# Cloud Native Deployments of Cassandra using Kubernetes ## Table of Contents - [Prerequisites](#prerequisites) - [Cassandra Docker](#cassandra-docker) - [Quickstart](#quickstart) - [Step 1: Create a Cassandra Headless Service](#step-1-create-a-cassandra-headless-service) - [Step 2: Use a StatefulSet to create Cassandra Ring](#step-2-use-a-statefulset-to-create-cassandra-ring) - [Step 3: Validate and Modify The Cassandra StatefulSet](#step-3-validate-and-modify-the-cassandra-statefulset) - [Step 4: Delete Cassandra StatefulSet](#step-4-delete-cassandra-statefulset) - [Step 5: Use a Replication Controller to create Cassandra node pods](#step-5-use-a-replication-controller-to-create-cassandra-node-pods) - [Step 6: Scale up the Cassandra cluster](#step-6-scale-up-the-cassandra-cluster) - [Step 7: Delete the Replication Controller](#step-7-delete-the-replication-controller) - [Step 8: Use a DaemonSet instead of a Replication Controller](#step-8-use-a-daemonset-instead-of-a-replication-controller) - [Step 9: Resource Cleanup](#step-9-resource-cleanup) - [Seed Provider Source](#seed-provider-source) The following document describes the development of a _cloud native_ [Cassandra](http://cassandra.apache.org/) deployment on Kubernetes. When we say _cloud native_, we mean an application which understands that it is running within a cluster manager, and uses this cluster management infrastructure to help implement the application. In particular, in this instance, a custom Cassandra `SeedProvider` is used to enable Cassandra to dynamically discover new Cassandra nodes as they join the cluster. This example also uses some of the core components of Kubernetes: - [_Pods_](../../../docs/user-guide/pods.md) - [ _Services_](../../../docs/user-guide/services.md) - [_Replication Controllers_](../../../docs/user-guide/replication-controller.md) - [_Stateful Sets_](http://kubernetes.io/docs/user-guide/petset/) - [_Daemon Sets_](../../../docs/admin/daemons.md) ## Prerequisites This example assumes that you have a Kubernetes version >=1.2 cluster installed and running, and that you have installed the [`kubectl`](../../../docs/user-guide/kubectl/kubectl.md) command line tool somewhere in your path. Please see the [getting started guides](../../../docs/getting-started-guides/) for installation instructions for your platform. This example also has a few code and configuration files needed. To avoid typing these out, you can `git clone` the Kubernetes repository to your local computer. ## Cassandra Docker The pods use the [```gcr.io/google-samples/cassandra:v11```](image/Dockerfile) image from Google's [container registry](https://cloud.google.com/container-registry/docs/). The docker is based on `debian:jessie` and includes OpenJDK 8. This image includes a standard Cassandra installation from the Apache Debian repo. Through the use of environment variables you are able to change values that are inserted into the `cassandra.yaml`. | ENV VAR | DEFAULT VALUE | | ------------- |:-------------: | | CASSANDRA_CLUSTER_NAME | 'Test Cluster' | | CASSANDRA_NUM_TOKENS | 32 | | CASSANDRA_RPC_ADDRESS | 0.0.0.0 | ## Quickstart If you want to jump straight to the commands we will run, here are the steps: ```sh # # StatefulSet # # create a service to track all cassandra statefulset nodes kubectl create -f examples/storage/cassandra/cassandra-service.yaml # create a statefulset kubectl create -f examples/storage/cassandra/cassandra-statefulset.yaml # validate the Cassandra cluster. Substitute the name of one of your pods. kubectl exec -ti cassandra-0 -- nodetool status # cleanup grace=$(kubectl get po cassandra-0 --template '{{.spec.terminationGracePeriodSeconds}}') \ && kubectl delete statefulset,po -l app=cassandra \ && echo "Sleeping $grace" \ && sleep $grace \ && kubectl delete pvc -l app=cassandra # # Resource Controller Example # # create a replication controller to replicate cassandra nodes kubectl create -f examples/storage/cassandra/cassandra-controller.yaml # validate the Cassandra cluster. Substitute