diff --git a/_data/tutorials.yml b/_data/tutorials.yml index 1af2276a11..701fafac21 100644 --- a/_data/tutorials.yml +++ b/_data/tutorials.yml @@ -53,6 +53,8 @@ toc: path: /docs/tutorials/stateless-application/expose-external-ip-address/ - title: Stateful Applications section: + - title: StatefulSet Basics + path: /docs/tutorials/stateful-application/basic-stateful-set/ - title: Running a Single-Instance Stateful Application path: /docs/tutorials/stateful-application/run-stateful-application/ - title: Running a Replicated Stateful Application diff --git a/docs/tutorials/index.md b/docs/tutorials/index.md index bcec6590cf..eb20f13ee8 100644 --- a/docs/tutorials/index.md +++ b/docs/tutorials/index.md @@ -20,6 +20,8 @@ each of which has a sequence of steps. #### Stateful Applications +* [StatefulSet Basics](/docs/tutorials/stateful-application/basic-stateful-set/) + * [Running a Single-Instance Stateful Application](/docs/tutorials/stateful-application/run-stateful-application/) * [Running a Replicated Stateful Application](/docs/tutorials/stateful-application/run-replicated-stateful-application/) diff --git a/docs/tutorials/stateful-application/basic-stateful-set.md b/docs/tutorials/stateful-application/basic-stateful-set.md new file mode 100644 index 0000000000..952f4d20f0 --- /dev/null +++ b/docs/tutorials/stateful-application/basic-stateful-set.md @@ -0,0 +1,735 @@ +--- +assignees: +- bprashanth +- enisoc +- erictune +- foxish +- janetkuo +- kow3ns +- smarterclayton +--- + +{% capture overview %} +This tutorial provides an introduction to managing applications with +[StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/). It +demonstrates how to create, delete, scale, and update the container image of a +StatefulSet. +{% endcapture %} + +{% capture prerequisites %} +Before you begin this tutorial, you should familiarize yourself with the +following Kubernetes concepts. + +* [Pods](/docs/user-guide/pods/single-container/) +* [Cluster DNS](/docs/admin/dns/) +* [Headless Services](/docs/user-guide/services/#headless-services) +* [PersistentVolumes](/docs/user-guide/volumes/) +* [PersistentVolume Provisioning](http://releases.k8s.io/{{page.githubbranch}}/examples/experimental/persistent-volume-provisioning/) +* [StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/) +* [kubectl CLI](/docs/user-guide/kubectl) + +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 five 1 GiB volumes prior to starting this +tutorial. +{% endcapture %} + +{% capture 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 to not conflate the former +topic with the latter, you will deploy a simple web application using StatefulSets. + +After this tutorial, you will be familiar with the following. + +* How to create a StatefulSet +* How a StatefulSet manages its Pods +* How to delete a StatefulSet +* How to scale a StatefulSet +* How to update the container image of a StatefulSet's Pods +{% endcapture %} + +{% capture lessoncontent %} +### Creating a StatefulSet + +Begin by creating a StatefulSet using the example below. It is similar to the +example presented in the +[StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/) concept. It creates +a [Headless Service](/docs/user-guide/services/#headless-services), `nginx`, to +control the domain of the StatefulSet, `web`. + +{% include code.html language="yaml" file="web.yaml" ghlink="/docs/tutorials/stateful-application/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/user-guide/kubectl/kubectl_get/) to watch the creation +of the StatefulSet's Pods. + +```shell +kubectl get pods -w -l app=nginx +``` + +In the second terminal, use +[`kubectl create`](/docs/user-guide/kubectl/kubectl_create/) to create the +Headless Service and StatefulSet defined in `web.yaml`. + +```shell +kubectl create -f web.yml +service "nginx" created +statefulset "web" created +``` + +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 +kubectl get service nginx +NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE +nginx None 