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@@ -13,13 +13,12 @@ weight: 10
<!-- overview -->
This tutorial provides an introduction to managing applications with
[StatefulSets](/docs/concepts/workloads/controllers/statefulset/). It
[StatefulSets](/docs/concepts/workloads/controllers/statefulset/). It
demonstrates how to create, delete, scale, and update the Pods of StatefulSets.
## {{% heading "prerequisites" %}}
Before you begin this tutorial, you should familiarize yourself with the
Before you begin this tutorial, you should familiarize yourself with the
following Kubernetes concepts.
* [Pods](/docs/concepts/workloads/pods/)
@@ -30,18 +29,17 @@ following Kubernetes concepts.
* [StatefulSets](/docs/concepts/workloads/controllers/statefulset/)
* [kubectl CLI](/docs/user-guide/kubectl/)
This tutorial assumes that your cluster is configured to dynamically provision
This tutorial assumes that your cluster is configured to dynamically provision
PersistentVolumes. If your cluster is not configured to do so, you
will have to manually provision two 1 GiB volumes prior to starting this
will have to manually provision two 1 GiB volumes prior to starting this
tutorial.
## {{% heading "objectives" %}}
StatefulSets are intended to be used with stateful applications and distributed
systems. However, the administration of stateful applications and
distributed systems on Kubernetes is a broad, complex topic. In order to
demonstrate the basic features of a StatefulSet, and not to conflate the former
StatefulSets are intended to be used with stateful applications and distributed
systems. However, the administration of stateful applications and
distributed systems on Kubernetes is a broad, complex topic. In order to
demonstrate the basic features of a StatefulSet, and not to conflate the former
topic with the latter, you will deploy a simple web application using a StatefulSet.
After this tutorial, you will be familiar with the following.
@@ -52,29 +50,29 @@ After this tutorial, you will be familiar with the following.
* How to scale a StatefulSet
* How to update a StatefulSet's Pods
<!-- lessoncontent -->
## Creating a StatefulSet
Begin by creating a StatefulSet using the example below. It is similar to the
## Creating a StatefulSet
Begin by creating a StatefulSet using the example below. It is similar to the
example presented in the
[StatefulSets](/docs/concepts/workloads/controllers/statefulset/) concept.
It creates a [Headless Service](/docs/concepts/services-networking/service/#headless-services),
`nginx`, to publish the IP addresses of Pods in the StatefulSet, `web`.
[StatefulSets](/docs/concepts/workloads/controllers/statefulset/) concept.
It creates a [Headless Service](/docs/concepts/services-networking/service/#headless-services),
`nginx`, to publish the IP addresses of Pods in the StatefulSet, `web`.
{{< codenew file="application/web/web.yaml" >}}
Download the example above, and save it to a file named `web.yaml`
You will need to use two terminal windows. In the first terminal, use
[`kubectl get`](/docs/reference/generated/kubectl/kubectl-commands/#get) to watch the creation
You will need to use two terminal windows. In the first terminal, use
[`kubectl get`](/docs/reference/generated/kubectl/kubectl-commands/#get) to watch the creation
of the StatefulSet's Pods.
```shell
kubectl get pods -w -l app=nginx
```
In the second terminal, use
In the second terminal, use
[`kubectl apply`](/docs/reference/generated/kubectl/kubectl-commands/#apply) to create the
Headless Service and StatefulSet defined in `web.yaml`.
@@ -84,8 +82,8 @@ service/nginx created
statefulset.apps/web created
```
The command above creates two Pods, each running an
[NGINX](https://www.nginx.com) webserver. Get the `nginx` Service and the
The command above creates two Pods, each running an
[NGINX](https://www.nginx.com) webserver. Get the `nginx` Service and the
`web` StatefulSet to verify that they were created successfully.
