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Creating a single master cluster with kubeadm

kubeadm helps you bootstrap a minimum viable Kubernetes cluster that conforms to best practices. With kubeadm, your cluster should pass Kubernetes Conformance tests. Kubeadm also supports other cluster lifecycle functions, such as upgrades, downgrade, and managing 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:

kubeadm’s overall feature state is Beta.

Before you begin

Objectives

Instructions

Installing kubeadm on your hosts

See “Installing kubeadm”.

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.

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.
  2. (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:

kubeadm init <args>

More information

For more information about kubeadm init arguments, see the kubeadm reference guide.

For a complete list of configuration options, see the configuration file documentation.

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.

To run kubeadm init again, you must first tear down the cluster.

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:

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:

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.

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.

Installing a pod network add-on

Caution: This section contains important information about installation and deployment order. Read it carefully before proceeding.

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. See the add-ons page for a complete list of available network add-ons. - IPv6 support was added in CNI v0.6.0. - CNI bridge and local-ipam 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. Make sure that your network manifest supports RBAC.

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

kubectl apply -f <add-on.yaml>

You can install only one pod network per cluster.

Please select one of the tabs to see installation instructions for the respective third-party Pod Network Provider.

For more information about using Calico, see Quickstart for Calico on Kubernetes, Installing Calico for policy and networking, 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.

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

Canal uses Calico for policy and Flannel for networking. Refer to the Calico documentation for the official getting started guide.

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.

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

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.

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 .

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.

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.

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.

The official Romana set-up guide is here.

Romana works on amd64 only.

kubectl apply -f https://raw.githubusercontent.com/romana/romana/master/containerize/specs/romana-kubeadm.yml

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.

The official Weave Net set-up guide is here.

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.

kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"

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.

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:

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

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

kubeadm join --token <token> <master-ip>:<master-port> --discovery-token-ca-cert-hash sha256:<hash>
Note: To specify an IPv6 tuple for <master-ip>:<master-port>, IPv6 address must be enclosed in square brackets, for example: [fd00::101]:2073.

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:

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

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.

(Optional) Proxying API Server to localhost

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

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

To undo what kubeadm did, you should first drain the node and make sure that the node is empty before shutting it down.

Talking to the master with the appropriate credentials, run:

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:

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.

Maintaining a cluster

Instructions for maintaining kubeadm clusters (e.g. upgrades,downgrades, etc.) can be found here.

Explore other add-ons

See the list of add-ons to explore other add-ons, including tools for logging, monitoring, network policy, visualization & control of your Kubernetes cluster.

What’s next

Feedback

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 for more information on the version skew between kubelets and the control plane.

kubeadm works on multiple platforms

kubeadm deb/rpm packages and binaries are built for amd64, arm (32-bit), arm64, ppc64le, and s390x following the multi-platform proposal.

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

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. The etcd data directory configured by kubeadm is at /var/lib/etcd on the master.

Troubleshooting

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

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