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+# incubator/zookeeper
+
+This helm chart provides an implementation of the ZooKeeper [StatefulSet](http://kubernetes.io/docs/concepts/abstractions/controllers/statefulsets/) found in Kubernetes Contrib [Zookeeper StatefulSet](https://github.com/kubernetes/contrib/tree/master/statefulsets/zookeeper).
+
+## Prerequisites
+* Kubernetes 1.6+
+* PersistentVolume support on the underlying infrastructure
+* A dynamic provisioner for the PersistentVolumes
+* A familiarity with [Apache ZooKeeper 3.4.x](https://zookeeper.apache.org/doc/current/)
+
+## Chart Components
+This chart will do the following:
+
+* Create a fixed size ZooKeeper ensemble using a [StatefulSet](http://kubernetes.io/docs/concepts/abstractions/controllers/statefulsets/).
+* Create a [PodDisruptionBudget](https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-disruption-budget/) so kubectl drain will respect the Quorum size of the ensemble.
+* Create a [Headless Service](https://kubernetes.io/docs/concepts/services-networking/service/) to control the domain of the ZooKeeper ensemble.
+* Create a Service configured to connect to the available ZooKeeper instance on the configured client port.
+* Optionally apply a [Pod Anti-Affinity](https://kubernetes.io/docs/concepts/configuration/assign-pod-node/#inter-pod-affinity-and-anti-affinity-beta-feature) to spread the ZooKeeper ensemble across nodes.
+* Optionally start JMX Exporter and Zookeeper Exporter containers inside Zookeeper pods.
+* Optionally create a job which creates Zookeeper chroots (e.g. `/kafka1`).
+
+## Installing the Chart
+You can install the chart with the release name `zookeeper` as below.
+
+```console
+$ helm repo add incubator http://storage.googleapis.com/kubernetes-charts-incubator
+$ helm install --name zookeeper incubator/zookeeper
+```
+
+If you do not specify a name, helm will select a name for you.
+
+### Installed Components
+You can use `kubectl get` to view all of the installed components.
+
+```console{%raw}
+$ kubectl get all -l app=zookeeper
+NAME: zookeeper
+LAST DEPLOYED: Wed Apr 11 17:09:48 2018
+NAMESPACE: default
+STATUS: DEPLOYED
+
+RESOURCES:
+==> v1beta1/PodDisruptionBudget
+NAME MIN AVAILABLE MAX UNAVAILABLE ALLOWED DISRUPTIONS AGE
+zookeeper N/A 1 1 2m
+
+==> v1/Service
+NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
+zookeeper-headless ClusterIP None <none> 2181/TCP,3888/TCP,2888/TCP 2m
+zookeeper ClusterIP 10.98.179.165 <none> 2181/TCP 2m
+
+==> v1beta1/StatefulSet
+NAME DESIRED CURRENT AGE
+zookeeper 3 3 2m
+```
+
+1. `statefulsets/zookeeper` is the StatefulSet created by the chart.
+1. `po/zookeeper-<0|1|2>` are the Pods created by the StatefulSet. Each Pod has a single container running a ZooKeeper server.
+1. `svc/zookeeper-headless` is the Headless Service used to control the network domain of the ZooKeeper ensemble.
+1. `svc/zookeeper` is a Service that can be used by clients to connect to an available ZooKeeper server.
+
+## Configuration
+You can specify each parameter using the `--set key=value[,key=value]` argument to `helm install`.
+
+Alternatively, a YAML file that specifies the values for the parameters can be provided while installing the chart. For example,
+
+```console
+$ helm install --name my-release -f values.yaml incubator/zookeeper
+```
+
+## Default Values
+
+- You can find all user-configurable settings, their defaults and commentary about them in [values.yaml](values.yaml).
+
+## Deep Dive
+
+## Image Details
+The image used for this chart is based on Ubuntu 16.04 LTS. This image is larger than Alpine or BusyBox, but it provides glibc, rather than ulibc or mucl, and a JVM release that is built against it. You can easily convert this chart to run against a smaller image with a JVM that is built against that image's libc. However, as far as we know, no Hadoop vendor supports, or has verified, ZooKeeper running on such a JVM.
+
+## JVM Details
+The Java Virtual Machine used for this chart is the OpenJDK JVM 8u111 JRE (headless).
+
+## ZooKeeper Details
+The ZooKeeper version is the latest stable version (3.4.10). The distribution is installed into /opt/zookeeper-3.4.10. This directory is symbolically linked to /opt/zookeeper. Symlinks are created to simulate a rpm installation into /usr.
+
+## Failover
+You can test failover by killing the leader. Insert a key:
+```console
+$ kubectl exec zookeeper-0 -- /opt/zookeeper/bin/zkCli.sh create /foo bar;
+$ kubectl exec zookeeper-2 -- /opt/zookeeper/bin/zkCli.sh get /foo;
+```
+
+Watch existing members:
+```console
+$ kubectl run --attach bbox --image=busybox --restart=Never -- sh -c 'while true; do for i in 0 1 2; do echo zk-${i} $(echo stats | nc <pod-name>-${i}.<headless-service-name>:2181 | grep Mode); sleep 1; done; done';
+
+zk-2 Mode: follower
+zk-0 Mode: follower
+zk-1 Mode: leader
+zk-2 Mode: follower
+```
+
+Delete Pods and wait for the StatefulSet controller to bring them back up:
+```console
+$ kubectl delete po -l app=zookeeper
+$ kubectl get po --watch-only
+NAME READY STATUS RESTARTS AGE
+zookeeper-0 0/1 Running 0 35s
+zookeeper-0 1/1 Running 0 50s
+zookeeper-1 0/1 Pending 0 0s
+zookeeper-1 0/1 Pending 0 0s
+zookeeper-1 0/1 ContainerCreating 0 0s
+zookeeper-1 0/1 Running 0 19s
+zookeeper-1 1/1 Running 0 40s
+zookeeper-2 0/1 Pending 0 0s
+zookeeper-2 0/1 Pending 0 0s
+zookeeper-2 0/1 ContainerCreating 0 0s
+zookeeper-2 0/1 Running 0 19s
+zookeeper-2 1/1 Running 0 41s
+```
+
+Check the previously inserted key:
+```console
+$ kubectl exec zookeeper-1 -- /opt/zookeeper/bin/zkCli.sh get /foo
+ionid = 0x354887858e80035, negotiated timeout = 30000
+
+WATCHER::
+
+WatchedEvent state:SyncConnected type:None path:null
+bar
+```
+
+## Scaling
+ZooKeeper can not be safely scaled in versions prior to 3.5.x. This chart currently uses 3.4.x. There are manual procedures for scaling a 3.4.x ensemble, but as noted in the [ZooKeeper 3.5.2 documentation](https://zookeeper.apache.org/doc/r3.5.2-alpha/zookeeperReconfig.html) these procedures require a rolling restart, are known to be error prone, and often result in a data loss.
+
+While ZooKeeper 3.5.x does allow for dynamic ensemble reconfiguration (including scaling membership), the current status of the release is still alpha, and 3.5.x is therefore not recommended for production use.
+
+## Limitations
+* StatefulSet and PodDisruptionBudget are beta resources.
+* Only supports storage options that have backends for persistent volume claims.