```shell
@@ -100,9 +98,9 @@ web 2 1 20s
### Ordered Pod Creation
For a StatefulSet with N replicas, when Pods are being deployed, they are
created sequentially, in order from {0..N-1}. Examine the output of the
`kubectl get` command in the first terminal. Eventually, the output will
For a StatefulSet with N replicas, when Pods are being deployed, they are
created sequentially, in order from {0..N-1}. Examine the output of the
`kubectl get` command in the first terminal. Eventually, the output will
look like the example below.
```shell
@@ -118,8 +116,8 @@ web-1 0/1 ContainerCreating 0 0s
web-1 1/1 Running 0 18s
```
Notice that the `web-1` Pod is not launched until the `web-0` Pod is
[Running and Ready](/docs/user-guide/pod-states).
Notice that the `web-1` Pod is not launched until the `web-0` Pod is
[Running and Ready](/docs/user-guide/pod-states).
## Pods in a StatefulSet
@@ -137,18 +135,18 @@ web-1 1/1 Running 0 1m
```
As mentioned in the [StatefulSets](/docs/concepts/workloads/controllers/statefulset/)
concept, the Pods in a StatefulSet have a sticky, unique identity. This identity
is based on a unique ordinal index that is assigned to each Pod by the
StatefulSet controller. The Pods' names take the form
`<statefulset name>-<ordinal index>`. Since the `web` StatefulSet has two
As mentioned in the [StatefulSets](/docs/concepts/workloads/controllers/statefulset/)
concept, the Pods in a StatefulSet have a sticky, unique identity. This identity
is based on a unique ordinal index that is assigned to each Pod by the
StatefulSet controller. The Pods' names take the form
`<statefulset name>-<ordinal index>`. Since the `web` StatefulSet has two
replicas, it creates two Pods, `web-0` and `web-1`.
### Using Stable Network Identities
Each Pod has a stable hostname based on its ordinal index. Use
[`kubectl exec`](/docs/reference/generated/kubectl/kubectl-commands/#exec) to execute the
`hostname` command in each Pod.
[`kubectl exec`](/docs/reference/generated/kubectl/kubectl-commands/#exec) to execute the
`hostname` command in each Pod.
```shell
for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done
@@ -156,9 +154,9 @@ web-0
web-1
```
Use [`kubectl run`](/docs/reference/generated/kubectl/kubectl-commands/#run) to execute
a container that provides the `nslookup` command from the `dnsutils` package.
Using `nslookup` on the Pods' hostnames, you can examine their in-cluster DNS
Use [`kubectl run`](/docs/reference/generated/kubectl/kubectl-commands/#run) to execute
a container that provides the `nslookup` command from the `dnsutils` package.
Using `nslookup` on the Pods' hostnames, you can examine their in-cluster DNS
addresses.
```shell
@@ -178,17 +176,17 @@ Name: web-1.nginx
Address 1: 10.244.2.6
```
The CNAME of the headless service points to SRV records (one for each Pod that
is Running and Ready). The SRV records point to A record entries that
contain the Pods' IP addresses.
The CNAME of the headless service points to SRV records (one for each Pod that
is Running and Ready). The SRV records point to A record entries that
contain the Pods' IP addresses.
In one terminal, watch the StatefulSet's Pods.
In one terminal, watch the StatefulSet's Pods.
```shell
kubectl get pod -w -l app=nginx
```
In a second terminal, use
[`kubectl delete`](/docs/reference/generated/kubectl/kubectl-commands/#delete) to delete all
[`kubectl delete`](/docs/reference/generated/kubectl/kubectl-commands/#delete) to delete all
the Pods in the StatefulSet.
```shell
@@ -197,7 +195,7 @@ pod "web-0" deleted
pod "web-1" deleted
```
Wait for the StatefulSet to restart them, and for both Pods to transition to
Wait for the StatefulSet to restart them, and for both Pods to transition to
Running and Ready.
