From ded8bdb23850cbafdc37b2f0599b2ab6253ec10b Mon Sep 17 00:00:00 2001 From: Tim Bannister Date: Sun, 8 Dec 2019 18:11:39 +0000 Subject: [PATCH] Update Casandra StatefulSet tutorial MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit * Retitle to use StatefulSet term * Use full name: Apache Cassandra * Always use StatefulSet from apps/v1 * (It's safe to assume readers are using Kubernetes ≥ v1.9) * Update to match website style guidelines * Move note about environment variables out of overview * Tweak wording for clarity & tidy whitespace * Tweak chained shell commands for clarity * Drop duplicated / unnecessary task prerequisites --- .../stateful-application/cassandra.md | 172 ++++++++++-------- 1 file changed, 93 insertions(+), 79 deletions(-) diff --git a/content/en/docs/tutorials/stateful-application/cassandra.md b/content/en/docs/tutorials/stateful-application/cassandra.md index a20d93926d..f55a852abb 100644 --- a/content/en/docs/tutorials/stateful-application/cassandra.md +++ b/content/en/docs/tutorials/stateful-application/cassandra.md @@ -1,5 +1,5 @@ --- -title: "Example: Deploying Cassandra with Stateful Sets" +title: "Example: Deploying Cassandra with a StatefulSet" reviewers: - ahmetb content_template: templates/tutorial @@ -7,79 +7,66 @@ weight: 30 --- {{% capture overview %}} -This tutorial shows you how to develop a native cloud [Cassandra](http://cassandra.apache.org/) deployment on Kubernetes. In this example, a custom Cassandra *SeedProvider* enables Cassandra to discover new Cassandra nodes as they join the cluster. +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. -*StatefulSets* make it easier to deploy stateful applications within a clustered environment. For more information on the features used in this tutorial, see the [*StatefulSet*](/docs/concepts/workloads/controllers/statefulset/) documentation. +*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/). -**Cassandra on Docker** - -The *Pods* in this tutorial 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` | +{{< note >}} +Cassandra and Kubernetes both use the term _node_ to mean a member of a cluster. In this +tutorial, the Pods that belong to the StatefulSet are Cassandra nodes and are members +of the Cassandra cluster (called a _ring_). When those Pods run in your Kubernetes cluster, +the Kubernetes control plane schedules those Pods onto Kubernetes +{{< glossary_tooltip text="Nodes" term_id="node" >}}. +When a Cassandra node starts, it uses a _seed list_ to bootstrap discovery of other +nodes in the ring. +This tutorial deploys a custom Cassandra seed provider that lets the database discover +new Cassandra Pods as they appear inside your Kubernetes cluster. +{{< /note >}} {{% /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/). +* Create and validate a Cassandra headless {{< glossary_tooltip text="Service" term_id="service" >}}. +* Use a {{< glossary_tooltip term_id="StatefulSet" >}} to create a Cassandra ring. +* Validate the StatefulSet. +* Modify the StatefulSet. +* Delete the StatefulSet and its {{< glossary_tooltip text="Pods" term_id="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: +{{< include "task-tutorial-prereqs.md" >}} -* [Install and Configure](/docs/tasks/tools/install-kubectl/) the *kubectl* command-line tool +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" >}}. -* Download [`cassandra-service.yaml`](/examples/application/cassandra/cassandra-service.yaml) - and [`cassandra-statefulset.yaml`](/examples/application/cassandra/cassandra-statefulset.yaml) - -* Have a supported Kubernetes cluster running - -{{< note >}} -Please read the [setup](/docs/setup/) if you do not already have a cluster. -{{< /note >}} - -### Additional Minikube Setup Instructions +### Additional Minikube setup instructions {{< caution >}} -[Minikube](/docs/getting-started-guides/minikube/) defaults to 1024MB 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: +[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: ```shell minikube start --memory 5120 --cpus=4 ``` {{< /caution >}} - + {{% /capture %}} {{% capture lessoncontent %}} -## Creating a Cassandra Headless Service +## Creating a headless Service for Cassandra {#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. +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. -The following `Service` is used for DNS lookups between Cassandra Pods and clients within the Kubernetes cluster. +The following Service is used for DNS lookups between Cassandra Pods and clients within your cluster: {{< codenew file="application/cassandra/cassandra-service.yaml" >}} -1. Launch a terminal window in the directory you downloaded the manifest files. -1. Create a Service to track all Cassandra StatefulSet nodes from the `cassandra-service.yaml` file: +Create a Service to track all Cassandra StatefulSet members from the `cassandra-service.yaml` file: - ```shell - kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-service.yaml - ``` +```shell +kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-service.yaml +``` -### Validating (optional) + +### Validating (optional) {#validating} Get the Cassandra Service. @@ -94,9 +81,9 @@ NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE cassandra ClusterIP None 9042/TCP 45s ``` -Service creation failed if anything else is returned. Read [Debug Services](/docs/tasks/debug-application-cluster/debug-service/) for common issues. +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. -## Using a StatefulSet to Create a