+
+9. After successfully updating of `ZooKeeper` object, the `KubeDB` Ops-manager operator resumes the `ZooKeeper` object so that the `KubeDB` Provisioner  operator can resume its usual operations.
+
+In the next doc, we are going to show a step-by-step guide on updating of a ZooKeeper database using updateVersion operation.