Kubernetes

Kubernetes (/ˌk(j)uːbərˈnɛtɪs, -ˈneɪtɪs, -ˈneɪtiːz, -ˈnɛtiːz/, commonly abbreviated K8s) is an open-source container orchestration system for automating software deployment, scaling, and management. Originally designed by Google, the project is now maintained by the Cloud Native Computing Foundation.

The name Kubernetes originates from Greek, meaning 'helmsman' or 'pilot'. Kubernetes is often abbreviated as K8s, counting the eight letters between the K and the s (a numeronym).

Kubernetes works with containerd and CRI-O. Its suitability for running and managing large cloud-native workloads has led to widespread adoption of it in the data center. There are multiple distributions of this platform – from ISVs as well as hosted-on cloud offerings from all the major public cloud vendors.

Show all current pods

   kubectl get pods

Show current persistent volumes

   kubectl get pv

Show current persistent volume claims

   kubectl get pvc

Copy a file into a container of a pod

   kubectl cp start.sh pod1:/tmp/ -c container1

Execute a command within a container of a pod

   kubectl exec -it pod1 -c container1 -- /tmp/start.sh

Create a persistent volume for a pod to claim

Create the yaml first.

   echo "---
   apiVersion: v1
   kind: PersistentVolume
   metadata:
     name: persistentvolume01
   spec:
     accessModes:
       - ReadWriteOnce
     capacity:
       storage: 10Gi
     storageClassName: manual
     hostPath:
       path: /mnt/somedir" > persistentvolume01.yaml

Create the actual volume using the yaml:

   kubectl create -f persistentvolume01.yaml

Delete the persistent volume if necessary:

   kubectl delete -f persistentvolume01.yaml

Install Kubernetes to Ubuntu

The following commands will install microk8s to Ubuntu:

   sudo snap install microk8s --classic

Add your user to the microk8s admin group and fix permissions:

   sudo usermod -a -G microk8s $USER
   sudo chown -f -R $USER ~/.kube

Log out and log back in to that user for this to take effect.

Check the status of the service:

   microk8s status --wait-ready

Enable services:

   microk8s enable dashboard dns ingress metallb

Use the following to check for available services to enable:

   microk8s enable --help

Start using microk8s:

   microk8s kubectl get all --all-namespaces

Access the dashboard:

   microk8s dashboard-proxy

Clustering

To create a cluster out of two or more already-running MicroK8s instances, use the microk8s add-node command. As of MicroK8s 1.19, clustering of three or more nodes will automatically enable high availability. The MicroK8s instance on which the command is run will host the Kubernetes control plane:

   microk8s add-node

The add-node command prints a microk8s join command which should be executed on the MicroK8s instance(s) that you wish to join to the cluster (NOT THE NODE YOU RAN add-node FROM). For example:

   microk8s join ip-172-31-20-243:25000/DDOkUupkmaBezNnMheTBqFYHLWINGDbf

Joining a node to the cluster should only take a few seconds. Afterwards you should be able to see the node has joined:

   microk8s kubectl get no

Use NFS for Persistent Volumes

Provision NFS mounts as Kubernetes Persistent Volumes on MicroK8s.

NFS server

Either use a current NFS server or install a NFS server. The following is how to install to Ubuntu:

   apt install nfs-kernel-server

Directory /srv/nfs is the share folder.

   mkdir -p /srv/nfs
   chown nobody:nogroup /srv/nfs
   chmod 0777 /srv/nfs

Edit the /etc/exports. The following will allow all IP addresses in the 10.0.0.0/24 subnet:

   /srv/nfs 10.0.0.0/24(rw,sync,no_subtree_check)

Restart the NFS server:

   systemctl restart nfs-kernel-server

Install the CSI driver for NFS

Enable the Helm3 addon (if not already enabled) and add the repository for the NFS CSI driver:

   microk8s enable helm3
   microk8s helm3 repo add csi-driver-nfs https://raw.githubusercontent.com/kubernetes-csi/csi-driver-nfs/master/charts
   microk8s helm3 repo update

This will install the Helm chart under the kube-system namespace:

   microk8s helm3 install csi-driver-nfs csi-driver-nfs/csi-driver-nfs --namespace kube-system --set kubeletDir=/var/snap/microk8s/common/var/lib/kubelet

After deploying the Helm chart, wait for the CSI controller and node pods to come up using the following kubectl command:

   microk8s kubectl wait pod --selector app.kubernetes.io/name=csi-driver-nfs --for condition=ready --namespace kube-system

If successful, you will see "condition met". List the available CSI drivers in the Kubernetes cluster:

   microk8s kubectl get csidrivers

Create a StorageClass for NFS

This creates a Kubernetes Storage Class which uses the nfs.csi.k8s.io CSI driver. Create the following file sc-nfs.yaml and change 10.0.0.42 to the NFS server:

   apiVersion: storage.k8s.io/v1
   kind: StorageClass
   metadata:
     name: nfs-csi
   provisioner: nfs.csi.k8s.io
   parameters:
     server: 10.0.0.42
     share: /srv/nfs
   reclaimPolicy: Delete
   volumeBindingMode: Immediate
   mountOptions:
     - hard
     - nfsvers=4.1

Apply it on the MicroK8s cluster:

   microk8s kubectl apply -f - < sc-nfs.yaml

The final step is to create a new 5gb PersistentVolumeClaim using the nfs-csi storage class. This is as simple as specifying storageClassName as nfs-csi in the PVC definition within the file pvc-nfs.yaml:

   apiVersion: v1
   kind: PersistentVolumeClaim
   metadata:
     name: my-pvc
   spec:
     storageClassName: nfs-csi
     accessModes: [ReadWriteOnce]
     resources:
       requests:
         storage: 5Gi

Then create the PVC with:

   microk8s kubectl apply -f - < pvc-nfs.yaml

Check the PVC configuration:

   microk8s kubectl describe pvc my-pvc

References

• Microk8s Documentation | Use NFS for Persistent Volumes