---
reviewers:
- sig-cluster-lifecycle
title: Creating a single master cluster with kubeadm
content_template: templates/task
---

{{% capture overview %}}

<img src="https://raw.githubusercontent.com/cncf/artwork/master/kubernetes/certified-kubernetes/versionless/color/certified-kubernetes-color.png" align="right" width="150px">**kubeadm** helps you bootstrap a minimum viable Kubernetes cluster that conforms to best practices.  With kubeadm, your cluster should pass [Kubernetes Conformance tests](https://kubernetes.io/blog/2017/10/software-conformance-certification). Kubeadm also supports other cluster 
lifecycle functions, such as upgrades, downgrade, and managing [bootstrap tokens](/docs/admin/bootstrap-tokens/). 

Because you can install kubeadm on various types of machine (e.g. laptop, server, 
Raspberry Pi, etc.), it's well suited for integration with provisioning systems 
such as Terraform or Ansible.

kubeadm's simplicity means it can serve a wide range of use cases:

- New users can start with kubeadm to try Kubernetes out for the first time.
- Users familiar with Kubernetes can spin up clusters with kubeadm and test their applications.
- Larger projects can include kubeadm as a building block in a more complex system that can also include other installer tools.

kubeadm's overall feature state is **Beta**. 

{{% /capture %}}

{{% capture prerequisites %}}

- One or more machines running a deb/rpm-compatible OS, for example Ubuntu or CentOS
- 2 GB or more of RAM per machine. Any less leaves little room for your
   apps.
- 2 CPUs or more on the master
- Full network connectivity among all machines in the cluster. A public or
   private network is fine.
 
{{% /capture %}}

{{% capture steps %}}

## Objectives

* Install a single master Kubernetes cluster or [high availability cluster](https://kubernetes.io/docs/setup/independent/high-availability/)
* Install a Pod network on the cluster so that your Pods can
  talk to each other

## Instructions

### Installing kubeadm on your hosts

See ["Installing kubeadm"](/docs/setup/independent/install-kubeadm/).

{{< note >}}
**Note:** If you have already installed kubeadm, run `apt-get update &&
apt-get upgrade` or `yum update` to get the latest version of kubeadm.

When you upgrade, the kubelet restarts every few seconds as it waits in a crashloop for
kubeadm to tell it what to do. This crashloop is expected and normal. 
After you initialize your master, the kubelet runs normally.
{{< /note >}}

### Initializing your master

The master is the machine where the control plane components run, including
etcd (the cluster database) and the API server (which the kubectl CLI
communicates with).

1. Choose a pod network add-on, and verify whether it requires any arguments to 
be passed to kubeadm initialization. Depending on which
third-party provider you choose, you might need to set the `--pod-network-cidr` to
a provider-specific value. See [Installing a pod network add-on](#pod-network).
1. (Optional) Unless otherwise specified, kubeadm uses the network interface associated 
with the default gateway to advertise the master's IP. To use a different 
network interface, specify the `--apiserver-advertise-address=<ip-address>` argument 
to `kubeadm init`. To deploy an IPv6 Kubernetes cluster using IPv6 addressing, you 
must specify an IPv6 address, for example `--apiserver-advertise-address=fd00::101`

Now run:

```bash
kubeadm init <args> 
```

### More information

For more information about `kubeadm init` arguments, see the [kubeadm reference guide](/docs/reference/setup-tools/kubeadm/kubeadm/).

For a complete list of configuration options, see the [configuration file documentation](/docs/reference/setup-tools/kubeadm/kubeadm-init/#config-file).

To customize control plane components, including optional IPv6 assignment to liveness probe for control plane components and etcd server, provide extra arguments to each component as documented in [custom arguments](/docs/admin/kubeadm#custom-args).

To run `kubeadm init` again, you must first [tear down the cluster](#tear-down).

If you join a node with a different architecture to your cluster, create a separate
Deployment or DaemonSet for `kube-proxy` and `kube-dns` on the node. This is because the Docker images for these
components do not currently support multi-architecture.

