Install k8s + flannel on debian / ubuntu for master / worker node

install-k8s-flannel-debian+ubuntu.bash

install_docker () {
    distro=$(cat /etc/*-release | grep DISTRIB_ID | awk -F '=' '{print $2}' | awk '{print tolower($0)}')
    distroList=("debian" "ubuntu")

    if [[ -n "${distro}" ]]; then
        if [[ " ${distroList[*]} " =~ " ${distro} " ]]; then
            echo "Installing kubernetes on $distro"
        else
            echo "Upsupported system distro: ${distro}"
            echo "<distro> must be one of: ${distroList[*]}"
            exit 1
        fi
    else
        echo "Unknown system distro"
        exit 1
    fi

    # Install docker
    sudo apt-get update
    sudo apt-get install -y \
        ca-certificates \
        curl \
        gnupg \
        lsb-release
    sudo mkdir -p /etc/apt/keyrings
    curl -fsSL https://download.docker.com/linux/${distro}/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
    echo \
      "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/${distro} \
      $(lsb_release -cs) stable" | sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
    sudo apt-get update
    sudo apt-get install -y docker-ce docker-ce-cli containerd.io docker-compose-plugin
}

install_kubernetes () {
    # Install kubernetes (kubeadm)
    sudo apt-get update
    sudo apt-get install -y apt-transport-https ca-certificates curl
    curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
    echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee -a /etc/apt/sources.list.d/kubernetes.list
    sudo apt-get update
    sudo apt-get install -y kubelet kubeadm kubectl
    sudo apt-mark hold kubelet kubeadm kubectl

    # Remove containerd config and restart
    sudo rm /etc/containerd/config.toml
    sudo systemctl restart containerd
}

setup_master () {
    # Initialize master node using kubeadm
    sudo kubeadm init --pod-network-cidr=10.244.0.0/16

    # Run kubernetes as a regular user
    sudo mkdir -p $HOME/.kube
    sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
    sudo chown $(id -u):$(id -g) $HOME/.kube/config

    # Apply flannel add-on
    sudo apt-get install -y wget
    wget https://github.com/flannel-io/flannel/releases/download/v0.18.1/flanneld-amd64
    sudo mkdir -p /opt/bin
    sudo mv flanneld-amd64 /opt/bin/flanneld
    kubectl apply -f https://raw.githubusercontent.com/flannel-io/flannel/master/Documentation/kube-flannel.yml

    # Print join information again
    kubeadm token create --print-join-command

    # Untaint master node to allow pod scheduling on master node
    # kubectl taint nodes --all node-role.kubernetes.io/master-
    # kubectl taint nodes --all node-role.kubernetes.io/control-plane-
}

setup_worker () {
    # Join master node
    echo "==================================================================================="
    echo "Joining master node by running the following command:"
    echo "-----------------------------------------------------------------------------------"
    echo "kubeadm join <master-ip>:6443 --token <token> --discovery-token-ca-cert-hash <hash>"
    echo "==================================================================================="
}

main () {
    variant=$1
    variantList=("master" "worker")

    if [[ -n "${variant}" ]]; then
        if [[ " ${variantList[*]} " =~ " ${variant} " ]]; then
            echo "Installing kubernetes for ${variant} node"
        else
            echo "Upsupported variant: ${variant}"
            echo "<variant> must be one of: ${variantList[*]}"
            exit 1
        fi
    else
        echo "Unknown variant"
        echo "Usage: $0 [master|worker]"
        exit 1
    fi
    
    # Swap can cause problem for `kubeadm init`
    # This works only temporarily. See the blow comments for a permanent solution.
    sudo swapoff -a
    
    install_docker
    install_kubernetes
    if [[ "${variant}" == "master" ]]; then
        setup_master
    else
        setup_worker
    fi
    
    echo "Done!"
}

main "$@"; exit

Usage:

bash install-k8s-flannel-debian+ubuntu.bash [master|worker]

Do not run this script with sudo since some commands should not be run as root.

Pitfalls:

1. Turn off the swap permanently. If you have swap on, you might have a problem with kubeadm init.
   • sudo swapoff -a can temporarily turn off your swap.
   • To turn it off permanently, comment out the line for swap in /etc/fstab and then restart. You can delete the swap file to free some space.
2. (2022-07-23) It is known that Kubernetes might not work on some newest Linux distributions such as Ubuntu >= 21 and Debian >= 11 (List not complete). It has something to do with the cgroup version. Check the issue for more details. Therefore, try to install them on an older OS version such as Ubuntu 20.04 or Debian 10.
   • (2022-09-26) UPDATE: The support for cgroup v2 has already been added to the stable release of kubernetes. If the error still happens, try to add this line.
3. Normally, you should set up a static internal IP for your master. If the internal IP of the master changed after the reboot, kubelet won't be able to start.

Useful Commands:

1. Restart kubelet: sudo systemctl restart kubelet;
2. Monitor the log of kubelet: sudo journalctl -u kubelet -n 100 -f;
3. Reset kubeadm if something goes wrong: sudo kubeadm reset. You may need to remove ~/.kube as well.