Installing kubeadm

This page shows how to install the kubeadm toolbox. For information how to create a cluster with kubeadm once you have performed this installation process, see the Using kubeadm to Create a Cluster page.

Before you begin

• One or more machines running one of:
  • Ubuntu 16.04+
  • Debian 9+
  • CentOS 7
  • Red Hat Enterprise Linux (RHEL) 7
  • Fedora 25+
  • HypriotOS v1.0.1+
  • Flatcar Container Linux (tested with 2512.3.0)
• 2 GB or more of RAM per machine (any less will leave little room for your apps)
• 2 CPUs or more
• Full network connectivity between all machines in the cluster (public or private network is fine)
• Unique hostname, MAC address, and product_uuid for every node. See here for more details.
• Certain ports are open on your machines. See here for more details.
• Swap disabled. You MUST disable swap in order for the kubelet to work properly.

Verify the MAC address and product_uuid are unique for every node

• You can get the MAC address of the network interfaces using the command ip link or ifconfig -a
• The product_uuid can be checked by using the command sudo cat /sys/class/dmi/id/product_uuid

It is very likely that hardware devices will have unique addresses, although some virtual machines may have identical values. 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.

Check network adapters

If you have more than one network adapter, and your Kubernetes components are not reachable on the default route, we recommend you add IP route(s) so Kubernetes cluster addresses go via the appropriate adapter.

Letting iptables see bridged traffic

Make sure that the br_netfilter module is loaded. This can be done by running lsmod | grep br_netfilter. To load it explicitly call sudo modprobe br_netfilter.

As a requirement for your Linux Node's iptables to correctly see bridged traffic, you should ensure net.bridge.bridge-nf-call-iptables is set to 1 in your sysctl config, e.g.

cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
sudo sysctl --system

For more details please see the Network Plugin Requirements page.

Check required ports

Control-plane node(s)

Worker node(s)

† Default port range for NodePort Services.

Any port numbers marked with * are overridable, so you will need to ensure any custom ports you provide are also open.

Although etcd ports are included in control-plane nodes, you can also host your own etcd cluster externally or on custom ports.

The pod network plugin you use (see below) may also require certain ports to be open. Since this differs with each pod network plugin, please see the documentation for the plugins about what port(s) those need.

Installing runtime

To run containers in Pods, Kubernetes uses a container runtime.

• Linux nodes
• other operating systems

Installing kubeadm, kubelet and kubectl

You will install these packages on all of your machines:

• kubeadm: the command to bootstrap the cluster.

• kubelet: the component that runs on all of the machines in your cluster and does things like starting pods and containers.

• kubectl: the command line util to talk to your cluster.

kubeadm will not install or manage kubelet or kubectl for you, so you will need to ensure they match the version of the Kubernetes control plane you want kubeadm to install for you. If you do not, there is a risk of a version skew occurring that can lead to unexpected, buggy behaviour. However, one minor version skew between the kubelet and the control plane is supported, but the kubelet version may never exceed the API server version. For example, kubelets running 1.7.0 should be fully compatible with a 1.8.0 API server, but not vice versa.

For information about installing kubectl, see Install and set up kubectl.

Warning: These instructions exclude all Kubernetes packages from any system upgrades. This is because kubeadm and Kubernetes require special attention to upgrade.

For more information on version skews, see:

• Kubernetes version and version-skew policy
• Kubeadm-specific version skew policy

• Ubuntu, Debian or HypriotOS
• CentOS, RHEL or Fedora
• Fedora CoreOS or Flatcar Container Linux

sudo apt-get update && sudo apt-get install -y apt-transport-https curl
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
cat <<EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list
deb https://apt.kubernetes.io/ kubernetes-xenial main
EOF
sudo apt-get update
sudo apt-get install -y kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl

cat <<EOF | sudo tee /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-\$basearch
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
exclude=kubelet kubeadm kubectl
EOF

# Set SELinux in permissive mode (effectively disabling it)
sudo setenforce 0
sudo sed -i 's/^SELINUX=enforcing$/SELINUX=permissive/' /etc/selinux/config

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

sudo systemctl enable --now kubelet

CNI_VERSION="v0.8.2"
sudo mkdir -p /opt/cni/bin
curl -L "https://github.com/containernetworking/plugins/releases/download/${CNI_VERSION}/cni-plugins-linux-amd64-${CNI_VERSION}.tgz" | sudo tar -C /opt/cni/bin -xz

DOWNLOAD_DIR=/usr/local/bin
sudo mkdir -p $DOWNLOAD_DIR

CRICTL_VERSION="v1.17.0"
curl -L "https://github.com/kubernetes-sigs/cri-tools/releases/download/${CRICTL_VERSION}/crictl-${CRICTL_VERSION}-linux-amd64.tar.gz" | sudo tar -C $DOWNLOAD_DIR -xz

RELEASE="$(curl -sSL https://dl.k8s.io/release/stable.txt)"
cd $DOWNLOAD_DIR
sudo curl -L --remote-name-all https://storage.googleapis.com/kubernetes-release/release/${RELEASE}/bin/linux/amd64/{kubeadm,kubelet,kubectl}
sudo chmod +x {kubeadm,kubelet,kubectl}

RELEASE_VERSION="v0.4.0"
curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/kubepkg/templates/latest/deb/kubelet/lib/systemd/system/kubelet.service" | sed "s:/usr/bin:${DOWNLOAD_DIR}:g" | sudo tee /etc/systemd/system/kubelet.service
sudo mkdir -p /etc/systemd/system/kubelet.service.d
curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/kubepkg/templates/latest/deb/kubeadm/10-kubeadm.conf" | sed "s:/usr/bin:${DOWNLOAD_DIR}:g" | sudo tee /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

systemctl enable --now kubelet

The kubelet is now restarting every few seconds, as it waits in a crashloop for kubeadm to tell it what to do.

Configure cgroup driver used by kubelet on control-plane node

When using Docker, kubeadm will automatically detect the cgroup driver for the kubelet and set it in the /var/lib/kubelet/config.yaml file during runtime.

If you are using a different CRI, you must pass your cgroupDriver value to kubeadm init, like so:

apiVersion: kubelet.config.k8s.io/v1beta1
kind: KubeletConfiguration
cgroupDriver: <value>

For further details, please read Using kubeadm init with a configuration file.

Please mind, that you only have to do that if the cgroup driver of your CRI is not cgroupfs, because that is the default value in the kubelet already.

Note: Since --cgroup-driver flag has been deprecated by kubelet, if you have that in /var/lib/kubelet/kubeadm-flags.env or /etc/default/kubelet(/etc/sysconfig/kubelet for RPMs), please remove it and use the KubeletConfiguration instead (stored in /var/lib/kubelet/config.yaml by default).

Restarting the kubelet is required:

systemctl daemon-reload
systemctl restart kubelet

The automatic detection of cgroup driver for other container runtimes like CRI-O and containerd is work in progress.

Troubleshooting

If you are running into difficulties with kubeadm, please consult our troubleshooting docs.

What's next

• Using kubeadm to Create a Cluster