```shell
@@ -212,7 +210,7 @@ web-1 0/1 ContainerCreating 0 0s
web-1 1/1 Running 0 34s
```
Use `kubectl exec` and `kubectl run` to view the Pods hostnames and in-cluster
Use `kubectl exec` and `kubectl run` to view the Pods hostnames and in-cluster
DNS entries.
```shell
@@ -220,7 +218,7 @@ for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done
web-0
web-1
kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm /bin/sh
kubectl run -i --tty --image busybox:1.28 dns-test --restart=Never --rm /bin/sh
nslookup web-0.nginx
Server: 10.0.0.10
Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local
@@ -236,23 +234,23 @@ Name: web-1.nginx
Address 1: 10.244.2.8
```
The Pods' ordinals, hostnames, SRV records, and A record names have not changed,
but the IP addresses associated with the Pods may have changed. In the cluster
used for this tutorial, they have. This is why it is important not to configure
The Pods' ordinals, hostnames, SRV records, and A record names have not changed,
but the IP addresses associated with the Pods may have changed. In the cluster
used for this tutorial, they have. This is why it is important not to configure
other applications to connect to Pods in a StatefulSet by IP address.
If you need to find and connect to the active members of a StatefulSet, you
should query the CNAME of the Headless Service
(`nginx.default.svc.cluster.local`). The SRV records associated with the
CNAME will contain only the Pods in the StatefulSet that are Running and
If you need to find and connect to the active members of a StatefulSet, you
should query the CNAME of the Headless Service
(`nginx.default.svc.cluster.local`). The SRV records associated with the
CNAME will contain only the Pods in the StatefulSet that are Running and
Ready.
If your application already implements connection logic that tests for
liveness and readiness, you can use the SRV records of the Pods (
If your application already implements connection logic that tests for
liveness and readiness, you can use the SRV records of the Pods (
`web-0.nginx.default.svc.cluster.local`,
`web-1.nginx.default.svc.cluster.local`), as they are stable, and your
application will be able to discover the Pods' addresses when they transition
`web-1.nginx.default.svc.cluster.local`), as they are stable, and your
application will be able to discover the Pods' addresses when they transition
to Running and Ready.
### Writing to Stable Storage
@@ -265,16 +263,16 @@ NAME STATUS VOLUME CAPACITY ACCE
www-web-0 Bound pvc-15c268c7-b507-11e6-932f-42010a800002 1Gi RWO 48s
www-web-1 Bound pvc-15c79307-b507-11e6-932f-42010a800002 1Gi RWO 48s
```
The StatefulSet controller created two PersistentVolumeClaims that are
bound to two [PersistentVolumes](/docs/concepts/storage/persistent-volumes/). As the cluster used in this tutorial is configured to dynamically provision
The StatefulSet controller created two PersistentVolumeClaims that are
bound to two [PersistentVolumes](/docs/concepts/storage/persistent-volumes/). As the cluster used in this tutorial is configured to dynamically provision
PersistentVolumes, the PersistentVolumes were created and bound automatically.
The NGINX webservers, by default, will serve an index file at
`/usr/share/nginx/html/index.html`. The `volumeMounts` field in the
StatefulSets `spec` ensures that the `/usr/share/nginx/html` directory is
The NGINX webservers, by default, will serve an index file at
`/usr/share/nginx/html/index.html`. The `volumeMounts` field in the
StatefulSets `spec` ensures that the `/usr/share/nginx/html` directory is
backed by a PersistentVolume.
Write the Pods' hostnames to their `index.html` files and verify that the NGINX
Write the Pods' hostnames to their `index.html` files and verify that the NGINX
webservers serve the hostnames.
```shell
@@ -310,7 +308,7 @@ kubectl delete pod -l app=nginx
pod "web-0" deleted
pod "web-1" deleted
```
Examine the output of the `kubectl get` command in the first terminal, and wait
Examine the output of the `kubectl get` command in the first terminal, and wait
for all of the Pods to transition to Running and Ready.
