--- title: "Example: Deploying Cassandra with Stateful Sets" reviewers: - ahmetb content_template: templates/tutorial weight: 30 --- {{% capture overview %}} This tutorial shows you how to develop a native cloud [Cassandra](http://cassandra.apache.org/) deployment on Kubernetes. In this instance, a custom Cassandra `SeedProvider` enables Cassandra to discover new Cassandra nodes as they join the cluster. Deploying stateful distributed applications, like Cassandra, within a clustered environment can be challenging. StatefulSets greatly simplify this process. Please read about [StatefulSets](/docs/concepts/workloads/controllers/statefulset/) for more information about the features used in this tutorial. **Cassandra Docker** The Pods use the [`gcr.io/google-samples/cassandra:v13`](https://github.com/kubernetes/examples/blob/master/cassandra/image/Dockerfile) image from Google's [container registry](https://cloud.google.com/container-registry/docs/). The docker image above is based on [debian-base](https://github.com/kubernetes/kubernetes/tree/master/build/debian-base) and includes OpenJDK 8. This image includes a standard Cassandra installation from the Apache Debian repo. By using environment variables you can change values that are inserted into `cassandra.yaml`. | ENV VAR | DEFAULT VALUE | | ------------- |:-------------: | | `CASSANDRA_CLUSTER_NAME` | `'Test Cluster'` | | `CASSANDRA_NUM_TOKENS` | `32` | | `CASSANDRA_RPC_ADDRESS` | `0.0.0.0` | {{% /capture %}} {{% capture objectives %}} * Create and validate a Cassandra headless [Service](/docs/concepts/services-networking/service/). * Use a [StatefulSet](/docs/concepts/workloads/controllers/statefulset/) to create a Cassandra ring. * Validate the [StatefulSet](/docs/concepts/workloads/controllers/statefulset/). * Modify the [StatefulSet](/docs/concepts/workloads/controllers/statefulset/). * Delete the [StatefulSet](/docs/concepts/workloads/controllers/statefulset/) and its [Pods](/docs/concepts/workloads/pods/pod/). {{% /capture %}} {{% capture prerequisites %}} To complete this tutorial, you should already have a basic familiarity with [Pods](/docs/concepts/workloads/pods/pod/), [Services](/docs/concepts/services-networking/service/), and [StatefulSets](/docs/concepts/workloads/controllers/statefulset/). In addition, you should: * [Install and Configure](/docs/tasks/tools/install-kubectl/) the `kubectl` command line * Download [cassandra-service.yaml](/docs/tutorials/stateful-application/cassandra/cassandra-service.yaml) and [cassandra-statefulset.yaml](/docs/tutorials/stateful-application/cassandra/cassandra-statefulset.yaml) * Have a supported Kubernetes Cluster running {{< note >}} **Note:** Please read the [getting started guides](/docs/setup/pick-right-solution/) if you do not already have a cluster. {{< /note >}} ### Additional Minikube Setup Instructions {{< caution >}} **Caution:** [Minikube](/docs/getting-started-guides/minikube/) defaults to 1024MB of memory and 1 CPU. Running Minikube with the default resource configuration may result in insufficient resource errors during this tutorial. To avoid these errors, we recommend running Minikube with 5 GB of memory and 4 CPUs: ```bash minikube start --memory 5120 --cpus=4 ``` {{< /caution >}} {{% /capture %}} {{% capture lessoncontent %}} ## Creating a Cassandra Headless Service A Kubernetes [Service](/docs/concepts/services-networking/service/) describes a set of [Pods](/docs/concepts/workloads/pods/pod/) that perform the same task. The following `Service` is used for DNS lookups between Cassandra Pods and clients within the Kubernetes Cluster. 1. Launch a terminal window in the directory you downloaded the manifest files. 2. Create a `Service` to track all Cassandra StatefulSet Nodes from the `cassandra-service.yaml` file: ```bash kubectl create -f cassandra-service.yaml ``` {{< code file="cassandra/cassandra-service.yaml" >}} ### Validating (optional) Get the Cassandra `Service`. ```bash kubectl get svc cassandra ``` The response should be ``` NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE cassandra None 9042/TCP 45s ``` If anything else is returned, the Service was not successfully created. Read [Debug Services](/docs/tasks/debug-application-cluster/debug-service/) for common issues. ## Using a StatefulSet to Create a Cassandra Ring The StatefulSet manifest, included below, creates a Cassandra ring that consists of three Pods. {{< note >}} **Note:** This example uses the default provisioner for Minikube. Please update the following StatefulSet for the cloud you are working with. {{< /note >}} 1. Update the StatefulSet if necessary. 