Installing kubeadm

Installing kubeadm - 图1 This page shows how to install the kubeadm toolbox. For information on how to create a cluster with kubeadm once you have performed this installation process, see the Creating a cluster with kubeadm page.

This installation guide is for Kubernetes v1.31. If you want to use a different Kubernetes version, please refer to the following pages instead:

Before you begin

  • A compatible Linux host. The Kubernetes project provides generic instructions for Linux distributions based on Debian and Red Hat, and those distributions without a package manager.
  • 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.

Note:

The kubeadm installation is done via binaries that use dynamic linking and assumes that your target system provides glibc. This is a reasonable assumption on many Linux distributions (including Debian, Ubuntu, Fedora, CentOS, etc.) but it is not always the case with custom and lightweight distributions which don’t include glibc by default, such as Alpine Linux. The expectation is that the distribution either includes glibc or a compatibility layer that provides the expected symbols.

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

These required ports need to be open in order for Kubernetes components to communicate with each other. You can use tools like netcat to check if a port is open. For example:

  1. nc 127.0.0.1 6443 -v

The pod network plugin you use 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.

Swap configuration

The default behavior of a kubelet is to fail to start if swap memory is detected on a node. This means that swap should either be disabled or tolerated by kubelet.

  • To tolerate swap, add failSwapOn: false to kubelet configuration or as a command line argument. Note: even if failSwapOn: false is provided, workloads wouldn’t have swap access by default. This can be changed by setting a swapBehavior, again in the kubelet configuration file. To use swap, set a swapBehavior other than the default NoSwap setting. See Swap memory management for more details.
  • To disable swap, sudo swapoff -a can be used to disable swapping temporarily. To make this change persistent across reboots, make sure swap is disabled in config files like /etc/fstab, systemd.swap, depending how it was configured on your system.

Installing a container runtime

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

By default, Kubernetes uses the Container Runtime Interface (CRI) to interface with your chosen container runtime.

If you don’t specify a runtime, kubeadm automatically tries to detect an installed container runtime by scanning through a list of known endpoints.

If multiple or no container runtimes are detected kubeadm will throw an error and will request that you specify which one you want to use.

See container runtimes for more information.

Note:

Docker Engine does not implement the CRI which is a requirement for a container runtime to work with Kubernetes. For that reason, an additional service cri-dockerd has to be installed. cri-dockerd is a project based on the legacy built-in Docker Engine support that was removed from the kubelet in version 1.24.

The tables below include the known endpoints for supported operating systems:

Linux container runtimes
RuntimePath to Unix domain socket
containerdunix:///var/run/containerd/containerd.sock
CRI-Ounix:///var/run/crio/crio.sock
Docker Engine (using cri-dockerd)unix:///var/run/cri-dockerd.sock
Windows container runtimes
RuntimePath to Windows named pipe
containerdnpipe:////./pipe/containerd-containerd
Docker Engine (using cri-dockerd)npipe:////./pipe/cri-dockerd

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, the kubelet 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:

Note: The legacy package repositories (apt.kubernetes.io and yum.kubernetes.io) have been deprecated and frozen starting from September 13, 2023. Using the new package repositories hosted at pkgs.k8s.io is strongly recommended and required in order to install Kubernetes versions released after September 13, 2023. The deprecated legacy repositories, and their contents, might be removed at any time in the future and without a further notice period. The new package repositories provide downloads for Kubernetes versions starting with v1.24.0.

Note:

There’s a dedicated package repository for each Kubernetes minor version. If you want to install a minor version other than v1.31, please see the installation guide for your desired minor version.

These instructions are for Kubernetes v1.31.

  1. Update the apt package index and install packages needed to use the Kubernetes apt repository:

    1. sudo apt-get update
    2. # apt-transport-https may be a dummy package; if so, you can skip that package
    3. sudo apt-get install -y apt-transport-https ca-certificates curl gpg

  2. Download the public signing key for the Kubernetes package repositories. The same signing key is used for all repositories so you can disregard the version in the URL:

    1. # If the directory `/etc/apt/keyrings` does not exist, it should be created before the curl command, read the note below.
    2. # sudo mkdir -p -m 755 /etc/apt/keyrings
    3. curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.31/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg

Note:

In releases older than Debian 12 and Ubuntu 22.04, directory /etc/apt/keyrings does not exist by default, and it should be created before the curl command.

  1. Add the appropriate Kubernetes apt repository. Please note that this repository have packages only for Kubernetes 1.31; for other Kubernetes minor versions, you need to change the Kubernetes minor version in the URL to match your desired minor version (you should also check that you are reading the documentation for the version of Kubernetes that you plan to install).

    1. # This overwrites any existing configuration in /etc/apt/sources.list.d/kubernetes.list
    2. echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.31/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list

  2. Update the apt package index, install kubelet, kubeadm and kubectl, and pin their version:

    1. sudo apt-get update
    2. sudo apt-get install -y kubelet kubeadm kubectl
    3. sudo apt-mark hold kubelet kubeadm kubectl

  3. (Optional) Enable the kubelet service before running kubeadm:

    1. sudo systemctl enable --now kubelet

  4. Set SELinux to permissive mode:

    These instructions are for Kubernetes 1.31.