```shell
@@ -333,14 +331,14 @@ web-0
web-1
```
Even though `web-0` and `web-1` were rescheduled, they continue to serve their
hostnames because the PersistentVolumes associated with their
PersistentVolumeClaims are remounted to their `volumeMounts`. No matter what
node `web-0`and `web-1` are scheduled on, their PersistentVolumes will be
Even though `web-0` and `web-1` were rescheduled, they continue to serve their
hostnames because the PersistentVolumes associated with their
PersistentVolumeClaims are remounted to their `volumeMounts`. No matter what
node `web-0`and `web-1` are scheduled on, their PersistentVolumes will be
mounted to the appropriate mount points.
## Scaling a StatefulSet
Scaling a StatefulSet refers to increasing or decreasing the number of replicas.
Scaling a StatefulSet refers to increasing or decreasing the number of replicas.
This is accomplished by updating the `replicas` field. You can use either
[`kubectl scale`](/docs/reference/generated/kubectl/kubectl-commands/#scale) or
[`kubectl patch`](/docs/reference/generated/kubectl/kubectl-commands/#patch) to scale a StatefulSet.
@@ -353,7 +351,7 @@ In one terminal window, watch the Pods in the StatefulSet.
kubectl get pods -w -l app=nginx
```
In another terminal window, use `kubectl scale` to scale the number of replicas
In another terminal window, use `kubectl scale` to scale the number of replicas
to 5.
```shell
@@ -361,7 +359,7 @@ kubectl scale sts web --replicas=5
statefulset.apps/web scaled
```
Examine the output of the `kubectl get` command in the first terminal, and wait
Examine the output of the `kubectl get` command in the first terminal, and wait
for the three additional Pods to transition to Running and Ready.
```shell
@@ -386,8 +384,8 @@ web-4 1/1 Running 0 19s
The StatefulSet controller scaled the number of replicas. As with
[StatefulSet creation](#ordered-pod-creation), the StatefulSet controller
created each Pod sequentially with respect to its ordinal index, and it
waited for each Pod's predecessor to be Running and Ready before launching the
created each Pod sequentially with respect to its ordinal index, and it
waited for each Pod's predecessor to be Running and Ready before launching the
subsequent Pod.
### Scaling Down
@@ -398,7 +396,7 @@ In one terminal, watch the StatefulSet's Pods.
kubectl get pods -w -l app=nginx
```
In another terminal, use `kubectl patch` to scale the StatefulSet back down to
In another terminal, use `kubectl patch` to scale the StatefulSet back down to
three replicas.
```shell
@@ -426,11 +424,11 @@ web-3 1/1 Terminating 0 42s
### Ordered Pod Termination
The controller deleted one Pod at a time, in reverse order with respect to its
ordinal index, and it waited for each to be completely shutdown before
The controller deleted one Pod at a time, in reverse order with respect to its
ordinal index, and it waited for each to be completely shutdown before
deleting the next.
Get the StatefulSet's PersistentVolumeClaims.
Get the StatefulSet's PersistentVolumeClaims.
```shell
kubectl get pvc -l app=nginx
@@ -443,23 +441,23 @@ www-web-4 Bound pvc-e11bb5f8-b508-11e6-932f-42010a800002 1Gi RWO
```
There are still five PersistentVolumeClaims and five PersistentVolumes.
When exploring a Pod's [stable storage](#writing-to-stable-storage), we saw that the PersistentVolumes mounted to the Pods of a StatefulSet are not deleted when the StatefulSet's Pods are deleted. This is still true when Pod deletion is caused by scaling the StatefulSet down.
There are still five PersistentVolumeClaims and five PersistentVolumes.
When exploring a Pod's [stable storage](#writing-to-stable-storage), we saw that the PersistentVolumes mounted to the Pods of a StatefulSet are not deleted when the StatefulSet's Pods are deleted. This is still true when Pod deletion is caused by scaling the StatefulSet down.