80/TCP 12s + +kubectl get statefulset web +NAME DESIRED CURRENT AGE +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 +look like the example below. + +```shell +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +NAME READY STATUS RESTARTS AGE +web-0 0/1 Pending 0 0s +web-0 0/1 Pending 0 0s +web-0 0/1 ContainerCreating 0 0s +web-0 1/1 Running 0 19s +web-1 0/1 Pending 0 0s +web-1 0/1 Pending 0 0s +web-1 0/1 ContainerCreating 0 0s +web-1 1/1 Running 0 18s +``` + +Notice that the `web-0` Pod is launched and set to Pending prior to +launching `web-1`. In fact, `web-1` is not launched until `web-0` is +[Running and Ready](/docs/user-guide/pod-states). + +### Pods in a StatefulSet +Unlike Pods in other controllers, the Pods in a StatefulSet have a unqiue +ordinal index and a stable network identity. + +#### Examining the Pod's Ordinal Index + +Get the StatefulSet's Pods. + +```shell +kubectl get pods -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 1m +web-1 1/1 Running 0 1m + +``` + +As mentioned in the [StatefulSets](/docs/concepts/abstractions/controllers/statefulsets/) +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 Stateful +Set controller. The Pods' names take the form +`-`. 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/user-guide/kubectl/kubectl_exec/) to execute the +`hostname` command in each Pod. + +```shell +for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done +web-0 +web-1 +``` + +Use [`kubectl run`](/docs/user-guide/kubectl/kubectl_run/) to execute +a container that provides the `nslookup` command from the `dnsutils` package. +Using `nslookup` on the Pods' hostnames, you can examine their in-cluster DNS +addresses. + +```shell +kubectl run -i --tty --image busybox dns-test --restart=Never --rm /bin/sh +nslookup web-0.nginx +Server: 10.0.0.10 +Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local + +Name: web-0.nginx +Address 1: 10.244.1.6 + +nslookup web-1.nginx +Server: 10.0.0.10 +Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local + +Name: web-1.nginx +Address 1: 10.244.2.6 +``` + +The CNAME of the headless serivce points to SRV records (one for each Pod that +is Running and Ready). The SRV records point to A record entries that +contain the Pods' IP addresses. + +In one terminal, watch the StatefulSet's Pods. + +```shell +kubectl get pod -w -l app=nginx +``` +In a second terminal, use +[`kubectl delete`](/docs/user-guide/kubectl/kubectl_delete/) to delete all +the Pods in the StatefulSet. + +```shell +kubectl delete pod -l app=nginx +pod "web-0" deleted +pod "web-1" deleted +``` + +Wait for the StatefulSet to restart them, and for both Pods to transition to +Running and Ready. + +```shell +kubectl get pod -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 0/1 ContainerCreating 0 0s +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 2s +web-1 0/1 Pending 0 0s +web-1 0/1 Pending 0 0s +web-1 0/1 ContainerCreating 0 0s +web-1 1/1 Running 0 34s +``` + +Use `kubectl exec` and `kubectl run` to view the Pods hostnames and in-cluster +DNS entries. + +```shell +for i in 0 1; do kubectl exec web-$i -- sh -c 'hostname'; done +web-0 +web-1 + +kubectl run -i --tty --image busybox 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 + +Name: web-0.nginx +Address 1: 10.244.1.7 + +nslookup web-1.nginx +Server: 10.0.0.10 +Address 1: 10.0.0.10 kube-dns.kube-system.svc.cluster.local + +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 +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 +Ready. + +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 +to Running and Ready. + +#### Writing to Stable Storage + +Get the PersistentVolumeClaims for `web-0` and `web-1`. + +```shell +kubectl get pvc -l app=nginx +NAME STATUS VOLUME CAPACITY ACCESSMODES AGE +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/user-guide/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 +backed by a PersistentVolume. + +Write the Pods' hostnames to their `index.html` files and verify that the NGINX +webservers serve the hostnames. + +```shell +for i in 0 1; do kubectl exec web-$i -- sh -c 'echo $(hostname) > /usr/share/nginx/html/index.html'; done + +for i in 0 1; do kubectl exec -it web-$i -- curl localhost; done +web-0 +web-1 +``` + +In one terminal, watch the StatefulSet's Pods. + +```shell +kubectl get pod -w -l app=nginx +``` + +In a second terminal, delete all of the StatefulSet's Pods. + +```shell +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 +for all of the Pods to transition to Running and Ready. + +```shell +kubectl get pod -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 0/1 ContainerCreating 0 0s +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 2s +web-1 0/1 Pending 0 0s +web-1 0/1 Pending 0 0s +web-1 0/1 ContainerCreating 0 0s +web-1 1/1 Running 0 34s +``` + +Verify the web servers continue to serve their hostnames. + +``` +for i in 0 1; do kubectl exec -it web-$i -- curl localhost; done +web-0 +web-1 +``` + +Event though `web-0` and `web-1` were rescheduled, they continue to serve their +hostnames because the PersistentVolumes associated with their Persistent +Volume Claims are remounted to their `volumeMount`s. 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. +This is accomplished by updating the `replicas` field. You can use either +[`kubectl scale`](/docs/user-guide/kubectl/kubectl_scale/) or +[`kubectl patch`](/docs/user-guide/kubectl/kubectl_patch/) to scale a Stateful +Set. + +#### Scaling Up + +In one terminal window, watch the Pods in the StatefulSet. + +```shell +kubectl get pods -w -l app=nginx +``` + +In another terminal window, use `kubectl scale` to scale the number of replicas +to 5. + +```shell +kubectl scale statefulset web --replicas=5 +statefulset "web" scaled +``` + +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 +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 2h +web-1 1/1 Running 0 2h +NAME READY STATUS RESTARTS AGE +web-2 0/1 Pending 0 0s +web-2 0/1 Pending 0 0s +web-2 0/1 ContainerCreating 0 0s +web-2 1/1 Running 0 19s +web-3 0/1 Pending 0 0s +web-3 0/1 Pending 0 0s +web-3 0/1 ContainerCreating 0 0s +web-3 1/1 Running 0 18s +web-4 0/1 Pending 0 0s +web-4 0/1 Pending 0 0s +web-4 0/1 ContainerCreating 0 0s +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 +subsequent Pod. + +#### Scaling Down + +In one terminal, watch the StatefulSet's Pods. + +```shell +kubectl get pods -w -l app=nginx +``` + +In another terminal, use `kubectl patch` to scale the StatefulSet back down to +3 replicas. + +```shell +kubectl patch statefulset web -p '{"spec":{"replicas":3}}' +"web" patched +``` + +Wait for `web-4` and `web-3` to transition to Terminating. + +``` +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 3h +web-1 1/1 Running 0 3h +web-2 1/1 Running 0 55s +web-3 1/1 Running 0 36s +web-4 0/1 ContainerCreating 0 18s +NAME READY STATUS RESTARTS AGE +web-4 1/1 Running 0 19s +web-4 1/1 Terminating 0 24s +web-4 1/1 Terminating 0 24s +web-3 1/1 Terminating 0 42s +web-3 1/1 Terminating 0 42s +``` + +#### Ordered Pod Termination + +The controller deleted one Pod at a time, with respect to its ordinal index, +in reverse order, and it waited for each to be completely shutdown before +deleting the next. + +Get the StatefulSet's PersistentVolumeClaims. + +```shell +kubectl get pvc -l app=nginx +NAME STATUS VOLUME CAPACITY ACCESSMODES AGE +www-web-0 Bound pvc-15c268c7-b507-11e6-932f-42010a800002 1Gi RWO 13h +www-web-1 Bound pvc-15c79307-b507-11e6-932f-42010a800002 1Gi RWO 13h +www-web-2 Bound pvc-e1125b27-b508-11e6-932f-42010a800002 1Gi RWO 13h +www-web-3 Bound pvc-e1176df6-b508-11e6-932f-42010a800002 1Gi RWO 13h +www-web-4 Bound pvc-e11bb5f8-b508-11e6-932f-42010a800002 1Gi RWO 13h + +``` + +There are still five PersistentVolumeClaims and five PersistentVolumes. +When exploring a Pod's [stable storage](#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. This feature can be used to facilitate +upgrading the container images of Pods in a StatefulSet. + +### Updating Containers +As demonstrated in the [Scaling a StatefulSet](#scaling-a-statefulset) section, +the `replicas` field of a StatefulSet is mutable. The only other field of a +StatefulSet that can be updated is the `spec.template.containers` field. + +StatefulSet currently *does not* support automated image upgrade. However, you +can update the `image` field of any container in the podTemplate and delete +StatefulSet's Pods one by one, the StatefulSet controller will recreate +each Pod with the new image. + +Patch the container image for the `web` StatefulSet. + +```shell +kubectl patch statefulset web --type='json' -p='[{"op": "replace", "path": "/spec/template/spec/containers/0/image", "value":"gcr.io/google_containers/nginx-slim:0.7"}]' +"web" patched +``` + +Delete the `web-0` Pod. + +```shell +kubectl delete pod web-0 +pod "web-0" deleted +``` + +Watch `web-0`, and wait for the Pod to transition to Running and Ready. + +```shell +kubectl get pod web-0 -w +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 54s +web-0 1/1 Terminating 0 1m +web-0 0/1 Terminating 0 1m +web-0 0/1 Terminating 0 1m +web-0 0/1 Terminating 0 1m +web-0 0/1 Pending 0 0s +web-0 0/1 Pending 0 0s +web-0 0/1 ContainerCreating 0 0s +web-0 1/1 Running 0 3s +``` + +Get the Pods to view their container images. + +```shell{% raw %} +for p in 0 1 2; do kubectl get po web-$p --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'; echo; done +gcr.io/google_containers/nginx-slim:0.7 +gcr.io/google_containers/nginx-slim:0.8 +gcr.io/google_containers/nginx-slim:0.8 +{% endraw %}``` + +`web-0` has had its image updated. Complete the update by deleting the remaining +Pods. + +```shell +kubectl delete pod web-1 web-2 +pod "web-1" deleted +pod "web-2" deleted +``` + +Watch the Pods, and wait for all of them to transition to Running and Ready. + +``` +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 8m +web-1 1/1 Running 0 4h +web-2 1/1 Running 0 23m +NAME READY STATUS RESTARTS AGE +web-1 1/1 Terminating 0 4h +web-1 1/1 Terminating 0 4h +web-1 0/1 Pending 0 0s +web-1 0/1 Pending 0 0s +web-1 0/1 ContainerCreating 0 0s +web-2 1/1 Terminating 0 23m +web-2 1/1 Terminating 0 23m +web-1 1/1 Running 0 4s +web-2 0/1 Pending 0 0s +web-2 0/1 Pending 0 0s +web-2 0/1 ContainerCreating 0 0s +web-2 1/1 Running 0 36s +``` + +Get the Pods to view their container images. + +```shell{% raw %} +for p in 0 1 2; do kubectl get po web-$p --template '{{range $i, $c := .spec.containers}}{{$c.image}}{{end}}'; echo; done +gcr.io/google_containers/nginx-slim:0.7 +gcr.io/google_containers/nginx-slim:0.7 +gcr.io/google_containers/nginx-slim:0.7 +{% endraw %}``` + +All the Pods in the StatefulSet are now running a new container image. + +### Deleting StatefulSets + +StatefulSet supports both Non-Cascading and Cascading deletion. In a +Non-Cascading Delete, the StatefulSet's Pods are not deleted when the Stateful +Set is deleted. In a Cascading Delete, both the StatefulSet and its Pods are +deleted. + +#### Non-Cascading Delete + +In one terminal window, watch the Pods in the StatefulSet. + +``` +kubectl get pods -w -l app=nginx +``` + +Use [`kubectl delete`](/docs/user-guide/kubectl/kubectl_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 +kubectl delete statefulset web --cascade=false +statefulset "web" deleted +``` + +Get the Pods to examine their status. + +```shell +kubectl get pods -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 6m +web-1 1/1 Running 0 7m +web-2 1/1 Running 0 5m +``` + +Even though `web` has been deleted, all of the Pods are still Running and Ready. +Delete `web-0`. + +```shell +kubectl delete pod web-0 +pod "web-0" deleted +``` + +Get the StatefulSet's Pods. + +```shell +kubectl get pods -l app=nginx +NAME READY STATUS RESTARTS AGE +web-1 1/1 Running 0 10m +web-2 1/1 Running 0 7m +``` + +As the `web` StatefulSet has been deleted, `web-0` has not been relaunched. + +In one terminal, watch the StatefulSet's Pods. + +``` +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 +an