the name of one of your pods. kubectl exec -ti cassandra-xxxxx -- nodetool status # scale up the Cassandra cluster kubectl scale rc cassandra --replicas=4 # delete the replication controller kubectl delete rc cassandra # # Create a DaemonSet to place a cassandra node on each kubernetes node # kubectl create -f examples/storage/cassandra/cassandra-daemonset.yaml --validate=false # resource cleanup kubectl delete service -l app=cassandra kubectl delete daemonset cassandra ``` ## Step 1: Create a Cassandra Headless Service A Kubernetes _[Service](../../../docs/user-guide/services.md)_ describes a set of [_Pods_](../../../docs/user-guide/pods.md) that perform the same task. In Kubernetes, the atomic unit of an application is a Pod: one or more containers that _must_ be scheduled onto the same host. The Service is used for DNS lookups between Cassandra Pods, and Cassandra clients within the Kubernetes Cluster. Here is the service description: ```yaml apiVersion: v1 kind: Service metadata: labels: app: cassandra name: cassandra spec: clusterIP: None ports: - port: 9042 selector: app: cassandra ``` [Download example](cassandra-service.yaml?raw=true) Create the service for the StatefulSet: ```console $ kubectl create -f examples/storage/cassandra/cassandra-service.yaml ``` The following command shows if the service has been created. ```console $ kubectl get svc cassandra ``` The response should be like: ```console NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE cassandra None 9042/TCP 45s ``` If an error is returned the service create failed. ## Step 2: Use a StatefulSet to create Cassandra Ring StatefulSets (previously PetSets) are a new feature that was added as an Alpha component in Kubernetes 1.3. Deploying stateful distributed applications, like Cassandra, within a clustered environment can be challenging. We implemented StatefulSet to greatly simplify this process. Multiple StatefulSet features are used within this example, but is out of scope of this documentation. [Please refer to the PetSet documentation.](http://kubernetes.io/docs/user-guide/petset/) The StatefulSet manifest that is included below, creates a Cassandra ring that consists of three pods. ```yaml apiVersion: "apps/v1beta1" kind: StatefulSet metadata: name: cassandra spec: serviceName: cassandra replicas: 3 template: metadata: labels: app: cassandra spec: containers: - name: cassandra image: gcr.io/google-samples/cassandra:v11 imagePullPolicy: Always ports: - containerPort: 7000 name: intra-node - containerPort: 7001 name: tls-intra-node - containerPort: 7199 name: jmx - containerPort: 9042 name: cql resources: limits: cpu: "500m" memory: 1Gi requests: cpu: "500m" memory: 1Gi securityContext: capabilities: add: - IPC_LOCK env: - name: MAX_HEAP_SIZE value: 512M - name: HEAP_NEWSIZE value: 100M - name: CASSANDRA_SEEDS value: "cassandra-0.cassandra.default.svc.cluster.local" - name: CASSANDRA_CLUSTER_NAME value: "K8Demo" - name: CASSANDRA_DC value: "DC1-K8Demo" - name: CASSANDRA_RACK value: "Rack1-K8Demo" - name: CASSANDRA_AUTO_BOOTSTRAP value: "false" - name: POD_IP valueFrom: fieldRef: fieldPath: status.podIP readinessProbe: exec: command: - /bin/bash - -c - /ready-probe.sh initialDelaySeconds: 15 timeoutSeconds: 5 # These volume mounts are persistent. They are like inline claims, # but not exactly because the names need to match exactly one of # the stateful pod volumes. volumeMounts: - name: cassandra-data mountPath: /cassandra_data # These are converted to volume claims by the controller # and mounted at the paths mentioned above. # do not use these in production until ssd GCEPersistentDisk or other ssd pd volumeClaimTemplates: - metadata: name: cassandra-data annotations: volume.alpha.kubernetes.io/storage-class: anything spec: accessModes: [ "ReadWriteOnce" ] resources: requests: storage: 1Gi ``` [Download example](cassandra-statefulset.yaml?raw=true) Create the Cassandra StatefulSet as follows: ```console $ kubectl create -f examples/storage/cassandra/cassandra-statefulset.yaml ``` ## Step 3: Validate and Modify The Cassandra StatefulSet Deploying this StatefulSet shows off two of the new features that StatefulSets provides. 