## Updating StatefulSets
In Kubernetes 1.7 and later, the StatefulSet controller supports automated updates. The
strategy used is determined by the `spec.updateStrategy` field of the
StatefulSet API Object. This feature can be used to upgrade the container
images, resource requests and/or limits, labels, and annotations of the Pods in a
StatefulSet. There are two valid update strategies, `RollingUpdate` and
In Kubernetes 1.7 and later, the StatefulSet controller supports automated updates. The
strategy used is determined by the `spec.updateStrategy` field of the
StatefulSet API Object. This feature can be used to upgrade the container
images, resource requests and/or limits, labels, and annotations of the Pods in a
StatefulSet. There are two valid update strategies, `RollingUpdate` and
`OnDelete`.
`RollingUpdate` update strategy is the default for StatefulSets.
### Rolling Update
The `RollingUpdate` update strategy will update all Pods in a StatefulSet, in
The `RollingUpdate` update strategy will update all Pods in a StatefulSet, in
reverse ordinal order, while respecting the StatefulSet guarantees.
Patch the `web` StatefulSet to apply the `RollingUpdate` update strategy.
@@ -469,7 +467,7 @@ kubectl patch statefulset web -p '{"spec":{"updateStrategy":{"type":"RollingUpda
statefulset.apps/web patched
```
In one terminal window, patch the `web` StatefulSet to change the container
In one terminal window, patch the `web` StatefulSet to change the container
image again.
```shell
@@ -515,15 +513,15 @@ web-0 0/1 ContainerCreating 0 0s
web-0 1/1 Running 0 10s
```
The Pods in the StatefulSet are updated in reverse ordinal order. The
StatefulSet controller terminates each Pod, and waits for it to transition to Running and
Ready prior to updating the next Pod. Note that, even though the StatefulSet
controller will not proceed to update the next Pod until its ordinal successor
is Running and Ready, it will restore any Pod that fails during the update to
its current version. Pods that have already received the update will be
restored to the updated version, and Pods that have not yet received the
update will be restored to the previous version. In this way, the controller
attempts to continue to keep the application healthy and the update consistent
The Pods in the StatefulSet are updated in reverse ordinal order. The
StatefulSet controller terminates each Pod, and waits for it to transition to Running and
Ready prior to updating the next Pod. Note that, even though the StatefulSet
controller will not proceed to update the next Pod until its ordinal successor
is Running and Ready, it will restore any Pod that fails during the update to
its current version. Pods that have already received the update will be
restored to the updated version, and Pods that have not yet received the
update will be restored to the previous version. In this way, the controller
attempts to continue to keep the application healthy and the update consistent
in the presence of intermittent failures.
Get the Pods to view their container images.
@@ -538,13 +536,13 @@ k8s.gcr.io/nginx-slim:0.8
All the Pods in the StatefulSet are now running the previous container image.
**Tip** You can also use `kubectl rollout status sts/<name>` to view
**Tip** You can also use `kubectl rollout status sts/<name>` to view
the status of a rolling update.
#### Staging an Update
You can stage an update to a StatefulSet by using the `partition` parameter of
the `RollingUpdate` update strategy. A staged update will keep all of the Pods
in the StatefulSet at the current version while allowing mutations to the
You can stage an update to a StatefulSet by using the `partition` parameter of
the `RollingUpdate` update strategy. A staged update will keep all of the Pods
in the StatefulSet at the current version while allowing mutations to the
StatefulSet's `.spec.template`.
Patch the `web` StatefulSet to add a partition to the `updateStrategy` field.
@@ -587,13 +585,13 @@ k8s.gcr.io/nginx-slim:0.8
```
Notice that, even though the update strategy is `RollingUpdate` the StatefulSet
controller restored the Pod with its original container. This is because the
ordinal of the Pod is less than the `partition` specified by the
Notice that, even though the update strategy is `RollingUpdate` the StatefulSet
controller restored the Pod with its original container. This is because the
ordinal of the Pod is less than the `partition` specified by the
`updateStrategy`.
