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Installing kubeadm templates/task 20

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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.

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  • One or more machines running one of:
    • Ubuntu 16.04+
    • Debian 9
    • CentOS 7
    • RHEL 7
    • Fedora 25/26 (best-effort)
    • HypriotOS v1.0.1+
    • Container Linux (tested with 1800.6.0)
  • 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.

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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.

Check required ports

Master node(s)

Protocol Direction Port Range Purpose Used By
TCP Inbound 6443* Kubernetes API server All
TCP Inbound 2379-2380 etcd server client API kube-apiserver, etcd
TCP Inbound 10250 Kubelet API Self, Control plane
TCP Inbound 10251 kube-scheduler Self
TCP Inbound 10252 kube-controller-manager Self

Worker node(s)

Protocol Direction Port Range Purpose Used By
TCP Inbound 10250 Kubelet API Self, Control plane
TCP Inbound 30000-32767 NodePort Services** All

** 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 master 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

Since v1.6.0, Kubernetes has enabled the use of CRI, Container Runtime Interface, by default. The container runtime used by default is Docker, which is enabled through the built-in dockershim CRI implementation inside of the kubelet.

Other CRI-based runtimes include:

Refer to the CRI installation instructions for more information.

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 panel 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.

{{< warning >}} These instructions exclude all Kubernetes packages from any system upgrades. This is because kubeadm and Kubernetes require special attention to upgrade. {{</ warning >}}

For more information on version skews, see:

{{< tabs name="k8s_install" >}} {{% tab name="Ubuntu, Debian or HypriotOS" %}}

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

{{% /tab %}} {{% tab name="CentOS, RHEL or Fedora" %}}

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
exclude=kube*
EOF

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

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

systemctl enable kubelet && systemctl start kubelet

Note:

  • Setting SELinux in permissive mode by running setenforce 0 and sed ... effectively disables it. This is required to allow containers to access the host filesystem, which is needed by pod networks for example. You have to do this until SELinux support is improved in the kubelet.

  • Some users on RHEL/CentOS 7 have reported issues with traffic being routed incorrectly due to iptables being bypassed. You should ensure net.bridge.bridge-nf-call-iptables is set to 1 in your sysctl config, e.g.

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

{{% /tab %}} {{% tab name="Container Linux" %}} Install CNI plugins (required for most pod network):

CNI_VERSION="v0.6.0"
mkdir -p /opt/cni/bin
curl -L "https://github.com/containernetworking/plugins/releases/download/${CNI_VERSION}/cni-plugins-amd64-${CNI_VERSION}.tgz" | tar -C /opt/cni/bin -xz

Install crictl (required for kubeadm / Kubelet Container Runtime Interface (CRI))

CRICTL_VERSION="v1.11.1"
mkdir -p /opt/bin
curl -L "https://github.com/kubernetes-incubator/cri-tools/releases/download/${CRICTL_VERSION}/crictl-${CRICTL_VERSION}-linux-amd64.tar.gz" | tar -C /opt/bin -xz

Install kubeadm, kubelet, kubectl and add a kubelet systemd service:

RELEASE="$(curl -sSL https://dl.k8s.io/release/stable.txt)"

mkdir -p /opt/bin
cd /opt/bin
curl -L --remote-name-all https://storage.googleapis.com/kubernetes-release/release/${RELEASE}/bin/linux/amd64/{kubeadm,kubelet,kubectl}
chmod +x {kubeadm,kubelet,kubectl}

curl -sSL "https://raw.githubusercontent.com/kubernetes/kubernetes/${RELEASE}/build/debs/kubelet.service" | sed "s:/usr/bin:/opt/bin:g" > /etc/systemd/system/kubelet.service
mkdir -p /etc/systemd/system/kubelet.service.d
curl -sSL "https://raw.githubusercontent.com/kubernetes/kubernetes/${RELEASE}/build/debs/10-kubeadm.conf" | sed "s:/usr/bin:/opt/bin:g" > /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

Enable and start kubelet:

systemctl enable kubelet && systemctl start kubelet

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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 Master Node

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

If you are using a different CRI, you have to modify the file /etc/default/kubelet with your cgroup-driver value, like so:

KUBELET_EXTRA_ARGS=--cgroup-driver=<value>

This file will be used by kubeadm init and kubeadm join to source extra user defined arguments for the kubelet.

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.

Restarting the kubelet is required:

systemctl daemon-reload
systemctl restart kubelet

Troubleshooting

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

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