1. The pod names are known 2. The pods deploy in incremental order First validate that the StatefulSet has deployed, by running `kubectl` command below. ```console $ kubectl get statefulset cassandra ``` The command should respond like: ```console NAME DESIRED CURRENT AGE cassandra 3 3 13s ``` Next watch the Cassandra pods deploy, one after another. The StatefulSet resource deploys pods in a number fashion: 1, 2, 3, etc. If you execute the following command before the pods deploy you are able to see the ordered creation. ```console $ kubectl get pods -l="app=cassandra" NAME READY STATUS RESTARTS AGE cassandra-0 1/1 Running 0 1m cassandra-1 0/1 ContainerCreating 0 8s ``` The above example shows two of the three pods in the Cassandra StatefulSet deployed. Once all of the pods are deployed the same command will respond with the full StatefulSet. ```console $ kubectl get pods -l="app=cassandra" 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 ``` Running the Cassandra utility `nodetool` will display the status of the ring. ```console $ kubectl exec cassandra-0 -- nodetool status Datacenter: DC1-K8Demo ====================== Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 10.4.2.4 65.26 KiB 32 63.7% a9d27f81-6783-461d-8583-87de2589133e Rack1-K8Demo UN 10.4.0.4 102.04 KiB 32 66.7% 5559a58c-8b03-47ad-bc32-c621708dc2e4 Rack1-K8Demo UN 10.4.1.4 83.06 KiB 32 69.6% 9dce943c-581d-4c0e-9543-f519969cc805 Rack1-K8Demo ``` You can also run `cqlsh` to describe the keyspaces in the cluster. ```console $ kubectl exec cassandra-0 -- cqlsh -e 'desc keyspaces' system_traces system_schema system_auth system system_distributed ``` In order to increase or decrease the size of the Cassandra StatefulSet, you must use `kubectl edit`. You can find more information about the edit command in the [documentation](../../../docs/user-guide/kubectl/kubectl_edit.md). Use the following command to edit the StatefulSet. ```console $ kubectl edit statefulset cassandra ``` This will create an editor in your terminal. The line you are looking to change is `replicas`. The example does on contain the entire contents of the terminal window, and the last line of the example below is the replicas line that you want to change. ```console # 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/v1beta1 kind: StatefulSet metadata: creationTimestamp: 2016-08-13T18:40:58Z generation: 1 labels: app: cassandra name: cassandra namespace: default resourceVersion: "323" selfLink: /apis/apps/v1beta1/namespaces/default/statefulsets/cassandra uid: 7a219483-6185-11e6-a910-42010a8a0fc0 spec: replicas: 3 ``` Modify the manifest to the following, and save the manifest. ```console spec: replicas: 4 ``` The StatefulSet will now contain four pods. ```console $ kubectl get statefulset cassandra ``` The command should respond like: ```console NAME DESIRED CURRENT AGE cassandra 4 4 36m ``` For the Kubernetes 1.5 release, the beta StatefulSet resource does not have `kubectl scale` functionality, like a Deployment, ReplicaSet, Replication Controller, or Job. ## Step 4: Delete Cassandra StatefulSet Deleting and/or scaling a StatefulSet down will not delete the volumes associated with the StatefulSet. This is done to ensure safety first, your data is more valuable than an auto purge of all related StatefulSet resources. Deleting the Persistent Volume Claims may result in a deletion of the associated volumes, depending on the storage class and reclaim policy. You should never assume ability to access a volume after claim deletion. Use the following commands to delete the StatefulSet. ```console $ grace=$(kubectl get po cassandra-0 --template '{{.spec.terminationGracePeriodSeconds}}') \ && kubectl delete statefulset -l app=cassandra \ && echo "Sleeping $grace" \ && sleep $grace \ && kubectl delete pvc -l app=cassandra ``` ## Step 5: Use a Replication Controller to create Cassandra