Deploying

$ juju add-model myzookeeper
$ juju deploy zookeeper-k8s -n 3

Where:

• zookeeper-k8s: the name of this Charmed Operator on the Charmhub.
• -n: the number of Juju units to deploy, i.e. the number of wanted k8s pods. Any number >= 1 is supported but for production you should pick an odd number >= 3.

Inspecting/Operating

The deployment can be inspected with juju and kubectl:

$ juju status
Model        Controller  Cloud/Region        Version  SLA          Timestamp
myzookeeper  micro       microk8s/localhost  2.9.0    unsupported  12:27:29Z

App            Version  Status  Scale  Charm          Store     Channel  Rev  OS          Address  Message
zookeeper-k8s           active      3  zookeeper-k8s  charmhub  stable     4  kubernetes

Unit              Workload  Agent  Address    Ports  Message
zookeeper-k8s/0   active    idle   10.1.0.47
zookeeper-k8s/1*  active    idle   10.1.0.49
zookeeper-k8s/2   active    idle   10.1.0.48

$ juju config zookeeper-k8s client-port
2181

$ kubectl get pods --namespace=myzookeeper
NAME                             READY   STATUS    RESTARTS   AGE
modeloperator-75988dd959-vvh2t   1/1     Running   0          4m33s
zookeeper-k8s-2                  2/2     Running   0          92s
zookeeper-k8s-1                  2/2     Running   0          92s
zookeeper-k8s-0                  2/2     Running   0          92s

This teaches us the IP addresses (here 10.1.0.47-49) and the TCP port (2181) to be used in order to access the ZooKeeper data from any client.

ZooKeeper can be seeded with some dummy data:

$ juju run-action zookeeper-k8s/0 seed-data --wait

This data should then be replicated accross the entire ZooKeeper cluster and all units should present that same data:

$ juju run-action zookeeper-k8s/0 zookeeper-k8s/1 zookeeper-k8s/2 dump-data --wait
unit-zookeeper-k8s-0:
  UnitId: zookeeper-k8s/0
  id: "8"
  results:
    content: '{''test-seed'': {''my-first-key'': b''my first value'', ''my-second-key'':
      b''my second value''}, ''zookeeper'': {''config'': b''server.1=10.1.0.47:2888:3888:participant\nserver.2=10.1.0.48:2888:3888:participant\nserver.3=10.1.0.49:2888:3888:participant\nversion=0'',
      ''quota'': b''''}}'
  status: completed
  timing:
    completed: 2021-06-02 11:41:36 +0000 UTC
    enqueued: 2021-06-02 11:41:33 +0000 UTC
    started: 2021-06-02 11:41:35 +0000 UTC
unit-zookeeper-k8s-1:
  UnitId: zookeeper-k8s/1
  id: "9"
  results:
    content: '{''test-seed'': {''my-first-key'': b''my first value'', ''my-second-key'':
      b''my second value''}, ''zookeeper'': {''config'': b''server.1=10.1.0.47:2888:3888:participant\nserver.2=10.1.0.48:2888:3888:participant\nserver.3=10.1.0.49:2888:3888:participant\nversion=0'',
      ''quota'': b''''}}'
  status: completed
  timing:
    completed: 2021-06-02 11:41:36 +0000 UTC
    enqueued: 2021-06-02 11:41:33 +0000 UTC
    started: 2021-06-02 11:41:35 +0000 UTC
unit-zookeeper-k8s-2:
  UnitId: zookeeper-k8s/2
  id: "10"
  results:
    content: '{''test-seed'': {''my-first-key'': b''my first value'', ''my-second-key'':
      b''my second value''}, ''zookeeper'': {''config'': b''server.1=10.1.0.47:2888:3888:participant\nserver.2=10.1.0.48:2888:3888:participant\nserver.3=10.1.0.49:2888:3888:participant\nversion=0'',
      ''quota'': b''''}}'
  status: completed
  timing:
    completed: 2021-06-02 11:41:36 +0000 UTC
    enqueued: 2021-06-02 11:41:33 +0000 UTC
    started: 2021-06-02 11:41:35 +0000 UTC

Any ZooKeeper client can be used to read and write data to/from the deployed ZooKeeper cluster, e.g. ZooNavigator:

$ sudo snap install zoonavigator  # ZooNavigator's Web-UI is then served at:
$ firefox http://localhost:9000

Relating

Other Charmed Operators can be related to this one if they require a ZooKeeper database. The zookeeper-dummy-client-k8s is an example:

$ juju add-model myzookeeper
$ juju deploy zookeeper-k8s -n 3
$ juju deploy zookeeper-dummy-client-k8s
$ juju add-relation zookeeper-k8s:client zookeeper-dummy-client-k8s:zookeeper

See how to implement such a Charmed Operator.