`kubeadm init` first runs a series of prechecks to ensure that the machine
is ready to run Kubernetes. These prechecks expose warnings and exit on errors. `kubeadm init`
then downloads and installs the cluster control plane components. This may take several minutes. 
The output should look like:

```
[init] Using Kubernetes version: vX.Y.Z
[preflight] Running pre-flight checks

... (log output of initialization workflow) ...

Your Kubernetes master has initialized successfully!

To start using your cluster, you need to run (as a regular user):

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

You should now deploy a pod network to the cluster.
Run "kubectl apply -f [podnetwork].yaml" with one of the addon options listed at:
  http://kubernetes.io/docs/admin/addons/

You can now join any number of machines by running the following on each node
as root:

  kubeadm join --token <token> <master-ip>:<master-port> --discovery-token-ca-cert-hash sha256:<hash>
```

To make kubectl work for your non-root user, run these commands, which are
also part of the `kubeadm init` output:

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

Alternatively, if you are the `root` user, you can run:

```bash
export KUBECONFIG=/etc/kubernetes/admin.conf
```

Make a record of the `kubeadm join` command that `kubeadm init` outputs. You
need this command to [join nodes to your cluster](#join-nodes).

The token is used for mutual authentication between the master and the joining
nodes.  The token included here is secret. Keep it safe, because anyone with this
token can add authenticated nodes to your cluster. These tokens can be listed,
created, and deleted with the `kubeadm token` command. See the
[kubeadm reference guide](/docs/reference/setup-tools/kubeadm/kubeadm-token/).

### Installing a pod network add-on {#pod-network}

{{< caution >}}
**Caution:** This section contains important information about installation and deployment order. Read it carefully before proceeding.
{{< /caution >}}

You must install a pod network add-on so that your pods can communicate with
each other.

The network must be deployed before any applications. An
internal helper service, kube-dns, will not start up before a network is installed. kubeadm
supports only Container Network Interface (CNI) based networks. It does not support kubenet.

Several projects provide Kubernetes pod networks using CNI, some of which also
support [Network Policy](/docs/concepts/services-networking/networkpolicies/). See the [add-ons page](/docs/concepts/cluster-administration/addons/) for a complete list of available network add-ons. 
- IPv6 support was added in [CNI v0.6.0](https://github.com/containernetworking/cni/releases/tag/v0.6.0). 
- [CNI bridge](https://github.com/containernetworking/plugins/blob/master/plugins/main/bridge/README.md) and [local-ipam](https://github.com/containernetworking/plugins/blob/master/plugins/ipam/host-local/README.md) are the only supported IPv6 network plugins in Kubernetes version 1.9.

Note that kubeadm sets up a more secure cluster by default and enforces use of [RBAC](/docs/reference/access-authn-authz/rbac/).
Make sure that your network manifest supports RBAC.

You can install a pod network add-on with the following command:

```bash
kubectl apply -f <add-on.yaml>
```

You can install only one pod network per cluster.

{{< tabs name="tabs-pod-install" >}}
{{% tab name="Choose one..." %}}
Please select one of the tabs to see installation instructions for the respective third-party Pod Network Provider.
{{% /tab %}}

{{% tab name="Calico" %}}
For more information about using Calico, see [Quickstart for Calico on Kubernetes](https://docs.projectcalico.org/latest/getting-started/kubernetes/), [Installing Calico for policy and networking](https://docs.projectcalico.org/latest/getting-started/kubernetes/installation/calico), and other related resources.

In order for Network Policy to work correctly, you need to pass `--pod-network-cidr=192.168.0.0/16` to `kubeadm init`. Note that Calico works on `amd64` only.

```shell
kubectl apply -f https://docs.projectcalico.org/v3.1/getting-started/kubernetes/installation/hosted/rbac-kdd.yaml
kubectl apply -f https://docs.projectcalico.org/v3.1/getting-started/kubernetes/installation/hosted/kubernetes-datastore/calico-networking/1.7/calico.yaml
```

{{% /tab %}}
{{% tab name="Canal" %}}
Canal uses Calico for policy and Flannel for networking. Refer to the Calico documentation for the [official getting started guide](https://docs.projectcalico.org/latest/getting-started/kubernetes/installation/flannel).