Cassandra Ring +## Using a StatefulSet to create a Cassandra ring The StatefulSet manifest, included below, creates a Cassandra ring that consists of three Pods. @@ -106,14 +93,23 @@ This example uses the default provisioner for Minikube. Please update the follow {{< codenew file="application/cassandra/cassandra-statefulset.yaml" >}} -1. Update the StatefulSet if necessary. -1. Create the Cassandra StatefulSet from the `cassandra-statefulset.yaml` file: +Create the Cassandra StatefulSet from the `cassandra-statefulset.yaml` file: - ```shell - kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml - ``` +```shell +# Use this if you are able to apply cassandra-statefulset.yaml unmodified +kubectl apply -f https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml +``` -## Validating The Cassandra StatefulSet +If you need to modify `cassandra-statefulset.yaml` to suit your cluster, download +https://k8s.io/examples/application/cassandra/cassandra-statefulset.yaml and then apply +that manifest, from the folder you saved the modified version into: +```shell +# Use this if you needed to modify cassandra-statefulset.yaml locally +kubectl apply -f cassandra-statefulset.yaml +``` + + +## Validating the Cassandra StatefulSet 1. Get the Cassandra StatefulSet: @@ -121,31 +117,32 @@ This example uses the default provisioner for Minikube. Please update the follow kubectl get statefulset cassandra ``` - The response should be: + The response should be similar to: ``` NAME DESIRED CURRENT AGE cassandra 3 0 13s ``` - The `StatefulSet` resource deploys Pods sequentially. + The `StatefulSet` resource deploys Pods sequentially. 1. Get the Pods to see the ordered creation status: ```shell kubectl get pods -l="app=cassandra" ``` - - The response should be: - + + The response should be similar to: + ```shell NAME READY STATUS RESTARTS AGE cassandra-0 1/1 Running 0 1m cassandra-1 0/1 ContainerCreating 0 8s ``` - - It can take several minutes for all three Pods to deploy. Once they are deployed, the same command returns: - + + It can take several minutes for all three Pods to deploy. Once they are deployed, the same command + returns output similar to: + ``` NAME READY STATUS RESTARTS AGE cassandra-0 1/1 Running 0 10m @@ -153,13 +150,14 @@ This example uses the default provisioner for Minikube. Please update the follow 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. +3. Run the Cassandra [nodetool](https://cwiki.apache.org/confluence/display/CASSANDRA2/NodeTool) inside the first Pod, to + display the status of the ring. ```shell kubectl exec -it cassandra-0 -- nodetool status ``` - The response should look something like this: + The response should look something like: ``` Datacenter: DC1-K8Demo @@ -174,7 +172,7 @@ This example uses the default provisioner for Minikube. Please update the follow ## Modifying the Cassandra StatefulSet -Use `kubectl edit` to modify the size of a Cassandra StatefulSet. +Use `kubectl edit` to modify the size of a Cassandra StatefulSet. 1. Run the following command: @@ -182,14 +180,14 @@ Use `kubectl edit` to modify the size of a Cassandra StatefulSet. kubectl edit statefulset cassandra ``` - 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: + 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: ```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 + apiVersion: apps/v1 kind: StatefulSet metadata: creationTimestamp: 2016-08-13T18:40:58Z @@ -204,50 +202,66 @@ Use `kubectl edit` to modify the size of a Cassandra StatefulSet. replicas: 3 ``` -1. Change the number of replicas to 4, and then save the manifest. +1. Change the number of replicas to 4, and then save the manifest. - The `StatefulSet` now contains 4 Pods. + The StatefulSet now scales to run with 4 Pods. -1. Get the Cassandra StatefulSet to verify: +1. Get the Cassandra StatefulSet to verify your change: ```shell kubectl get statefulset cassandra ``` - The response should be + The response should be similar to: ``` 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 setting is for your safety because your data is more valuable than automatically purging all related StatefulSet resources. +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. {{< 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`: +1. Run the following commands (chained together into a single command) to delete everything in the Cassandra StatefulSet: ```shell - grace=$(kubectl get po cassandra-0 -o=jsonpath='{.spec.terminationGracePeriodSeconds}') \ + grace=$(kubectl get pod cassandra-0 -o=jsonpath='{.spec.terminationGracePeriodSeconds}') \ && kubectl delete statefulset -l app=cassandra \ - && echo "Sleeping $grace" \ + && echo "Sleeping ${grace} seconds" 1>&2 \ && sleep $grace \ - && kubectl delete pvc -l app=cassandra + && kubectl delete persistentvolumeclaim -l app=cassandra ``` -1. Run the following command to delete the Cassandra Service. +1. Run the following command to delete the Service you set up for Cassandra: ```shell kubectl delete service -l app=cassandra ``` -{{% /capture %}} +## Cassandra container environment variables +The Pods in this tutorial 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`. + +| Environment variable | Default value | +| ------------------------ |:---------------: | +| `CASSANDRA_CLUSTER_NAME` | `'Test Cluster'` | +| `CASSANDRA_NUM_TOKENS` | `32` | +| `CASSANDRA_RPC_ADDRESS` | `0.0.0.0` | + + +{{% /capture %}} {{% capture whatsnext %}} * Learn how to [Scale a StatefulSet](/docs/tasks/run-application/scale-stateful-set/).