2. Create the Cassandra StatefulSet from the `cassandra-statefulset.yaml` file: ```bash kubectl create -f cassandra-statefulset.yaml ``` {{< code file="cassandra/cassandra-statefulset.yaml" >}} ## Validating The Cassandra StatefulSet 1. Get the Cassandra StatefulSet: ```bash kubectl get statefulset cassandra ``` The response should be: ``` NAME DESIRED CURRENT AGE cassandra 3 0 13s ``` The StatefulSet resource deploys Pods sequentially. 2. Get the Pods to see the ordered creation status: ```bash kubectl get pods -l="app=cassandra" ``` The response should be: ```bash NAME READY STATUS RESTARTS AGE cassandra-0 1/1 Running 0 1m cassandra-1 0/1 ContainerCreating 0 8s ``` Please note that it may take several minutes for all three Pods to deploy. Once they are deployed, the same command returns: ``` NAME READY STATUS RESTARTS AGE cassandra-0 1/1 Running 0 10m cassandra-1 1/1 Running 0 9m cassandra-2 1/1 Running 0 8m ``` 3. Run the Cassandra [nodetool](https://wiki.apache.org/cassandra/NodeTool) to display the status of the ring. ```bash kubectl exec -it cassandra-0 -- nodetool status ``` The response should look something like this: ``` Datacenter: DC1-K8Demo ====================== Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 172.17.0.5 83.57 KiB 32 74.0% e2dd09e6-d9d3-477e-96c5-45094c08db0f Rack1-K8Demo UN 172.17.0.4 101.04 KiB 32 58.8% f89d6835-3a42-4419-92b3-0e62cae1479c Rack1-K8Demo UN 172.17.0.6 84.74 KiB 32 67.1% a6a1e8c2-3dc5-4417-b1a0-26507af2aaad Rack1-K8Demo ``` ## Modifying the Cassandra StatefulSet Use `kubectl edit` to modify the size of a Cassandra StatefulSet. 1. Run the following command: ```bash kubectl edit statefulset cassandra ``` This command opens an editor in your terminal. The line you need to change is the `replicas` field. {{< note >}} **Note:** The following sample is an excerpt of the StatefulSet file. {{< /note >}} ```yaml # Please edit the object below. Lines beginning with a '#' will be ignored, # and an empty file will abort the edit. If an error occurs while saving this file will be # reopened with the relevant failures. # apiVersion: apps/v1 # for versions before 1.9.0 use apps/v1beta2 kind: StatefulSet metadata: creationTimestamp: 2016-08-13T18:40:58Z generation: 1 labels: app: cassandra name: cassandra namespace: default resourceVersion: "323" selfLink: /apis/apps/v1/namespaces/default/statefulsets/cassandra uid: 7a219483-6185-11e6-a910-42010a8a0fc0 spec: replicas: 3 ``` 2. Change the number of replicas to 4, and then save the manifest. The StatefulSet now contains 4 Pods. 3. Get the Cassandra StatefulSet to verify: ```bash kubectl get statefulset cassandra ``` The response should be ``` NAME DESIRED CURRENT AGE cassandra 4 4 36m ``` {{% /capture %}} {{% capture cleanup %}} Deleting or scaling a StatefulSet down does not delete the volumes associated with the StatefulSet. This ensures safety first: your data is more valuable than an auto purge of all related StatefulSet resources. {{< warning >}} **Warning:** 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. {{< /warning >}} 1. Run the following commands (chained together into a single command) to delete everything in the Cassandra StatefulSet: ```bash grace=$(kubectl get po cassandra-0 -o=jsonpath='{.spec.terminationGracePeriodSeconds}') \ && kubectl delete statefulset -l app=cassandra \ && echo "Sleeping $grace" \ && sleep $grace \ && kubectl delete pvc -l app=cassandra ``` 2. Run the following command to delete the Cassandra `Service`. ```bash kubectl delete service -l app=cassandra ``` {{% /capture %}} {{% capture whatsnext %}} * Learn how to [Scale a StatefulSet](/docs/tasks/run-application/scale-stateful-set/). * Learn more about the [KubernetesSeedProvider](https://github.com/kubernetes/examples/blob/master/cassandra/java/src/main/java/io/k8s/cassandra/KubernetesSeedProvider.java) * See more custom [Seed Provider Configurations](https://git.k8s.io/examples/cassandra/java/README.md) {{% /capture %}}