#### Rolling Out a Canary
You can roll out a canary to test a modification by decrementing the `partition`
You can roll out a canary to test a modification by decrementing the `partition`
you specified [above](#staging-an-update).
Patch the StatefulSet to decrement the partition.
@@ -622,8 +620,8 @@ k8s.gcr.io/nginx-slim:0.7
```
When you changed the `partition`, the StatefulSet controller automatically
updated the `web-2` Pod because the Pod's ordinal was greater than or equal to
When you changed the `partition`, the StatefulSet controller automatically
updated the `web-2` Pod because the Pod's ordinal was greater than or equal to
the `partition`.
Delete the `web-1` Pod.
@@ -657,19 +655,19 @@ kubectl get po web-1 --template '{{range $i, $c := .spec.containers}}{{$c.image}
k8s.gcr.io/nginx-slim:0.8
```
`web-1` was restored to its original configuration because the Pod's ordinal
was less than the partition. When a partition is specified, all Pods with an
ordinal that is greater than or equal to the partition will be updated when the
StatefulSet's `.spec.template` is updated. If a Pod that has an ordinal less
than the partition is deleted or otherwise terminated, it will be restored to
`web-1` was restored to its original configuration because the Pod's ordinal
was less than the partition. When a partition is specified, all Pods with an
ordinal that is greater than or equal to the partition will be updated when the
StatefulSet's `.spec.template` is updated. If a Pod that has an ordinal less
than the partition is deleted or otherwise terminated, it will be restored to
its original configuration.
#### Phased Roll Outs
You can perform a phased roll out (e.g. a linear, geometric, or exponential
roll out) using a partitioned rolling update in a similar manner to how you
rolled out a [canary](#rolling-out-a-canary). To perform a phased roll out, set
the `partition` to the ordinal at which you want the controller to pause the
update.
roll out) using a partitioned rolling update in a similar manner to how you
rolled out a [canary](#rolling-out-a-canary). To perform a phased roll out, set
the `partition` to the ordinal at which you want the controller to pause the
update.
The partition is currently set to `2`. Set the partition to `0`.
@@ -709,22 +707,22 @@ k8s.gcr.io/nginx-slim:0.7
```
By moving the `partition` to `0`, you allowed the StatefulSet controller to
By moving the `partition` to `0`, you allowed the StatefulSet controller to
continue the update process.
### On Delete
The `OnDelete` update strategy implements the legacy (1.6 and prior) behavior,
When you select this update strategy, the StatefulSet controller will not
automatically update Pods when a modification is made to the StatefulSet's
`.spec.template` field. This strategy can be selected by setting the
The `OnDelete` update strategy implements the legacy (1.6 and prior) behavior,
When you select this update strategy, the StatefulSet controller will not
automatically update Pods when a modification is made to the StatefulSet's
`.spec.template` field. This strategy can be selected by setting the
`.spec.template.updateStrategy.type` to `OnDelete`.
## Deleting StatefulSets
StatefulSet supports both Non-Cascading and Cascading deletion. In a
Non-Cascading Delete, the StatefulSet's Pods are not deleted when the StatefulSet is deleted. In a Cascading Delete, both the StatefulSet and its Pods are
StatefulSet supports both Non-Cascading and Cascading deletion. In a
Non-Cascading Delete, the StatefulSet's Pods are not deleted when the StatefulSet is deleted. In a Cascading Delete, both the StatefulSet and its Pods are
deleted.
### Non-Cascading Delete
@@ -735,9 +733,9 @@ In one terminal window, watch the Pods in the StatefulSet.
kubectl get pods -w -l app=nginx
```
Use [`kubectl delete`](/docs/reference/generated/kubectl/kubectl-commands/#delete) to delete the
StatefulSet. Make sure to supply the `--cascade=false` parameter to the
command. This parameter tells Kubernetes to only delete the StatefulSet, and to
Use [`kubectl delete`](/docs/reference/generated/kubectl/kubectl-commands/#delete) to delete the
StatefulSet. Make sure to supply the `--cascade=false` parameter to the
command. This parameter tells Kubernetes to only delete the StatefulSet, and to
not delete any of its Pods.