For Canal to work correctly, `--pod-network-cidr=10.244.0.0/16` has to be passed to `kubeadm init`. Note that Canal works on `amd64` only.

```shell
kubectl apply -f https://docs.projectcalico.org/v3.1/getting-started/kubernetes/installation/hosted/canal/rbac.yaml
kubectl apply -f https://docs.projectcalico.org/v3.1/getting-started/kubernetes/installation/hosted/canal/canal.yaml
```

{{% /tab %}}
{{% tab name="Flannel" %}}

For `flannel` to work correctly, `--pod-network-cidr=10.244.0.0/16` has to be passed to `kubeadm init`. Note that `flannel` works on `amd64`, `arm`, `arm64` and `ppc64le`. For it to work on a platform other than
`amd64`, you must manually download the manifest and replace `amd64` occurrences with your chosen platform.

Set `/proc/sys/net/bridge/bridge-nf-call-iptables` to `1` by running `sysctl net.bridge.bridge-nf-call-iptables=1`
to pass bridged IPv4 traffic to iptables' chains. This is a requirement for some CNI plugins to work, for more information
please see [here](https://kubernetes.io/docs/concepts/cluster-administration/network-plugins/#network-plugin-requirements).

```shell
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/v0.10.0/Documentation/kube-flannel.yml
```

For more information about `flannel`, see [the CoreOS flannel repository on GitHub
](https://github.com/coreos/flannel).
{{% /tab %}}

{{% tab name="Kube-router" %}}
Set `/proc/sys/net/bridge/bridge-nf-call-iptables` to `1` by running `sysctl net.bridge.bridge-nf-call-iptables=1`
to pass bridged IPv4 traffic to iptables' chains. This is a requirement for some CNI plugins to work, for more information
please see [here](https://kubernetes.io/docs/concepts/cluster-administration/network-plugins/#network-plugin-requirements).

Kube-router relies on kube-controller-manager to allocate pod CIDR for the nodes. Therefore, use `kubeadm init` with the `--pod-network-cidr` flag.

Kube-router provides pod networking, network policy, and high-performing IP Virtual Server(IPVS)/Linux Virtual Server(LVS) based service proxy.

For information on setting up Kubernetes cluster with Kube-router using kubeadm, please see official [setup guide](https://github.com/cloudnativelabs/kube-router/blob/master/docs/kubeadm.md).
{{% /tab %}}

{{% tab name="Romana" %}}
Set `/proc/sys/net/bridge/bridge-nf-call-iptables` to `1` by running `sysctl net.bridge.bridge-nf-call-iptables=1`
to pass bridged IPv4 traffic to iptables' chains. This is a requirement for some CNI plugins to work, for more information
please see [here](https://kubernetes.io/docs/concepts/cluster-administration/network-plugins/#network-plugin-requirements).

The official Romana set-up guide is [here](https://github.com/romana/romana/tree/master/containerize#using-kubeadm).

Romana works on `amd64` only.

```shell
kubectl apply -f https://raw.githubusercontent.com/romana/romana/master/containerize/specs/romana-kubeadm.yml
```
{{% /tab %}}

{{% tab name="Weave Net" %}}
Set `/proc/sys/net/bridge/bridge-nf-call-iptables` to `1` by running `sysctl net.bridge.bridge-nf-call-iptables=1`
to pass bridged IPv4 traffic to iptables' chains. This is a requirement for some CNI plugins to work, for more information
please see [here](https://kubernetes.io/docs/concepts/cluster-administration/network-plugins/#network-plugin-requirements).

The official Weave Net set-up guide is [here](https://www.weave.works/docs/net/latest/kube-addon/).

