Three servers running CentOS 8 – 1 Master Node and 2 Worker Nodes.

It is recommended that your nodes should have at least 2 CPUs with 2GB RAM or more per machine. This is not a strict requirement but is largely driven by the needs of the application you intend to run.

Internet connectivity on all your nodes. We will be fetching Kubernetes and docker packages from the repository. Equally, you will need to make sure that the DNF package manager is installed by default and can fetch packages remotely.

All your nodes should also be able to connect to one another, either on a private or public network, whichever is available.

You will also need access to an account with sudo or root privileges. In this tutorial, I will be using my root account.

 Most nodes generally come with unique MAC addresses, however, in some unique cases, some Virtual Machines may have identical MAC addresses. It is therefore recommended that you confirm that the Product_UUID and the MAC address are not identical in any of the nodes. 

 Kubernetes uses these values to uniquely identify the nodes in the cluster. If these values are not unique to each node, the installation process may fail. 

 To check the MAC address of the network interface and compare it. 

 To check the product_uuid and compare, run the following command. 

Our installation is designed to have the Master-Node controlling the Worker Nodes. At the end of this installation, our logical architecture will look something like this.

Master Node – This machine generally acts as the control plane and runs the cluster database and the API server (which the kubectl CLI communicates with).

Installation of Kubernetes Cluster on Master-Node

For Kubernetes to work, you will need a containerization engine. As mentioned, we will be using Docker-CE.

The following institutions will be performed on CentOS 8 Master-Node.

Step 1: Prepare Hostname, Firewall, and SELinux

 On your CentOS 8 Master-Node, set the system hostname and update DNS in your /etc/hosts file. 

# hostnamectl set-hostname master-node
# cat <<EOF>> /etc/hosts
192.168.0.47 master-node
192.168.0.48 node-1 worker-node-1
192.168.0.49 node-2 worker-node-2
EOF

 Next, ping your worker-node-1 and worker-node-2 to check if your updated host file is working correctly using the ping command. 

 Next, disable Selinux, as this is required to allow containers to access the host filesystem, which is needed by pod networks and other services. 

 Setting setenforce to 0 effectively sets SELinux to permissive, which effectively disables SELinux until the next reboot. To completely disable it, use the below command and reboot. 

# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux
# reboot

 Kubernetes makes use of various ports for communication and access and these ports need to be accessible to Kubernetes and not limited by the firewall. 

 Configure the firewall rules on the ports. 

# firewall-cmd --permanent --add-port=6443/tcp
# firewall-cmd --permanent --add-port=2379-2380/tcp
# firewall-cmd --permanent --add-port=10250/tcp
# firewall-cmd --permanent --add-port=10251/tcp
# firewall-cmd --permanent --add-port=10252/tcp
# firewall-cmd --permanent --add-port=10255/tcp
# firewall-cmd --reload
# modprobe br_netfilter
# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

 You will need to add the Docker repository first as it is no longer in the default package list using the following dnf config-manager command. 

# dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo

 Also install containerd.io package which is available as a daemon that manages the complete container lifecycle of its host system, from image transfer and storage to container execution and supervision to low-level storage to network attachments and beyond. 

# dnf install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.6-3.3.el7.x86_64.rpm

 Now install the latest version of a docker-ce package. 

 You can now enable and start the docker service. 

# systemctl enable docker
# systemctl start docker

Step 3: Install Kubernetes (Kubeadm) on CentOS 8

 Next, you will need to add Kubernetes repositories manually as they do not come installed by default on CentOS 8. 

# cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOF

Kubeadm helps you bootstrap a minimum viable Kubernetes cluster that conforms to best practices. With kubeadm, your cluster should pass the Kubernetes Conformance tests.

Kubeadm also supports other cluster lifecycle functions, such as upgrades, downgrade, and managing bootstrap tokens. Kubeadm is also integration-friendly with other orchestration tools like Ansible and Terraform.

With the package repo now ready, you can go ahead and install kubeadm package.

  When the installation completes successfully, enable and start the service. 

# systemctl enable kubelet
# systemctl start kubelet

Step 4: Create a control-plane Master with kubeadm

The Kubernetes master which acts as the control plane for the cluster runs a few critical services necessary for the cluster. As such, the initialization process will do a series of prechecks to ensure that the machine is ready to run Kubernetes. These prechecks expose warnings and exit on errors. kubeadm init then downloads and installs the cluster control plane components.

Now it’s time to initialize Kubernetes master, but before that, you must disable swap in order to run “kubeadm init“ command.

 Initializing Kubernetes master is a completely automated process that is controlled by the “kubeadm init“ command as shown. 

 Next, copy the following command and store it somewhere, as we required to run this command on the worker nodes later. 

kubeadm join 192.168.0.47:6443 --token nu06lu.xrsux0ss0ixtnms5  \ --discovery-token-ca-cert-hash ha256:f996ea35r4353d342fdea2997a1cf8caeddafd6d4360d606dbc82314683478hjmf7

# kubeadm join 192.168.0.47:6443 --token nu06lu.xrsux0ss0ixtnms5 –discovery token-ca-cert-hash sha256:f996ea35r4353d342fdea2997a1cf8caeddafd6d4360d606dbc82314683478hjmf7

In this blog, we will go through the process of installing the Kubernetes cluster on the CentOS 8 platform with Docker-CE.

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