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

Caution:

  • 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; for example, some cluster network plugins require that. You have to do this until SELinux support is improved in the kubelet.
  • You can leave SELinux enabled if you know how to configure it but it may require settings that are not supported by kubeadm.

  1. Add the Kubernetes yum repository. The exclude parameter in the repository definition ensures that the packages related to Kubernetes are not upgraded upon running yum update as there’s a special procedure that must be followed for upgrading Kubernetes. Please note that this repository have packages only for Kubernetes 1.31; for other Kubernetes minor versions, you need to change the Kubernetes minor version in the URL to match your desired minor version (you should also check that you are reading the documentation for the version of Kubernetes that you plan to install).

    1. # This overwrites any existing configuration in /etc/yum.repos.d/kubernetes.repo
    2. cat <<EOF | sudo tee /etc/yum.repos.d/kubernetes.repo
    3. [kubernetes]
    4. name=Kubernetes
    5. baseurl=https://pkgs.k8s.io/core:/stable:/v1.31/rpm/
    6. enabled=1
    7. gpgcheck=1
    8. gpgkey=https://pkgs.k8s.io/core:/stable:/v1.31/rpm/repodata/repomd.xml.key
    9. exclude=kubelet kubeadm kubectl cri-tools kubernetes-cni
    10. EOF

  2. Install kubelet, kubeadm and kubectl:

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

  3. (Optional) Enable the kubelet service before running kubeadm:

    1. sudo systemctl enable --now kubelet

Install CNI plugins (required for most pod network):

  1. CNI_PLUGINS_VERSION="v1.3.0"
  2. ARCH="amd64"
  3. DEST="/opt/cni/bin"
  4. sudo mkdir -p "$DEST"
  5. curl -L "https://github.com/containernetworking/plugins/releases/download/${CNI_PLUGINS_VERSION}/cni-plugins-linux-${ARCH}-${CNI_PLUGINS_VERSION}.tgz" | sudo tar -C "$DEST" -xz

Define the directory to download command files:

Note:

The DOWNLOAD_DIR variable must be set to a writable directory. If you are running Flatcar Container Linux, set DOWNLOAD_DIR="/opt/bin".

  1. DOWNLOAD_DIR="/usr/local/bin"
  2. sudo mkdir -p "$DOWNLOAD_DIR"

Optionally install crictl (required for interaction with the Container Runtime Interface (CRI), optional for kubeadm):

  1. CRICTL_VERSION="v1.31.0"
  2. ARCH="amd64"
  3. curl -L "https://github.com/kubernetes-sigs/cri-tools/releases/download/${CRICTL_VERSION}/crictl-${CRICTL_VERSION}-linux-${ARCH}.tar.gz" | sudo tar -C $DOWNLOAD_DIR -xz

Install kubeadm, kubelet and add a kubelet systemd service:

  1. RELEASE="$(curl -sSL https://dl.k8s.io/release/stable.txt)"
  2. ARCH="amd64"
  3. cd $DOWNLOAD_DIR
  4. sudo curl -L --remote-name-all https://dl.k8s.io/release/${RELEASE}/bin/linux/${ARCH}/{kubeadm,kubelet}
  5. sudo chmod +x {kubeadm,kubelet}
  7. RELEASE_VERSION="v0.16.2"
  8. curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/krel/templates/latest/kubelet/kubelet.service" | sed "s:/usr/bin:${DOWNLOAD_DIR}:g" | sudo tee /usr/lib/systemd/system/kubelet.service
  9. sudo mkdir -p /usr/lib/systemd/system/kubelet.service.d
  10. curl -sSL "https://raw.githubusercontent.com/kubernetes/release/${RELEASE_VERSION}/cmd/krel/templates/latest/kubeadm/10-kubeadm.conf" | sed "s:/usr/bin:${DOWNLOAD_DIR}:g" | sudo tee /usr/lib/systemd/system/kubelet.service.d/10-kubeadm.conf

Note:

Please refer to the note in the Before you begin section for Linux distributions that do not include glibc by default.

Install kubectl by following the instructions on Install Tools page.

Optionally, enable the kubelet service before running kubeadm:

  1. sudo systemctl enable --now kubelet

Note:

The Flatcar Container Linux distribution mounts the /usr directory as a read-only filesystem. Before bootstrapping your cluster, you need to take additional steps to configure a writable directory. See the Kubeadm Troubleshooting guide to learn how to set up a writable directory.

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

Configuring a cgroup driver

Both the container runtime and the kubelet have a property called “cgroup driver”, which is important for the management of cgroups on Linux machines.

Warning:

Matching the container runtime and kubelet cgroup drivers is required or otherwise the kubelet process will fail.

See Configuring a cgroup driver for more details.

Troubleshooting

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

What’s next