Weave Net works on `amd64`, `arm`, `arm64` and `ppc64le` without any extra action required.
Weave Net sets hairpin mode by default. This allows Pods to access themselves via their Service IP address
if they don't know their PodIP.

```shell
kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"
```
{{% /tab %}}
{{< /tabs >}}

Once you install a pod network, you can confirm that it works by
checking that the kube-dns pod is Running in the output of `kubectl get pods --all-namespaces`.
Once the kube-dns pod is up and running, you can continue by joining your nodes.

If your network is not working or kube-dns is not in the Running state, check
out our [troubleshooting docs](/docs/setup/independent/troubleshooting-kubeadm/).

### Master Isolation

By default, your cluster will not schedule pods on the master for security
reasons. If you want to be able to schedule pods on the master, e.g. for a
single-machine Kubernetes cluster for development, run:

```bash
kubectl taint nodes --all node-role.kubernetes.io/master-
```

With output looking something like:

```
node "test-01" untainted
taint key="dedicated" and effect="" not found.
taint key="dedicated" and effect="" not found.
```

This will remove the `node-role.kubernetes.io/master` taint from any nodes that
have it, including the master node, meaning that the scheduler will then be able
to schedule pods everywhere.

### Joining your nodes {#join-nodes}

The nodes are where your workloads (containers and pods, etc) run. To add new nodes to your cluster do the following for each machine:

* SSH to the machine
* Become root (e.g. `sudo su -`)
* Run the command that was output by `kubeadm init`. For example:

``` bash
kubeadm join --token <token> <master-ip>:<master-port> --discovery-token-ca-cert-hash sha256:<hash>
```

{{< note >}}
**Note:** To specify an IPv6 tuple for `<master-ip>:<master-port>`, IPv6 address must be enclosed in square brackets, for example: `[fd00::101]:2073`.
{{< /note >}}

The output should look something like:

```
[preflight] Running pre-flight checks

... (log output of join workflow) ...

Node join complete:
* Certificate signing request sent to master and response
  received.
* Kubelet informed of new secure connection details.

Run 'kubectl get nodes' on the master to see this machine join.
```

A few seconds later, you should notice this node in the output from `kubectl get
nodes` when run on the master.

### (Optional) Controlling your cluster from machines other than the master

In order to get a kubectl on some other computer (e.g. laptop) to talk to your
cluster, you need to copy the administrator kubeconfig file from your master
to your workstation like this:

``` bash
scp root@<master ip>:/etc/kubernetes/admin.conf .
kubectl --kubeconfig ./admin.conf get nodes
```

{{< note >}}
**Note:** The example above assumes SSH access is enabled for root. If that is not the
case, you can copy the `admin.conf` file to be accessible by some other user
and `scp` using that other user instead.

The `admin.conf` file gives the user _superuser_ privileges over the cluster.
This file should be used sparingly. For normal users, it's recommended to
generate an unique credential to which you whitelist privileges. You can do
this with the `kubeadm alpha phase kubeconfig user --client-name <CN>`
command. That command will print out a KubeConfig file to STDOUT which you
should save to a file and distribute to your user. After that, whitelist
privileges by using `kubectl create (cluster)rolebinding`.
{{< /note >}}

### (Optional) Proxying API Server to localhost

If you want to connect to the API Server from outside the cluster you can use
`kubectl proxy`:

```bash
scp root@<master ip>:/etc/kubernetes/admin.conf .
kubectl --kubeconfig ./admin.conf proxy
```

You can now access the API Server locally at `http://localhost:8001/api/v1`

## Tear down {#tear-down}

To undo what kubeadm did, you should first [drain the
node](/docs/reference/generated/kubectl/kubectl-commands#drain) and make
sure that the node is empty before shutting it down.

Talking to the master with the appropriate credentials, run:

```bash
kubectl drain <node name> --delete-local-data --force --ignore-daemonsets
kubectl delete node <node name>
```

Then, on the node being removed, reset all kubeadm installed state:

```bash
kubeadm reset
```

If you wish to start over simply run `kubeadm init` or `kubeadm join` with the
appropriate arguments.

