This following steps cover the steps required to create a Kubernetes Lab on VirtualBox VMs. The steps to install VirtualBox, detail steps on how to create the VirtualBox VM and Guest OS installation are not covered. The VM OS will use Ubuntu-server 18.04 LTS.
You may change the network or IP addresses as per your network plan.

• Install VirtualBox on PC/Mac
• Create host-only network on VirtualBox, for example: vboxnet0 use IPv4 network address 192.168.70.0 (GW address: 192.168.70.1) and subnet 24 (Netmask: 255.255.255.0)
• Create 3 VMs with 2 vCPU, 4096GB RAM each (for lower spec system, you can cut the spec to half), 100GB storage. These VMs will be named as:
  • master-node
  • worker01-node
  • worker02-node.
• Attach 2 network interfaces on every VM:
  • NIC #1 usses bridge adapter, will be used for external connectivity. In this instruction, it is assumed that the external network is using network adress: 192.168.0.0/24. Where master-node will have static IP 192.168.0.10, worker01 will use 192.168.0.11 and worker02 will use 192.168.0.12.

Note: You may opt to NAT and VirtualBox port forwarding feature to SSH to the VM.

• NIC #2 usses host-only vboxnet0, will be used for internal connectivity
• Attach the Ubuntu-server ISO to each VM

Reference: Setup VM

Boot the VM to Ubuntu-server ISO

• Opt to install the openssh-server at the installation screen
• Set the user name and password
• Set the hostname according to the VM designated usage, for example: master-node
• Do not add any additonal packages
• Let the rest to default

Proceed with Ubuntu-server OS installation.

Reference: Ubuntu installation

Once the installation is finished login to each VM console using the user name and password created earlier.

• Configure the hostname:

# sudo hostnamectl set-hostname <hostname>

For example

# sudo hostnamectl set-hostname master-node

Note: If you have setup the hostname during installation, you may skip the above step

• Configure static IP address

# vi /etc/netplan/01-netcfg.yaml

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s3:
      dhcp4: no
      addresses:
        - 192.168.0.10/24
      gateway4: 192.168.0.1
      nameservers:
          addresses: [8.8.8.8, 1.1.1.1]        
    enp0s8:
      dhcp4: no
      addresses:
        - 192.168.70.3/24
      gateway4: 192.168.70.1

Note:
Change the addresses as per your network plan.
enp0s3 is NIC #1 the interface toward the bridge adapter.
enp0s8 is NIC #2 the interface toward the host-only network vboxnet0.
The external network is 192.168.0.0/24 and the static IP for external communication for this VM is 192.168.0.10.
The internal network is 192.168.70.0/24 and the static IP for internal communication for this VM is 192.168.70.3.

Next, apply the static IP configuration

# sudo netplan apply

Ensure that there is only 1 default route on VM. If there is any additionaly default route, remove the wrong default route. For example:

# ip r
default via 192.168.0.1 dev enp0s3 proto static
default via 192.168.70.1 dev enp0s8 proto static <--- not needed, remove it
...
...

# sudo ip r delete default via 192.168.70.1 dev enp0s8 proto static

Add this following service to remove the duplicated default route after reboot.

# sudo cat <<EOF | sudo tee /etc/systemd/system/cleanup-double-route.service
[Unit]
Description=Custom script, remove double default route on Ubuntu

[Service]
User=root
ExecStart=/bin/bash -c "ip route delete default via 192.168.70.1 dev enp0s8 proto static"

[Install]
WantedBy=multi-user.target
EOF

Start and enable the service.

# sudo system4ctl daemon-reload
# sudo systemctl restart cleanup-double-route.service
# sudo systemctl enable cleanup-double-route.service

Next,

• Login to VM using its IP and credential to test if SSH connection work.
• Repeat the steps to all VM but change the hostname and the IP addresses.

Note:

If you have ansible installed, you can use the add-cleanup-double-route.yaml to create cleanup-double-route.service.

We will follow the steps in Installing kubeadm page from kubernetes.io documentation.

The installation consist of 3 parts which need to be run on all nodes, master and worker nodes.

• Iptables setup
• Install CRI/Container Runtime
  • This is to install Container Runtimes such as containerd, cri-o etc
• Installing kubeadm, kubelet and kubectl

Once you finished those 3 steps, the kubelet will restarting every few seconds, as it waits in a crashloop for kubeadm to tell it what to do. Next step will be to initiate cluster using kubeadm.

I have created a simple shell script to automate the steps, no validation check etc. See k8s_install_ubuntu_allnodes.sh.
This script uses containerd as container runtime.
To execute the script, copy the script to all nodes and execute using sudo:

# sudo sh k8s_install_ubuntu_allnodes.sh

We will follow instructions in Creating a cluster with kubeadm to intiate master node.

• Execute kubeadm init command on master node as root user and note down the "kubeadm join" command in the output file

# sudo kubeadm init --pod-network-cidr 10.211.0.0/16 --apiserver-advertise-address=192.168.70.3

Output:

[init] Using Kubernetes version: v1.23.3
...
...

Your Kubernetes control-plane has initialized successfully!

To start using your cluster, you need to run the following as a regular user:

  mkdir -p $HOME/.kube
  sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
  sudo chown $(id -u):$(id -g) $HOME/.kube/config

Alternatively, if you are the root user, you can run:

  export KUBECONFIG=/etc/kubernetes/admin.conf

You should now deploy a pod network to the cluster.
Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:
  https://kubernetes.io/docs/concepts/cluster-administration/addons/

Then you can join any number of worker nodes by running the following on each as root:

kubeadm join 192.168.70.3:6443 --token ul3z4n.znd6xxxxxxxxxxxx \
        --discovery-token-ca-cert-hash sha256:xxxxxxxxxd6fde0f1e27e5bbb3d873f316a7d065fb5fe57517xxxxxxxxxxxxxxx

Note
10.211.0.0/16 is the POD network CIDR. You can select whichever network address that fit your requirement.
192.168.70.3 is the IP address of master node running on host-only vboxnet0 network. This IP was set at post-installation step.

• Copy the config Kube directory/file.

# mkdir -p $HOME/.kube;   sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config;   sudo chown $(id -u):$(id -g) $HOME/.kube/config

• Install etcdctl-client package.

# sudo install etcd-client -y

• Next, install the Weave network CNI so that the created POD can use POD network.

# kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"

Note:

• You can opt to install different network CNI. See Cluster Networking for more details.
• At cluster-network page, I shared steps to install calico and multus CNI.
  • If you wish to install Calico CNI instead of weave CNI.
  • If you wish to install Multus CNI to enable multiple interface on the POD.

SSH to each worker node and run the join command:

# kubeadm join 192.168.70.3:6443 --token ul3z4n.znd6xxxxxxxxxxxx \
        --discovery-token-ca-cert-hash sha256:xxxxxxxxxd6fde0f1e27e5bbb3d873f316a7d065fb5fe57517xxxxxxxxxxxxxxx)

Note:
The join command was printed out at the kubeadm init output. If you missed or loss the session, you can ask kubeadm to reprint the join command by running this command on master node:

# kubeadm token create --print-join-command

Login to master node. Execute these following commands.

# kubectl get nodes

Expected output: all nodes are in Ready state

# kubectl get pod -n kube-sytem

Expected output: all kube-system pods are in Running state

Create a test pod, for example:

# kubectl run nginx --image=nginx
pod/nginx created

# kubectl get pod nginx
NAME    READY   STATUS    RESTARTS   AGE
nginx   1/1     Running   0          37s

Expected output: The test pod nginx is in Running state.