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‎content/ja/docs/tutorials/stateful-application/cassandra.md

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---
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title: "Example: Deploying Cassandra with a StatefulSet"
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reviewers:
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- ahmetb
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content_type: tutorial
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weight: 30
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---
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<!-- overview -->
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This tutorial shows you how to run [Apache Cassandra](http://cassandra.apache.org/) on Kubernetes. Cassandra, a database, needs persistent storage to provide data durability (application _state_). In this example, a custom Cassandra seed provider lets the database discover new Cassandra instances as they join the Cassandra cluster.
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*StatefulSets* make it easier to deploy stateful applications into your Kubernetes cluster. For more information on the features used in this tutorial, see [StatefulSet](/docs/concepts/workloads/controllers/statefulset/).
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{{< note >}}
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Cassandra and Kubernetes both use the term _node_ to mean a member of a cluster. In this
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tutorial, the Pods that belong to the StatefulSet are Cassandra nodes and are members
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of the Cassandra cluster (called a _ring_). When those Pods run in your Kubernetes cluster,
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the Kubernetes control plane schedules those Pods onto Kubernetes
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{{< glossary_tooltip text="Nodes" term_id="node" >}}.
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When a Cassandra node starts, it uses a _seed list_ to bootstrap discovery of other
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nodes in the ring.
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This tutorial deploys a custom Cassandra seed provider that lets the database discover
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new Cassandra Pods as they appear inside your Kubernetes cluster.
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{{< /note >}}
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## {{% heading "objectives" %}}
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* Create and validate a Cassandra headless {{< glossary_tooltip text="Service" term_id="service" >}}.
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* Use a {{< glossary_tooltip term_id="StatefulSet" >}} to create a Cassandra ring.
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* Validate the StatefulSet.
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* Modify the StatefulSet.
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* Delete the StatefulSet and its {{< glossary_tooltip text="Pods" term_id="pod" >}}.
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## {{% heading "prerequisites" %}}
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{{< include "task-tutorial-prereqs.md" >}}
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To complete this tutorial, you should already have a basic familiarity with {{< glossary_tooltip text="Pods" term_id="pod" >}}, {{< glossary_tooltip text="Services" term_id="service" >}}, and {{< glossary_tooltip text="StatefulSets" term_id="StatefulSet" >}}.
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### Additional Minikube setup instructions
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{{< caution >}}
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[Minikube](/docs/getting-started-guides/minikube/) defaults to 1024MiB of memory and 1 CPU. Running Minikube with the default resource configuration results in insufficient resource errors during this tutorial. To avoid these errors, start Minikube with the following settings:
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```shell
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minikube start --memory 5120 --cpus=4
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```
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{{< /caution >}}
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<!-- lessoncontent -->
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## Creating a headless Service for Cassandra {#creating-a-cassandra-headless-service}
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In Kubernetes, a {{< glossary_tooltip text="Service" term_id="service" >}} describes a set of {{< glossary_tooltip text="Pods" term_id="pod" >}} that perform the same task.
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The following Service is used for DNS lookups between Cassandra Pods and clients within your cluster:
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{{< codenew file="application/cassandra/cassandra-service.yaml" >}}
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Create a Service to track all Cassandra StatefulSet members from the `cassandra-service.yaml` file:
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```shell
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kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-service.yaml
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```
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### Validating (optional) {#validating}
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Get the Cassandra Service.
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```shell
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kubectl get svc cassandra
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```
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The response is
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```
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NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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cassandra ClusterIP None <none> 9042/TCP 45s
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```
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If you don't see a Service named `cassandra`, that means creation failed. Read [Debug Services](/docs/tasks/debug-application-cluster/debug-service/) for help troubleshooting common issues.
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## Using a StatefulSet to create a Cassandra ring
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The StatefulSet manifest, included below, creates a Cassandra ring that consists of three Pods.
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{{< note >}}
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This example uses the default provisioner for Minikube. Please update the following StatefulSet for the cloud you are working with.
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{{< /note >}}
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{{< codenew file="application/cassandra/cassandra-statefulset.yaml" >}}
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Create the Cassandra StatefulSet from the `cassandra-statefulset.yaml` file:
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```shell
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# Use this if you are able to apply cassandra-statefulset.yaml unmodified
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kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml
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```
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If you need to modify `cassandra-statefulset.yaml` to suit your cluster, download
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https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml and then apply
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that manifest, from the folder you saved the modified version into:
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```shell
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# Use this if you needed to modify cassandra-statefulset.yaml locally
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kubectl apply -f cassandra-statefulset.yaml
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```
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## Validating the Cassandra StatefulSet
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1. Get the Cassandra StatefulSet:
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```shell
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kubectl get statefulset cassandra
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```
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The response should be similar to:
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```
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NAME DESIRED CURRENT AGE
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cassandra 3 0 13s
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```
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The `StatefulSet` resource deploys Pods sequentially.
