Overview

As a container orchestration, Kubernetes help anyone who needs to deploy a container service in a declarative way. Kubernetes will manage and maintain every resource to meet the state needed by the developer. Developer simply defined the desired state by JSON or YAML file and sends it to Kubernetes API. In this article, I will guide you to deploy a Kubernetes cluster with CRI-O as container runtime on RHEL-based OS, Rocky Linux 9.1.

Installation

Pre-requisites

We need 1 node for the control-plane node and at least 1 node or more nodes for the worker node with the specifications:

Control-plane node:
- 2 core or more processor
- 2 GB or more memory
- Rocky Linux 9
Worker node:
- 4 core or more processor
- 8 GB or more memory
- Rocky Linux 9

Steps

Master Node

Configure firewall on every node

You need to set firewall rules on the node(s) to open several inbound ports or connections between the Kubernetes cluster node based on Kubernetes Documentation.

 firewall-cmd --permanent --new-zone=kubernetes-master
 firewall-cmd --permanent --zone=kubernetes-master --add-service=ssh
 firewall-cmd --permanent --zone=kubernetes-master --add-port={6443,2379,2380,10250,10259,10257}/tcp
 firewall-cmd --reload
 firewall-cmd --permanent --zone=kubernetes-master --change-interface=enp1s0
 firewall-cmd --set-default-zone=kubernetes-master

Setup CRI-O

CRI-O repository will be added to YUM depending Kubernetes version want to be installed by specifying the VERSION environment variable.

 export VERSION=1.26
 export OS=CentOS_8_Stream
 curl -L -o /etc/yum.repos.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable:/cri-o:/$VERSION/$OS/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo
 yum install cri-o -y
 systemctl enable --now crio

Setup kubeadm, kubelet, and kubectl

Kubernetes’ repository will be added to YUM and install kubelet, kubectl and kubeadm following the version of Kubernetes want to installed. See Kubernetes Releases.

 cat <<EOF | sudo tee /etc/yum.repos.d/kubernetes.repo
 [kubernetes]
 name=Kubernetes
 baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\$basearch
 enabled=1
 gpgcheck=1
 gpgkey=https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
 exclude=kubelet kubeadm kubectl
 EOF
 # Set SELinux in permissive mode (effectively disabling it)
 sudo setenforce 0
 sudo sed -i 's/^SELINUX=enforcing$/SELINUX=permissive/' /etc/selinux/config
 yum install kubelet-1.26.5 kubectl-1.26.5 kubeadm-1.26.5 --disableexcludes=kubernetes

Configure prerequisites

 cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf
 overlay
 br_netfilter
 EOF

 modprobe overlay
 modprobe br_netfilter

 # sysctl params required by setup, params persist across reboots
 cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
 net.bridge.bridge-nf-call-iptables  = 1
 net.bridge.bridge-nf-call-ip6tables = 1
 net.ipv4.ip_forward                 = 1
 EOF

 # Apply sysctl params without reboot
 sysctl --system

Create kubeadm’s and InitConfiguration and ClusterConfiguration file for master node

 vim kubeadm-worker-conf.yaml

 apiVersion: kubeadm.k8s.io/v1beta3
 kind: InitConfiguration
 nodeRegistration:
  name: "master-node0"
  criSocket: "/var/run/crio/crio.sock"
 ---
 apiVersion: kubeadm.k8s.io/v1beta3
 kind: ClusterConfiguration
 networking:
  serviceSubnet: "10.10.0.0/16"
  podSubnet: "10.10.10.0/24"
  dnsDomain: "jesaya.lab"
 kubernetesVersion: "v1.26.5"
 controlPlaneEndpoint: "[control-plane-ip]:6443"
 clusterName: "[cluster-name]"

Initialize Kubeadm

 systemctl enable kubelet.service
 kubeadm init --config kubeadm-cluster-conf.yaml

Check the Kubernetes has been initilized

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

Worker node(s)