Install Kubernetes on CentOS 7

Prerequisites

• Multiple Linux servers running CentOS 7 (1 Master Node, Multiple Worker Nodes)
• A user account on every system with sudo or root privileges
• The yum package manager, included by default
• Command-line/terminal window
• To use Kubernetes, you need to install a containerization engine. Please refer the below link.
• https://kubeadm.blogspot.com/2020/04/install-docker-on-centos-7.html

STEP 1 - Configure Kubernetes Repository

Kubernetes packages are not available from official CentOS 7 repositories. Add this repository on both master and worker node.

root# cat <<EOF > /etc/yum.repos.d/kubernetes.rep

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

STEP 2 - Install kubelet, kubeadm, and kubectl

These 3 basic packages are required to be able to use Kubernetes and to be installed on all nodes.

root# yum install -y kubelet kubeadm kubectl

root# systemctl enable kubelet

root# systemctl start kubelet

Note - Before deploying a cluster, make sure to set hostnames, configure the firewall, and kernel settings.

STEP 3 - Set Hostname on Nodes

Give unique hostnames to each of your nodes.

root# hostnamectl set-hostname master-node

root# hostnamectl set-hostname worker-node1

Make a host entry or DNS record to resolve the hostname for all nodes

root# vi /etc/hosts

Add the below entry:

192.168.1.100 master.practice.com master-node

192.168.1.200 node1.practice.com node1 worker-node1

STEP 4 - Configure Firewall

The nodes, containers, and pods need to be able to communicate across the cluster to perform their functions. Firewalld is enabled in CentOS by default on the front-end. Add the following ports by entering the listed commands.

On the Master Node:

root# firewall-cmd --permanent --add-port=6443/tcp

root# firewall-cmd --permanent --add-port=2379-2380/tcp

root# firewall-cmd --permanent --add-port=10250/tcp

root# firewall-cmd --permanent --add-port=10251/tcp

root# firewall-cmd --permanent --add-port=10252/tcp

root# firewall-cmd --permanent --add-port=10255/tcp

root# firewall-cmd –-reload

Verify you are getting success message for each command.

On each worker node:

root# firewall-cmd --permanent --add-port=10251/tcp

root# firewall-cmd --permanent --add-port=10255/tcp

root# firewall-cmd –-reload

STEP 5 - Update Iptables Settings

Set the net.bridge.bridge-nf-call-iptables to ‘1’ in your sysctl config file. This ensures that packets are properly processed by IP tables during filtering and port forwarding.

root# cat  < /etc/sysctl.d/master_node_name

net.bridge.bridge-nf-call-iptables = 1
EOF 

root# sysctl --system

STEP 6 - Disable SELinux

The containers need to access the host filesystem. SELinux needs to be set to permissive mode, which effectively disables its security functions.

root# setenforce 0

root# sed -i ‘s/^SELINUX=enforcing$/SELINUX=permissive/’ /etc/selinux/config

STEP 7 - Disable SWAP

we need to disable SWAP to enable the kubelet to work properly

root# sed -i '/swap/d' /etc/fstab

root# swapoff -a