Install kubernetes with kubeadm and enable swap

Kubernetes
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Kubeadm is a tool that helps you bootstrap a simple Kubernetes cluster and simplifies the deployment process. In this post I will use kubeadm to install swap enabled kubernetes.

Parts of the Kubernetes series

In all the previous tutorials we disabled the host swap because Kubernetes dose not allowed to use it. In Kubernetes 1.28 the Linux swap usage

192.168.1.41  kubernetes01 # master node

# hardware requirement
4 CPU
16G RAM

Enable cgroupV2

sudo dnf install -y grubby
sudo grubby \
  --update-kernel=ALL \
  --args="systemd.unified_cgroup_hierarchy=1"

cat << EOF >> /etc/systemd/system.conf
DefaultCPUAccounting=yes
DefaultIOAccounting=yes
DefaultIPAccounting=yes
DefaultBlockIOAccounting=yes
EOF

init 6

Configure date time and selinux

timedatectl set-timezone Europe/Budapest

dnf install -y vim net-tools chrony ntpstat
timedatectl set-ntp true
systemctl enable chronyd --now

systemctl stop firewalld
systemctl mask firewalld

setenforce 0
sed -i 's/=\(enforcing\|permissive\)/=disabled/g' /etc/sysconfig/selinux
sed -i 's/=\(enforcing\|permissive\)/=disabled/g' /etc/selinux/config

echo "net.ipv6.conf.all.disable_ipv6 = 1" >> /etc/sysctl.conf
echo "net.ipv6.conf.default.disable_ipv6 = 1" >> /etc/sysctl.conf
sysctl -p

echo "centos.mydomain.lan" > /etc/hostname
hostnamectl set-hostname centos.mydomain.lan

ifconfig | grep inet | grep -v inet6 | cut -d" " -f10 | sed "s|$|   `hostname -s` `hostname -f`|" >> /etc/hosts
sed -i "s|::1|#::1|" /etc/hosts

Install containerd

dnf install -y epel-release
dnf install -y device-mapper-persistent-data lvm2 iproute-tc
dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
dnf install -y containerd.io

## Configure containerd
sudo mkdir -p /etc/containerd
sudo containerd config default > /etc/containerd/config.toml

Configuration

To use the systemd cgroup driver in /etc/containerd/config.toml with runc, set

nano /etc/containerd/config.toml
...
          [plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
            SystemdCgroup = true

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

sudo modprobe overlay
sudo modprobe br_netfilter

cat <<EOF | sudo tee /etc/sysctl.d/99-kubernetes-cri.conf
net.bridge.bridge-nf-call-iptables  = 1
net.ipv4.ip_forward                 = 1
net.bridge.bridge-nf-call-ip6tables = 1
EOF

sysctl --system

As you can see we dose n ot siabled the swap:

# show swap is on
$ swapon --show
NAME      TYPE      SIZE USED PRIO
/dev/sda1 partition   2G   0B   -2

# check for type cgroup2
$ mount -l|grep cgroup
cgroup2 on /sys/fs/cgroup type cgroup2 (rw,nosuid,nodev,noexec,relatime,seclabel,nsdelegate)

# check for cpu controller
$ cat /sys/fs/cgroup/cgroup.subtree_control
cpu io memory pids

Install kubeadm

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

sudo dnf -y install kubelet kubeadm kubectl --disableexcludes=kubernetes

# Start containerd
systemctl enable --now containerd

echo "runtime-endpoint: unix:///run/containerd/containerd.sock" > /etc/crictl.yaml
crictl ps

Change runtime in kubeadm config:

# add the following flags to KUBELET_KUBEADM_ARGS variable
cat << EOF > /etc/sysconfig/kubelet
KUBELET_EXTRA_ARGS="--node-ip=192.168.1.41 --cgroup-driver=systemd --fail-swap-on=false"
EOF

sudo systemctl enable --now kubelet
sudo systemctl status kubelet

kubeadm config images pull

Init master

nano kubeadm-config.yaml
---
apiVersion: "kubeadm.k8s.io/v1beta3"
kind: InitConfiguration
localAPIEndpoint:
  # local ip and lort
  advertiseAddress: 192.168.100.10
  bindPort: 6443
nodeRegistration:
  criSocket: unix:///run/containerd/containerd.sock
  imagePullPolicy: IfNotPresent
  taints: null
  kubeletExtraArgs:
    runtime-cgroups: "/system.slice/containerd.service"
    rotate-server-certificates: "true"
---
apiVersion: kubeadm.k8s.io/v1beta3
kind: ClusterConfiguration
# loadbalancer ip and port
controlPlaneEndpoint: "192.168.100.10:6443"
networking:
  serviceSubnet: "10.96.0.0/12"
  podSubnet: "10.244.0.0/16"
---
apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration
enableServer: true
failSwapOn: false
cgroupDriver: "systemd"
featureGates:
  NodeSwap: true
memorySwap:
  swapBehavior: LimitedSwap
---
apiVersion: kubeadm.k8s.io/v1beta3
kind: JoinConfiguration
nodeRegistration:
  criSocket: unix:///run/containerd/containerd.sock
  imagePullPolicy: IfNotPresent
  taints: null
  kubeletExtraArgs:
    runtime-cgroups: "/system.slice/containerd.service"
    rotate-server-certificates: "true"

kubeadm init --config kubeadm-config.yaml

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


kubectl apply -f https://github.com/coreos/flannel/raw/master/Documentation/kube-flannel.yml

Join workers to cluster

kubeadm join 192.168.100.10:6443 --token XXXXXXXX \
    --discovery-token-ca-cert-hash sha256:XXXXXXXX

yum install -y https://harbottle.gitlab.io/harbottle-main/7/x86_64/harbottle-main-release.rpm
yum install -y kubectx helm