error indicating that the Service already exists. + +```shell +kubectl create -f web.yaml +statefulset "web" created +Error from server (AlreadyExists): error when creating "web.yaml": services "nginx" already exists +``` + +Ignore the error. It only indicates that an attempt was made to create the nginx +Headless Service even though that Service already exists. + +Examine the output of the `kubectl get` command running in the first terminal. + +```shell +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-1 1/1 Running 0 16m +web-2 1/1 Running 0 2m +NAME READY STATUS RESTARTS AGE +web-0 0/1 Pending 0 0s +web-0 0/1 Pending 0 0s +web-0 0/1 ContainerCreating 0 0s +web-0 1/1 Running 0 18s +web-2 1/1 Terminating 0 3m +web-2 0/1 Terminating 0 3m +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`. +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. + +Let's take another look at the contents of the `index.html` file served by the +Pods' webservers. + +```shell +for i in 0 1; do kubectl exec -it web-$i -- curl localhost; done +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 +PersistentVolume was remounted. + +#### Cascading Delete + +In one terminal window, watch the Pods in the StatefulSet. + +```shell +kubectl get pods -w -l app=nginx +``` + +In another terminal, delete the StatefulSet again. This time, omit the +`--cascade=false` parameter. + +```shell +kubectl delete statefulset web +statefulset "web" deleted +``` +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 +kubectl get pods -w -l app=nginx +NAME READY STATUS RESTARTS AGE +web-0 1/1 Running 0 11m +web-1 1/1 Running 0 27m +NAME READY STATUS RESTARTS AGE +web-0 1/1 Terminating 0 12m +web-1 1/1 Terminating 0 29m +web-0 0/1 Terminating 0 12m +web-0 0/1 Terminating 0 12m +web-0 0/1 Terminating 0 12m +web-1 0/1 Terminating 0 29m +web-1 0/1 Terminating 0 29m +web-1 0/1 Terminating 0 29m + +``` + +As you saw in the [Scaling Down](#ordered-pod-termination) 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, +it will not delete the Headless Service associated with the StatefulSet. You +must delete the `nginx` Service manually. + +```shell +kubectl delete service nginx +service "nginx" deleted +``` + +Recreate the StatefulSet and Headless Service one more time. + +```shell +kubectl create -f web.yaml +service "nginx" created +statefulset "web" created +``` + +When all of the StatefulSet's Pods transition to Running and Ready, retrieve +the contents of their `index.html` files. + +```shell +for i in 0 1; do kubectl exec -it web-$i -- curl localhost; done +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 +`web-1` will still serve their hostnames. + +Finally delete the `web` StatefulSet and the `nginx` service. + +```shell +kubectl delete service nginx +service "nginx" deleted + +kubectl delete statefulset web +statefulset "web" deleted +``` + +{% endcapture %} + +{% capture 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 +reclaimed. +{% endcapture %} + +{% include templates/tutorial.md %} \ No newline at end of file diff --git a/docs/tutorials/stateful-application/web.yaml b/docs/tutorials/stateful-application/web.yaml new file mode 100644 index 0000000000..a583d52655 --- /dev/null +++ b/docs/tutorials/stateful-application/web.yaml @@ -0,0 +1,47 @@ +--- +apiVersion: v1 +kind: Service +metadata: + name: nginx + labels: + app: nginx +spec: + ports: + - port: 80 + name: web + clusterIP: None + selector: + app: nginx +--- +apiVersion: apps/v1beta1 +kind: StatefulSet +metadata: + name: web +spec: + serviceName: "nginx" + replicas: 2 + template: + metadata: + labels: + app: nginx + spec: + containers: + - name: nginx + image: gcr.io/google_containers/nginx-slim:0.8 + ports: + - containerPort: 80 + name: web + volumeMounts: + - name: www + mountPath: /usr/share/nginx/html + volumeClaimTemplates: + - metadata: + name: www + annotations: + volume.alpha.kubernetes.io/storage-class: anything + spec: + accessModes: [ "ReadWriteOnce" ] + resources: + requests: + storage: 1Gi +