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1. Get the Pods to see the ordered creation status:
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```shell
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kubectl get pods -l="app=cassandra"
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```
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The response should be similar to:
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```shell
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NAME READY STATUS RESTARTS AGE
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cassandra-0 1/1 Running 0 1m
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cassandra-1 0/1 ContainerCreating 0 8s
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```
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It can take several minutes for all three Pods to deploy. Once they are deployed, the same command
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returns output similar to:
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```
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NAME READY STATUS RESTARTS AGE
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cassandra-0 1/1 Running 0 10m
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cassandra-1 1/1 Running 0 9m
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cassandra-2 1/1 Running 0 8m
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```
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3. Run the Cassandra [nodetool](https://cwiki.apache.org/confluence/display/CASSANDRA2/NodeTool) inside the first Pod, to
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display the status of the ring.
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```shell
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kubectl exec -it cassandra-0 -- nodetool status
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```
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The response should look something like:
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```
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Datacenter: DC1-K8Demo
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======================
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Status=Up/Down
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|/ State=Normal/Leaving/Joining/Moving
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-- Address Load Tokens Owns (effective) Host ID Rack
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UN 172.17.0.5 83.57 KiB 32 74.0% e2dd09e6-d9d3-477e-96c5-45094c08db0f Rack1-K8Demo
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UN 172.17.0.4 101.04 KiB 32 58.8% f89d6835-3a42-4419-92b3-0e62cae1479c Rack1-K8Demo
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UN 172.17.0.6 84.74 KiB 32 67.1% a6a1e8c2-3dc5-4417-b1a0-26507af2aaad Rack1-K8Demo
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```
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## Modifying the Cassandra StatefulSet
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Use `kubectl edit` to modify the size of a Cassandra StatefulSet.
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1. Run the following command:
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```shell
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kubectl edit statefulset cassandra
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```
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This command opens an editor in your terminal. The line you need to change is the `replicas` field. The following sample is an excerpt of the StatefulSet file:
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```yaml
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# Please edit the object below. Lines beginning with a '#' will be ignored,
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# and an empty file will abort the edit. If an error occurs while saving this file will be
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# reopened with the relevant failures.
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#
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apiVersion: apps/v1
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kind: StatefulSet
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metadata:
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creationTimestamp: 2016-08-13T18:40:58Z
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generation: 1
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labels:
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app: cassandra
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name: cassandra
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namespace: default
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resourceVersion: "323"
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uid: 7a219483-6185-11e6-a910-42010a8a0fc0
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spec:
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replicas: 3
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```
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1. Change the number of replicas to 4, and then save the manifest.
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The StatefulSet now scales to run with 4 Pods.
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1. Get the Cassandra StatefulSet to verify your change:
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```shell
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kubectl get statefulset cassandra
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```
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The response should be similar to:
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```
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NAME DESIRED CURRENT AGE
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cassandra 4 4 36m
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```
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## {{% heading "cleanup" %}}
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Deleting or scaling a StatefulSet down does not delete the volumes associated with the StatefulSet. This setting is for your safety because your data is more valuable than automatically purging all related StatefulSet resources.
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{{< warning >}}
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Depending on the storage class and reclaim policy, deleting the *PersistentVolumeClaims* may cause the associated volumes to also be deleted. Never assume you’ll be able to access data if its volume claims are deleted.
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{{< /warning >}}
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1. Run the following commands (chained together into a single command) to delete everything in the Cassandra StatefulSet:
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```shell
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grace=$(kubectl get pod cassandra-0 -o=jsonpath='{.spec.terminationGracePeriodSeconds}') \
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&& kubectl delete statefulset -l app=cassandra \
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&& echo "Sleeping ${grace} seconds" 1>&2 \
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&& sleep $grace \
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&& kubectl delete persistentvolumeclaim -l app=cassandra
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```
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1. Run the following command to delete the Service you set up for Cassandra:
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```shell
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kubectl delete service -l app=cassandra
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```
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## Cassandra container environment variables
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The Pods in this tutorial use the [`gcr.io/google-samples/cassandra:v13`](https://github.com/kubernetes/examples/blob/master/cassandra/image/Dockerfile)
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image from Google's [container registry](https://cloud.google.com/container-registry/docs/).
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The Docker image above is based on [debian-base](https://github.com/kubernetes/kubernetes/tree/master/build/debian-base)
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and includes OpenJDK 8.
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This image includes a standard Cassandra installation from the Apache Debian repo.
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By using environment variables you can change values that are inserted into `cassandra.yaml`.
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| Environment variable | Default value |
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| ------------------------ |:---------------: |
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| `CASSANDRA_CLUSTER_NAME` | `'Test Cluster'` |
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| `CASSANDRA_NUM_TOKENS` | `32` |
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| `CASSANDRA_RPC_ADDRESS` | `0.0.0.0` |
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## {{% heading "whatsnext" %}}
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* Learn how to [Scale a StatefulSet](/docs/tasks/run-application/scale-stateful-set/).
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* Learn more about the [*KubernetesSeedProvider*](https://github.com/kubernetes/examples/blob/master/cassandra/java/src/main/java/io/k8s/cassandra/KubernetesSeedProvider.java)
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* See more custom [Seed Provider Configurations](https://git.k8s.io/examples/cassandra/java/README.md)
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