Prerequisites

This document will demonstrate how to fulfill the prerequsites for kubeadm from scratch. It's meant for Linux (RHEL), but you might find similar options if you're using a different Linux distribution.

Minimum Requirements

• Linux

• At least 2GB RAM

free -h

• At least 2 CPU

lscpu | less

Configure node environment

Host configuration

Set up hostname as master1 (optional name)

sudo hostnamectl set-hostname master1

Verify Host details

hostnamectl

Retrieve host IP address

hostname -I

Append the ip and hostname into /etc/hosts file

sudo sh -c 'echo 192.168.xxx.xxx master1 >> /etc/hosts'

Network configuration

Enable IPVS modules

IPVS proxy mode

Install required package

sudo yum install -y ipvsadm conntrack-tools

Create a config file for loading modules automatically at boot time.

cat > /etc/modules-load.d/ipvs.conf <<EOF
ip_vs
ip_vs_rr
ip_vs_wrr
ip_vs_sh
nf_conntrack
EOF

Manually load the modules immediately

sudo modprobe ip_vs
sudo modprobe ip_vs_rr
sudo modprobe ip_vs_wrr
sudo modprobe ip_vs_sh
sudo modprobe nf_conntrack

Enable br_netfilter and overlay modules

Forwarding IPv4 and letting iptables see bridged traffic

Create a config file for loading modules automatically at boot time.

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

Manually load the modules immediately

sudo modprobe overlay
sudo 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

sudo sysctl --system

Verify that the br_netfilter, overlay modules are loaded at runtime

lsmod | grep br_netfilter
lsmod | grep overlay

Verify whether IPv4 forwarding and Bridged traffic are enabled by checking if the system variable is set to '1'

sysctl net.bridge.bridge-nf-call-iptables \
net.bridge.bridge-nf-call-ip6tables \
net.ipv4.ip_forward

Swap configuration

Swap configuration. The default behavior of a kubelet was to fail to start if swap memory was detected on a node. See Swap memory management for more details.

Verify the usage of Swap storage on your Linux server

free -h

Disable Swap

swapoff -a

De-activate Swap persistent across reboots

sudo sed -e '/swap/s/^/#/g' -i /etc/fstab

Verify whethe Swap is disabled by checking if the value is '0'

free -h

Install Docker Engine

Install the yum-utils package (which provides the yum-config-manager utility) and set up the repository.

Install using the rpm repository

sudo yum install -y yum-utils
sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

Install Docker Engine, containerd, and Docker Compose with latest version

sudo yum install -y docker-ce \
docker-ce-cli \
containerd.io \
docker-buildx-plugin \
docker-compose-plugin

Start and enable docker service

sudo systemctl start docker
sudo systemctl enable docker

Check Docker Status

sudo systemctl status docker

Set systemd as cgroupdriver

sudo tee /etc/docker/daemon.json > /dev/null << EOF
{
  "exec-opts": ["native.cgroupdriver=systemd"],
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "100m"
  },
  "storage-driver": "overlay2"
}
EOF

Reload daemon

sudo systemctl daemon-reload

Restart docker service

sudo systemctl restart docker

Container runtimes configuration

Since the default config.toml file contains only a partial configuration of containerd, we need to export the full list of settings for further overrides.

Backup the original containerd configuration file.

sudo mv /etc/containerd/config.toml /etc/containerd/config.toml.orig

Export the default setting of containerd configuration

sudo containerd config default | sudo tee /etc/containerd/config.toml > /dev/null

To configure the systemd as cgroup driver

The cgroupfs driver is not recommended when systemd is the init system because systemd expects a single cgroup manager on the system. cgroupfs driver Configuring the systemd cgroup driver

sudo sed -i '/SystemdCgroup/s/false/true/' /etc/containerd/config.toml

Update the version of sandbox (pause) image

Overriding the sandbox (pause) image https://kubernetes.io/docs/setup/production-environment/container-runtimes/#override-pause-image-containerd

sudo sed -i '/sandbox_image/s/3.6/3.9/' /etc/containerd/config.toml

Restart and enable containerd service

sudo systemctl restart containerd
sudo systemctl enable containerd

Completed