```shell
@@ -781,7 +779,7 @@ kubectl get pods -w -l app=nginx
```
In a second terminal, recreate the StatefulSet. Note that, unless
you deleted the `nginx` Service ( which you should not have ), you will see
you deleted the `nginx` Service ( which you should not have ), you will see
an error indicating that the Service already exists.
```shell
@@ -791,7 +789,7 @@ service/nginx unchanged
```
Ignore the error. It only indicates that an attempt was made to create the nginx
Headless Service even though that Service already exists.
Headless Service even though that Service already exists.
Examine the output of the `kubectl get` command running in the first terminal.
@@ -811,14 +809,14 @@ web-2 0/1 Terminating 0 3m
web-2 0/1 Terminating 0 3m
```
When the `web` StatefulSet was recreated, it first relaunched `web-0`.
When the `web` StatefulSet was recreated, it first relaunched `web-0`.
Since `web-1` was already Running and Ready, when `web-0` transitioned to
Running and Ready, it simply adopted this Pod. Since you recreated the StatefulSet
with `replicas` equal to 2, once `web-0` had been recreated, and once
`web-1` had been determined to already be Running and Ready, `web-2` was
terminated.
Running and Ready, it simply adopted this Pod. Since you recreated the StatefulSet
with `replicas` equal to 2, once `web-0` had been recreated, and once
`web-1` had been determined to already be Running and Ready, `web-2` was
terminated.
Let's take another look at the contents of the `index.html` file served by the
Let's take another look at the contents of the `index.html` file served by the
Pods' webservers.
```shell
@@ -827,10 +825,10 @@ web-0
web-1
```
Even though you deleted both the StatefulSet and the `web-0` Pod, it still
serves the hostname originally entered into its `index.html` file. This is
because the StatefulSet never deletes the PersistentVolumes associated with a
Pod. When you recreated the StatefulSet and it relaunched `web-0`, its original
Even though you deleted both the StatefulSet and the `web-0` Pod, it still
serves the hostname originally entered into its `index.html` file. This is
because the StatefulSet never deletes the PersistentVolumes associated with a
Pod. When you recreated the StatefulSet and it relaunched `web-0`, its original
PersistentVolume was remounted.
### Cascading Delete
@@ -841,14 +839,14 @@ In one terminal window, watch the Pods in the StatefulSet.
kubectl get pods -w -l app=nginx
```
In another terminal, delete the StatefulSet again. This time, omit the
In another terminal, delete the StatefulSet again. This time, omit the
`--cascade=false` parameter.
```shell
kubectl delete statefulset web
statefulset.apps "web" deleted
```
Examine the output of the `kubectl get` command running in the first terminal,
Examine the output of the `kubectl get` command running in the first terminal,
and wait for all of the Pods to transition to Terminating.
```shell
@@ -868,12 +866,12 @@ web-1 0/1 Terminating 0 29m
```
As you saw in the [Scaling Down](#scaling-down) section, the Pods
are terminated one at a time, with respect to the reverse order of their ordinal
indices. Before terminating a Pod, the StatefulSet controller waits for
As you saw in the [Scaling Down](#scaling-down) section, the Pods
are terminated one at a time, with respect to the reverse order of their ordinal
indices. Before terminating a Pod, the StatefulSet controller waits for
the Pod's successor to be completely terminated.
Note that, while a cascading delete will delete the StatefulSet and its Pods,
Note that, while a cascading delete will delete the StatefulSet and its Pods,
it will not delete the Headless Service associated with the StatefulSet. You
must delete the `nginx` Service manually.
