Kenneth Owens
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---
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{% capture overview %}
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This tutorial provides an introduction to the
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[StatefulSet](/docs/concepts/controllers/statefulsets/) concept. It
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This tutorial provides an introduction to managing applications with
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[StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/). It
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demonstrates how to create, delete, scale, and update the container image of a
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StatefulSet.
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{% endcapture %}
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@ -25,7 +25,7 @@ following Kubernetes concepts.
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* [Headless Services](/docs/user-guide/services/#headless-services)
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* [PersistentVolumes](/docs/user-guide/volumes/)
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* [PersistentVolume Provisioning](http://releases.k8s.io/{{page.githubbranch}}/examples/experimental/persistent-volume-provisioning/)
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* [StatefulSets](/docs/concepts/controllers/statefulsets/)
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* [StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/)
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* [kubectl CLI](/docs/user-guide/kubectl)
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This tutorial assumes that your cluster is configured to dynamically provision
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@ -55,7 +55,7 @@ After this tutorial, you will be familiar with the following.
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Begin by creating a StatefulSet using the example below. It is similar to the
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example presented in the
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[StatefulSets](/docs/concepts/controllers/statefulsets/) concept. It creates
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[StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/) concept. It creates
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a [Headless Service](/docs/user-guide/services/#headless-services), `nginx`, to
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control the domain of the StatefulSet, `web`.
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@ -121,8 +121,10 @@ launching `web-1`. In fact, `web-1` is not launched until `web-0` is
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[Running and Ready](/docs/user-guide/pod-states).
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### Pods in a StatefulSet
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Unlike Pods in other controllers, the Pods in a StatefulSet have a unqiue
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ordinal index and a stable network identity.
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#### Ordinal Index
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#### Examining the Pod's Ordinal Index
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Get the StatefulSet's Pods.
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@ -134,14 +136,14 @@ web-1 1/1 Running 0 1m
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```
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As mentioned in the [StatefulSets](/docs/concepts/controllers/statefulsets/)
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As mentioned in the [StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/)
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concept, the Pods in a StatefulSet have a sticky, unique identity. This identity
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is based on a unique ordinal index that is assigned to each Pod by the Stateful
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Set controller. The Pods' names take the form
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`<statefulset name>-<ordinal index>`. Since the `web` StatefulSet has two
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replicas, it creates two Pods, `web-0` and `web-1`.
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#### Stable Network Identity
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#### Using Stable Network Identities
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Each Pod has a stable hostname based on its ordinal index. Use
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[`kubectl exec`](/docs/user-guide/kubectl/kubectl_exec/) to execute the
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`hostname` command in each Pod.
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@ -249,7 +251,7 @@ liveness and readiness, you should use the SRV records of the Pods in the
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StatefulSet (e.g `web-0.nginx.default.svc.cluster.local`,
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`web-1.nginx.default.svc.cluster.local`).
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#### Stable Storage
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#### Writing to Stable Storage
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Get the PersistentVolumeClaims for `web-0` and `web-1`.
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@ -323,9 +325,8 @@ and `web-1` are scheduled on, their PersistentVolumes will be mounted to the
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appropriate mount points.
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### Scaling a StatefulSet
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When we refer to scaling a StatefulSet, we mean increasing or decreasing the
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number of replicas in the StatefulSet. This is accomplished by updating
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the `replicas` field. You can use either
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Scaling a StatefulSet refers to increasing or decreasing the number of replicas.
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This is accomplished by updating the `replicas` field. You can use either
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[`kubectl scale`](/docs/user-guide/kubectl/kubectl_scale/) or
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[`kubectl patch`](/docs/user-guide/kubectl/kubectl_patch/) to scale a Stateful
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Set.
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@ -617,8 +618,8 @@ web-2 0/1 Terminating 0 3m
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When the `web` StatefulSet was recreated, it first relaunched `web-0`.
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Since `web-1` was already Running and Ready, when `web-0` transitioned to
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Running and Ready, it simply adopted this Pod. Since we recreated the Stateful
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Set with `replicas` equal to 2, once `web-0` had been recreated, and once
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Running and Ready, it simply adopted this Pod. Since you recreated the StatefulSet
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with `replicas` equal to 2, once `web-0` had been recreated, and once
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`web-1` had been determined to already be Running and Ready, `web-2` was
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terminated.
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@ -631,7 +632,7 @@ web-0
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web-1
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```
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Even though we deleted both the StatefulSet and the `web-0` Pod, it still
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Even though you deleted both the StatefulSet and the `web-0` Pod, it still
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serves the hostname originally entered into its `index.html` file. This is
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because the StatefulSet never deletes the PersistentVolumes associated with a
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Pod. When you recreated the StatefulSet and it relaunched `web-0`, its original
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@ -672,7 +673,7 @@ web-1 0/1 Terminating 0 29m
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```
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As we saw in the [Scaling Down](#ordered-pod-termination) section, the Pods
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As you saw in the [Scaling Down](#ordered-pod-termination) section, the Pods
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are terminated one at a time, with respect to the reverse order of their ordinal
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indices. Before terminating a Pod, the StatefulSet controller waits for
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the Pod's successor to be completely terminated.
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