node pods A Kubernetes _[Replication Controller](../../../docs/user-guide/replication-controller.md)_ is responsible for replicating sets of identical pods. Like a Service, it has a selector query which identifies the members of its set. Unlike a Service, it also has a desired number of replicas, and it will create or delete Pods to ensure that the number of Pods matches up with its desired state. The Replication Controller, in conjunction with the Service we just defined, will let us easily build a replicated, scalable Cassandra cluster. Let's create a replication controller with two initial replicas. ```yaml apiVersion: v1 kind: ReplicationController metadata: name: cassandra # The labels will be applied automatically # from the labels in the pod template, if not set # labels: # app: cassandra spec: replicas: 2 # The selector will be applied automatically # from the labels in the pod template, if not set. # selector: # app: cassandra template: metadata: labels: app: cassandra spec: containers: - command: - /run.sh resources: limits: cpu: 0.5 env: - name: MAX_HEAP_SIZE value: 512M - name: HEAP_NEWSIZE value: 100M - name: CASSANDRA_SEED_PROVIDER value: "io.k8s.cassandra.KubernetesSeedProvider" - name: POD_NAMESPACE valueFrom: fieldRef: fieldPath: metadata.namespace - name: POD_IP valueFrom: fieldRef: fieldPath: status.podIP image: gcr.io/google-samples/cassandra:v11 name: cassandra ports: - containerPort: 7000 name: intra-node - containerPort: 7001 name: tls-intra-node - containerPort: 7199 name: jmx - containerPort: 9042 name: cql volumeMounts: - mountPath: /cassandra_data name: data volumes: - name: data emptyDir: {} ``` [Download example](cassandra-controller.yaml?raw=true) There are a few things to note in this description. The `selector` attribute contains the controller's selector query. It can be explicitly specified, or applied automatically from the labels in the pod template if not set, as is done here. The pod template's label, `app:cassandra`, matches the Service selector from Step 1. This is how pods created by this replication controller are picked up by the Service." The `replicas` attribute specifies the desired number of replicas, in this case 2 initially. We'll scale up to more shortly. Create the Replication Controller: ```console $ kubectl create -f examples/storage/cassandra/cassandra-controller.yaml ``` You can list the new controller: ```console $ kubectl get rc -o wide NAME DESIRED CURRENT AGE CONTAINER(S) IMAGE(S) SELECTOR cassandra 2 2 11s cassandra gcr.io/google-samples/cassandra:v11 app=cassandra ``` Now if you list the pods in your cluster, and filter to the label `app=cassandra`, you should see two Cassandra pods. (The `wide` argument lets you see which Kubernetes nodes the pods were scheduled onto.) ```console $ kubectl get pods -l="app=cassandra" -o wide NAME READY STATUS RESTARTS AGE NODE cassandra-21qyy 1/1 Running 0 1m kubernetes-minion-b286 cassandra-q6sz7 1/1 Running 0 1m kubernetes-minion-9ye5 ``` Because these pods have the label `app=cassandra`, they map to the service we defined in Step 1. You can check that the Pods are visible to the Service using the following service endpoints query: ```console $ kubectl get endpoints cassandra -o yaml apiVersion: v1 kind: Endpoints metadata: creationTimestamp: 2015-06-21T22:34:12Z labels: app: cassandra name: cassandra namespace: default resourceVersion: "944373" selfLink: /api/v1/namespaces/default/endpoints/cassandra uid: a3d6c25f-1865-11e5-a34e-42010af01bcc subsets: - addresses: - ip: 10.244.3.15 targetRef: kind: Pod name: cassandra namespace: default resourceVersion: "944372" uid: 9ef9895d-1865-11e5-a34e-42010af01bcc ports: - port: 9042 protocol: TCP ``` To show that the `SeedProvider` logic is working as intended, you can use the `nodetool` command to examine the status of the Cassandra cluster. To do this, use the `kubectl exec` command, which lets you run `nodetool` in one of your Cassandra pods. Again, substitute `cassandra-xxxxx` with the actual name of one of your pods. ```console $ kubectl exec -ti cassandra-xxxxx -- nodetool status Datacenter: datacenter1 ======================= Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 10.244.0.5 74.09 KB 256 100.0% 86feda0f-f070-4a5b-bda1-2eeb0ad08b77 rack1 UN 10.244.3.3 51.28 KB 256 100.0% dafe3154-1d67-42e1-ac1d-78e7e80dce2b rack1 ``` ## Step 6: Scale up the Cassandra cluster Now let's scale our Cassandra cluster to 4 pods. We do this by telling the Replication Controller that we now want 4 replicas. ```sh $ kubectl scale rc cassandra --replicas=4 ``` You can see the new pods listed: ```console $ kubectl get pods -l="app=cassandra" -o wide NAME READY STATUS RESTARTS AGE NODE cassandra-21qyy 1/1 Running 0 6m kubernetes-minion-b286 cassandra-81m2l 1/1 Running 0 47s kubernetes-minion-b286 cassandra-8qoyp 1/1 Running 0 47s kubernetes-minion-9ye5 cassandra-q6sz7 1/1 Running 0 6m kubernetes-minion-9ye5 ``` In a few moments, you can examine the Cassandra cluster status again, and see that the new pods have been detected by the custom `SeedProvider`: ```console $ kubectl exec -ti cassandra-xxxxx -- nodetool status Datacenter: datacenter1 ======================= Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 10.244.0.6 51.67 KB 256 48.9% d07b23a5-56a1-4b0b-952d-68ab95869163 rack1 UN 10.244.1.5 84.71 KB 256 50.7% e060df1f-faa2-470c-923d-ca049b0f3f38 rack1 UN 10.244.1.6 84.71 KB 256 47.0% 83ca1580-4f3c-4ec5-9b38-75036b7a297f rack1 UN 10.244.0.5 68.2 KB 256 53.4% 72ca27e2-c72c-402a-9313-1e4b61c2f839 rack1 ``` ## Step 7: Delete the Replication Controller Before you start Step 5, __delete the replication controller__ you created above: ```sh $ kubectl delete rc cassandra ``` ## Step 8: Use a DaemonSet instead of a Replication Controller In Kubernetes, a [_Daemon Set_](../../../docs/admin/daemons.md) can distribute pods onto Kubernetes nodes, one-to-one. Like a _ReplicationController_, it has a selector query which identifies the members of its set. Unlike a _ReplicationController_, it has a node selector to limit which nodes are scheduled with the templated pods, and replicates not based on a set target number of pods, but rather assigns a single pod to each targeted node. An example use case: when deploying to the cloud, the expectation is that instances are ephemeral and might die at any time. Cassandra is built to replicate data across the cluster to facilitate data redundancy, so that in the case that an instance dies, the data stored on the instance does not, and the cluster can react by re-replicating the data to other running nodes. `DaemonSet` is designed to place a single pod on each node in the Kubernetes cluster. That will give us data redundancy. Let's create a DaemonSet to start our storage cluster: ```yaml apiVersion: extensions/v1beta1 kind: DaemonSet metadata: labels: name: cassandra name: cassandra spec: template: metadata: labels: app: cassandra spec: # Filter to specific nodes: # nodeSelector: # app: cassandra containers: - command: - /run.sh env: - name: MAX_HEAP_SIZE value: 512M - name: HEAP_NEWSIZE value: 100M - name: CASSANDRA_SEED_PROVIDER value: "io.k8s.cassandra.KubernetesSeedProvider" - name: POD_NAMESPACE valueFrom: fieldRef: fieldPath: metadata.namespace - name: POD_IP valueFrom: fieldRef: fieldPath: status.podIP image: gcr.io/google-samples/cassandra:v11 name: cassandra ports: - containerPort: 7000 name: intra-node - containerPort: 7001 name: tls-intra-node - containerPort: 7199 name: jmx - containerPort: 9042 name: cql # If you need it it is going away in C* 4.0 #- containerPort: 9160 # name: thrift resources: requests: cpu: 0.5 volumeMounts: - mountPath: /cassandra_data name: data volumes: - name: data emptyDir: {} ``` [Download example](cassandra-daemonset.yaml?raw=true) Most of this DaemonSet definition is identical to the ReplicationController definition above; it simply gives the daemon set a recipe to use when it creates new Cassandra pods, and targets all Cassandra nodes in the cluster. Differentiating aspects are the `nodeSelector` attribute, which