To practice kubernetes we need kubernetes, but it's a complex distributed system. For the learning purposes we use a special tool called kind - Kubernetes IN Docker.
"kind is a tool for running local Kubernetes clusters using Docker container "nodes". Kind was primarily designed for testing Kubernetes itself, but may be used for local development or CI. Please refer to Reference Documentation for more detailed instructions."
To make the workshop simple and useful for you, we prepared a special cloud training instance you should have received already. It's a linux-based virtual instance running in AWS with all the prerequisites installed:
- Docker (Docker is an open-source project that automates the deployment of software applications inside containers by providing an additional layer of abstraction and automation of OS-level virtualization on Linux.)
- Docker Compose (Docker Compose is a tool for defining and running multi-container Docker applications. It uses YAML files to configure the application's services and performs the creation and start-up process of all the containers with a single command. The docker-compose CLI utility allows users to run commands on multiple containers at once, for example, building images, scaling containers, running containers that were stopped, and more.)
- Kubernetes command-line tool, Kubectl (The Kubernetes command-line tool, kubectl, allows you to run commands against Kubernetes clusters. You can use kubectl to deploy applications, inspect and manage cluster resources, and view logs.)
watch(During the workshop some bootstrap can last for a few minutes and the utiltywatchhelps to see the evolutions.)- Kind (
kindis a tool for running local Kubernetes clusters using Docker container “nodes”.)
Let's check that the installation is successful. We will mark with a blue book the command (📘) and a green book (📗) to show expected result.
📘 Command to execute
# Check existing KinD clusters
kind get clusters📗 Expected output
kind-cassandra
📘 Execute the following command to list nodes in k8s cluster
kubectl get nodes📗 Expected output
NAME STATUS ROLES AGE VERSION
kind-cassandra-control-plane Ready master 2m4s v1.17.0
kind-cassandra-worker Ready <none> 86s v1.17.0
kind-cassandra-worker2 Ready <none> 88s v1.17.0
kind-cassandra-worker3 Ready <none> 88s v1.17.0
kind-cassandra-worker4 Ready <none> 88s v1.17.0
kind-cassandra-worker5 Ready <none> 88s v1.17.0
As you see, we have only one 'physical' node but 6-nodes Kubernetes cluster, 1 master and 5 workers.
Cass-operator is built to watch over pods running Casandra or DSE in a Kubernetes namespace. We need to create a namespace for the cluster. For the rest of this guide, we will be using the namespace cass-operator. You can pick any name you like but you would have to change the commands accordingly. We recommend to stick to the cass-operator namespace.
📘 Execute the following command to create the namespace
kubectl create ns cass-operator📗 Expected output
namespace/cass-operator created
Kubernetes uses the StorageClass resource as an abstraction layer between pods needing persistent storage and the storage resources that a specific Kubernetes cluster can provide. We recommend using the fastest type of networked storage available. Let's create one for your environment.
📘 Execute the following command to list existing storageClass
kubectl get storageclass📗 Expected output
NAME PROVISIONER RECLAIMPOLICY VOLUMEBINDINGMODE ALLOWVOLUMEEXPANSION AGE
standard (default) rancher.io/local-path Delete WaitForFirstConsumer false 11m📘 Execute the following command describe default storageClass
kubectl describe storageclass standard📗 Expected output (may vary)
Name: standard
IsDefaultClass: Yes
Annotations: kubectl.kubernetes.io/last-applied-configuration={"apiVersion":"storage.k8s.io/v1","kind":"StorageClass","metadata":{"annotations":{"storageclass.kubernetes.io/is-default-class":"true"},"name":"standard"},"provisioner":"rancher.io/local-path","reclaimPolicy":"Delete","volumeBindingMode":"WaitForFirstConsumer"}
,storageclass.kubernetes.io/is-default-class=true
Provisioner: rancher.io/local-path
Parameters: <none>
AllowVolumeExpansion: <unset>
MountOptions: <none>
ReclaimPolicy: Delete
VolumeBindingMode: WaitForFirstConsumer
Events: <none>
We are are interested in a few fields to intialize the yaml to create a storageClass. You can find more information in the Reference Documentation and the dedicated page to edit those.
One thing thing to note here is volumeBindingMode: WaitForFirstConsumer. The default value is Immediate and should not be used. It can prevent Cassandra pods from being scheduled on a worker node. If a pod fails to run and its status reports a message like, had volume node affinity conflict, then check the volumeBindingMode of the StorageClass being used
This file should be adapted tor reflect your Kubernetes environment. We have several samples in the repository for kind, Minikube and GKE.
apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
annotations:
storageclass.kubernetes.io/is-default-class: "true"
name: server-storage
provisioner: rancher.io/local-path
reclaimPolicy: Delete
volumeBindingMode: WaitForFirstConsumer📘 Execute the following command to create a new storageClass named server-storage
For the rest of this guide, we would assume you have defined a StorageClass and named it server-storage.
kubectl -n cass-operator apply -f ./0-setup-your-cluster-datastax/02-storageclass-kind.yaml📘 7e. Execute the following command to list the storageClass
kubectl -n cass-operator get storageClass
📗 Expected output
NAME PROVISIONER RECLAIMPOLICY VOLUMEBINDINGMODE ALLOWVOLUMEEXPANSION AGE
server-storage (default) rancher.io/local-path Delete WaitForFirstConsumer false 25m
standard (default) rancher.io/local-path Delete WaitForFirstConsumer false 88m
Please proceed to the next step!