More options and information about the
[`kubeadm reset command`](/docs/reference/setup-tools/kubeadm/kubeadm-reset/).

## Maintaining a cluster {#lifecycle}

Instructions for maintaining kubeadm clusters (e.g. upgrades,downgrades, etc.) can be found [here.](/docs/tasks/administer-cluster/kubeadm)

## Explore other add-ons {#other-addons}

See the [list of add-ons](/docs/concepts/cluster-administration/addons/) to explore other add-ons,
including tools for logging, monitoring, network policy, visualization &amp;
control of your Kubernetes cluster.

## What's next {#whats-next}

* Verify that your cluster is running properly with [Sonobuoy](https://github.com/heptio/sonobuoy)
* Learn about kubeadm's advanced usage in the [kubeadm reference documentation](/docs/reference/setup-tools/kubeadm/kubeadm)
* Learn more about Kubernetes [concepts](/docs/concepts/) and [`kubectl`](/docs/user-guide/kubectl-overview/).
* Configure log rotation. You can use **logrotate** for that. When using Docker, you can specify log rotation options for Docker daemon, for example `--log-driver=json-file --log-opt=max-size=10m --log-opt=max-file=5`. See [Configure and troubleshoot the Docker daemon](https://docs.docker.com/engine/admin/) for more details.

## Feedback {#feedback}

* For bugs, visit [kubeadm Github issue tracker](https://github.com/kubernetes/kubeadm/issues)
* For support, visit kubeadm Slack Channel:
  [#kubeadm](https://kubernetes.slack.com/messages/kubeadm/)
* General SIG Cluster Lifecycle Development Slack Channel:
  [#sig-cluster-lifecycle](https://kubernetes.slack.com/messages/sig-cluster-lifecycle/)
* SIG Cluster Lifecycle [SIG information](#TODO)
* SIG Cluster Lifecycle Mailing List:
  [kubernetes-sig-cluster-lifecycle](https://groups.google.com/forum/#!forum/kubernetes-sig-cluster-lifecycle)

## Version skew policy {#version-skew-policy}

The kubeadm CLI tool of version vX.Y may deploy clusters with a control plane of version vX.Y or vX.(Y-1).
kubeadm CLI vX.Y can also upgrade an existing kubeadm-created cluster of version vX.(Y-1).

Due to that we can't see into the future, kubeadm CLI vX.Y may or may not be able to deploy vX.(Y+1) clusters.

Example: kubeadm v1.8 can deploy both v1.7 and v1.8 clusters and upgrade v1.7 kubeadm-created clusters to
v1.8.

Please also check our [installation guide](/docs/setup/independent/install-kubeadm/#installing-kubeadm-kubelet-and-kubectl)
for more information on the version skew between kubelets and the control plane.

## kubeadm works on multiple platforms {#multi-platform}

kubeadm deb/rpm packages and binaries are built for amd64, arm (32-bit), arm64, ppc64le, and s390x
following the [multi-platform
proposal](https://github.com/kubernetes/community/blob/master/contributors/design-proposals/multi-platform.md).

Only some of the network providers offer solutions for all platforms. Please consult the list of
network providers above or the documentation from each provider to figure out whether the provider
supports your chosen platform.

## Limitations {#limitations}

Please note: kubeadm is a work in progress and these limitations will be
addressed in due course.

1. The cluster created here has a single master, with a single etcd database
   running on it. This means that if the master fails, your cluster may lose
   data and may need to be recreated from scratch. Adding HA support
   (multiple etcd servers, multiple API servers, etc) to kubeadm is
   still a work-in-progress.

   Workaround: regularly
   [back up etcd](https://coreos.com/etcd/docs/latest/admin_guide.html). The
   etcd data directory configured by kubeadm is at `/var/lib/etcd` on the master.

## Troubleshooting {#troubleshooting}

If you are running into difficulties with kubeadm, please consult our [troubleshooting docs](/docs/setup/independent/troubleshooting-kubeadm/).




