Install kubernetes (1.28) on Ubuntu Server 20.04 LTS

install_kubernetes.md

Install kubernetes (1.28) on Ubuntu Server 20.04 LTS

Tags: kubernetes, Ubuntu Server, containerd, Calico, virtualization Date: September 12, 2023

Minimum requirements for practice.

⚠️ It is highly recommended to assign fixed IPs to the machines.

Server	Hostname	Minimum requirements
Master	k8s-master	4GB Ram, 2vcpus
Worker	k8s-worker	4GB Ram, 2vcpus

1. Assembly and update of machines

We need to prepare the virtual machines in our favorite hypervisor (virtualbox, vmware, hyper-v, parallels...).

With the machines ready, we update the operating system:

sudo apt update && sudo apt -y full-upgrade [ -f /var/run/reboot-required ] && sudo reboot -f

2. Installation of kubelet, kubeadm and kubectl

When the servers are updated and restarted, we install the kubernetes repositories:

sudo apt -y install curl apt-transport-https

curl -fsSL https://packages.cloud.google.com/apt/doc/apt-key.gpg|sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/kubernetes.gpg

echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list

We install the packages and mark the kubernetes packages as hold. This will allow us to keep them in the current version even if we upgrade the machine, ensuring stability:

sudo apt update
sudo apt -y install wget kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl

We can confirm the installed packages and versions with the following command:

kubectl version --client && kubeadm version

3. Disable SWAP memory and activate kernel features.

Disable swap memory by commenting out the /etc/fstab file. You can edit it manually or use the following command to do it automatically:

sudo sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab

This is how it looks when the line commented:

/dev/disk/by-uuid/65504f19-362f-4fb6-a983-26d3541d5dc7 /boot ext4 defaults 0 1
#/swap.img      none    swap    sw      0       0

On the other hand, we use the following commands to activate the necessary features:

# Enable kernel modules
sudo modprobe overlay
sudo modprobe br_netfilter

# Add some settings to sysctl
sudo tee /etc/sysctl.d/kubernetes.conf<<EOF
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1
EOF

# Reload sysctl
sudo sysctl --system

4. Install containerd

You could also use docker or CRI-O, but personally I usually use containerd.

We can do this by launching the following commands:

# Configure persistent loading of modules
sudo tee /etc/modules-load.d/containerd.conf <<EOF
overlay
br_netfilter
EOF

# Install required packages
sudo apt install -y curl gnupg2 software-properties-common apt-transport-https ca-certificates

# Add Docker repo
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/docker-archive-keyring.gpg

sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

# Install containerd
sudo apt update
sudo apt install -y containerd.io

# Configure containerd and start service
sudo mkdir -p /etc/containerd
sudo containerd config default|sudo tee /etc/containerd/config.toml

# restart containerd
sudo systemctl restart containerd
sudo systemctl enable containerd
systemctl status  containerd

5. Install the master node

We download the images that Kubernetes needs to function. If we skip this step, it will be done automatically during the init process. Personally, I like to do it separately to verify that the container engine is working correctly.

sudo kubeadm config images pull

We modify the file /etc/hosts to associate the name we want to give to the master node with the machine's IP. In my case, I usually name it k8scp so we configure the node with a domain name to facilitate the process with the workers. File /etc/hosts:

127.0.0.1 localhost 
IP_OF_THE_MACHINE k8scp

Start the cluster with kubeadm init:

sudo kubeadm init --pod-network-cidr=172.24.0.0/16 --cri-socket=unix:///run/containerd/containerd.sock --upload-certs --control-plane-endpoint=k8scp

Once started, we can copy the configuration file to our base user (avoid using root):

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

Si por casualidad no os lo cogiera automáticamente, podríais modificar la variable de entorno donde se define la ruta del fichero config:

export KUBECONFIG=$HOME/.kube/config

Comprobar que el cluster funciona correctamente:

kubectl cluster-info

6. Installing the network plugin on the master node.

By default, Kubernetes requires a network manager (CNI) that will create a network to connect all pods together. It is essential for the node to function properly.

There are several alternatives, such as Flannel or Calico. This guide explains the installation of Calico (nothing to do with Cálico Electrónico).

The installation is done through Kubernetes objects declared in .yaml files. We can download the latest version from the project's releases page. As of now, I am downloading the latest version:

curl -O https://raw.githubusercontent.com/projectcalico/calico/v3.26.1/manifests/tigera-operator.yaml
curl -O https://raw.githubusercontent.com/projectcalico/calico/v3.26.1/manifests/custom-resources.yaml

Install the operator:

kubectl create -f tigera-operator.yaml

We would have the file custom-resources.yaml, which would need to be modified with the network range defined in the kubeadm init command. In the case of this guide, it is 172.24.0.0. We can do it with the following command:

sed -ie 's/192.168.0.0/172.24.0.0/g' custom-resources.yaml

We load the file that we have modified:

kubectl create -f custom-resources.yaml

And finally, we wait for all pods to be in the ready state:

kubectl get pods --all-namespaces -w

⚠️ Good practice dictates that the master node does not run pods (excluding those of the system itself), as this improves the stability of the cluster. If for some reason, or simply in a testing environment, you can disable this restriction with the following commands:

kubectl taint nodes --all node-role.kubernetes.io/control-plane-

We can confirm that the node is up and running:

kubectl get nodes -o wide

Extra 1. Command autocomplete in bash

Add bash autocomplete for cli.

echo 'source <(kubectl completion bash)' >>~/.bashrc

# Reload sourcefile again (located on home)
source .bashrc 

7. Add workers

⚠️ You must to repeat the steps 1-4 (included) to prepare the virtual machine to install kubernetes.

To join a worker on the cluster, we going to use this command:

kubeadm join \
<control-plane-host>:<control-plane-port> \
--token <token> \
--discovery-token-ca-cert-hash sha256:<hash>

The data that you need:

• Control plane host and port, in this case: k8scp:6443
• Token, launch this command on master server:

kubeadm token create

• Discovery token ca, lauch this command on master server again:

openssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex | sed 's/^.* //'

💡 If you want to see the active tokens: `kubeadm token list`

Now, use the completed kubeadm join command. If the process It's correct, you could se the node ready using kubectl get nodes on master API.

You could add all the workers that you want.

That´s all, see you in the next!