allows the DaemonSet to target a specific subset of nodes (you can label nodes just like other resources), and the lack of a `replicas` attribute due to the 1-to-1 node- pod relationship. Create this DaemonSet: ```console $ kubectl create -f examples/storage/cassandra/cassandra-daemonset.yaml ``` You may need to disable config file validation, like so: ```console $ kubectl create -f examples/storage/cassandra/cassandra-daemonset.yaml --validate=false ``` You can see the DaemonSet running: ```console $ kubectl get daemonset NAME DESIRED CURRENT NODE-SELECTOR cassandra 3 3 ``` Now, if you list the pods in your cluster, and filter to the label `app=cassandra`, you should see one (and only one) new cassandra pod for each node in your network. ```console $ kubectl get pods -l="app=cassandra" -o wide NAME READY STATUS RESTARTS AGE NODE cassandra-ico4r 1/1 Running 0 4s kubernetes-minion-rpo1 cassandra-kitfh 1/1 Running 0 1s kubernetes-minion-9ye5 cassandra-tzw89 1/1 Running 0 2s kubernetes-minion-b286 ``` To prove that this all worked as intended, you can again use the `nodetool` command to examine the status of the cluster. To do this, use the `kubectl exec` command to run `nodetool` in one of your newly-launched cassandra pods. ```console $ kubectl exec -ti cassandra-xxxxx -- nodetool status Datacenter: datacenter1 ======================= Status=Up/Down |/ State=Normal/Leaving/Joining/Moving -- Address Load Tokens Owns (effective) Host ID Rack UN 10.244.0.5 74.09 KB 256 100.0% 86feda0f-f070-4a5b-bda1-2eeb0ad08b77 rack1 UN 10.244.4.2 32.45 KB 256 100.0% 0b1be71a-6ffb-4895-ac3e-b9791299c141 rack1 UN 10.244.3.3 51.28 KB 256 100.0% dafe3154-1d67-42e1-ac1d-78e7e80dce2b rack1 ``` **Note**: This example had you delete the cassandra Replication Controller before you created the DaemonSet. This is because – to keep this example simple – the RC and the DaemonSet are using the same `app=cassandra` label (so that their pods map to the service we created, and so that the SeedProvider can identify them). If we didn't delete the RC first, the two resources would conflict with respect to how many pods they wanted to have running. If we wanted, we could support running both together by using additional labels and selectors. ## Step 9: Resource Cleanup When you are ready to take down your resources, do the following: ```console $ kubectl delete service -l app=cassandra $ kubectl delete daemonset cassandra ``` ### Custom Seed Provider A custom [`SeedProvider`](https://svn.apache.org/repos/asf/cassandra/trunk/src/java/org/apache/cassandra/locator/SeedProvider.java) is included for running Cassandra on top of Kubernetes. Only when you deploy Cassandra via a replication control or a deamonset, you will need to use the custom seed provider. In Cassandra, a `SeedProvider` bootstraps the gossip protocol that Cassandra uses to find other Cassandra nodes. Seed addresses are hosts deemed as contact points. Cassandra instances use the seed list to find each other and learn the topology of the ring. The [`KubernetesSeedProvider`](java/src/main/java/io/k8s/cassandra/KubernetesSeedProvider.java) discovers Cassandra seeds IP addresses via the Kubernetes API, those Cassandra instances are defined within the Cassandra Service. Refer to the custom seed provider [README](java/README.md) for further `KubernetesSeedProvider` configurations. For this example you should not need to customize the Seed Provider configurations. See the [image](image/) directory of this example for specifics on how the container docker image was built and what it contains. You may also note that we are setting some Cassandra parameters (`MAX_HEAP_SIZE` and `HEAP_NEWSIZE`), and adding information about the [namespace](../../../docs/user-guide/namespaces.md). We also tell Kubernetes that the container exposes both the `CQL` and `Thrift` API ports. Finally, we tell the cluster manager that we need 0.1 cpu (0.1 core). [![Analytics](https://kubernetes-site.appspot.com/UA-36037335-10/GitHub/examples/storage/cassandra/README.md?pixel)]()