@@ -890,7 +888,7 @@ service/nginx created
statefulset.apps/web created
```
When all of the StatefulSet's Pods transition to Running and Ready, retrieve
When all of the StatefulSet's Pods transition to Running and Ready, retrieve
the contents of their `index.html` files.
```shell
@@ -899,8 +897,8 @@ web-0
web-1
```
Even though you completely deleted the StatefulSet, and all of its Pods, the
Pods are recreated with their PersistentVolumes mounted, and `web-0` and
Even though you completely deleted the StatefulSet, and all of its Pods, the
Pods are recreated with their PersistentVolumes mounted, and `web-0` and
`web-1` will still serve their hostnames.
Finally delete the `web` StatefulSet and the `nginx` service.
@@ -915,29 +913,29 @@ statefulset "web" deleted
## Pod Management Policy
For some distributed systems, the StatefulSet ordering guarantees are
unnecessary and/or undesirable. These systems require only uniqueness and
identity. To address this, in Kubernetes 1.7, we introduced
`.spec.podManagementPolicy` to the StatefulSet API Object.
For some distributed systems, the StatefulSet ordering guarantees are
unnecessary and/or undesirable. These systems require only uniqueness and
identity. To address this, in Kubernetes 1.7, we introduced
`.spec.podManagementPolicy` to the StatefulSet API Object.
### OrderedReady Pod Management
`OrderedReady` pod management is the default for StatefulSets. It tells the
StatefulSet controller to respect the ordering guarantees demonstrated
`OrderedReady` pod management is the default for StatefulSets. It tells the
StatefulSet controller to respect the ordering guarantees demonstrated
above.
### Parallel Pod Management
`Parallel` pod management tells the StatefulSet controller to launch or
terminate all Pods in parallel, and not to wait for Pods to become Running
and Ready or completely terminated prior to launching or terminating another
`Parallel` pod management tells the StatefulSet controller to launch or
terminate all Pods in parallel, and not to wait for Pods to become Running
and Ready or completely terminated prior to launching or terminating another
Pod.
{{< codenew file="application/web/web-parallel.yaml" >}}
Download the example above, and save it to a file named `web-parallel.yaml`
This manifest is identical to the one you downloaded above except that the `.spec.podManagementPolicy`
This manifest is identical to the one you downloaded above except that the `.spec.podManagementPolicy`
of the `web` StatefulSet is set to `Parallel`.
In one terminal, watch the Pods in the StatefulSet.
@@ -971,7 +969,7 @@ web-1 1/1 Running 0 10s
The StatefulSet controller launched both `web-0` and `web-1` at the same time.
Keep the second terminal open, and, in another terminal window scale the
Keep the second terminal open, and, in another terminal window scale the
StatefulSet.
```shell
@@ -991,7 +989,7 @@ web-3 1/1 Running 0 26s
```
The StatefulSet controller launched two new Pods, and it did not wait for
The StatefulSet controller launched two new Pods, and it did not wait for
the first to become Running and Ready prior to launching the second.
Keep this terminal open, and in another terminal delete the `web` StatefulSet.
@@ -1028,10 +1026,10 @@ web-3 0/1 Terminating 0 9m
web-3 0/1 Terminating 0 9m
```
The StatefulSet controller deletes all Pods concurrently, it does not wait for
The StatefulSet controller deletes all Pods concurrently, it does not wait for
a Pod's ordinal successor to terminate prior to deleting that Pod.
Close the terminal where the `kubectl get` command is running and delete the `nginx`
Close the terminal where the `kubectl get` command is running and delete the `nginx`
Service.
```shell
@@ -1042,9 +1040,6 @@ kubectl delete svc nginx
## {{% heading "cleanup" %}}
You will need to delete the persistent storage media for the PersistentVolumes
used in this tutorial. Follow the necessary steps, based on your environment,
storage configuration, and provisioning method, to ensure that all storage is
used in this tutorial. Follow the necessary steps, based on your environment,
storage configuration, and provisioning method, to ensure that all storage is
reclaimed.