website/docs/getting-started-guides/kubeadm.md

Overview

This quickstart shows you how to easily install a secure Kubernetes cluster on machines running Ubuntu 16.04 or CentOS 7. The installation uses a tool called kubeadm which is part of Kubernetes 1.4.

This process works with local VMs, physical servers and/or cloud servers. It is simple enough that you can easily integrate its use into your own automation (Terraform, Chef, Puppet, etc).

The kubeadm tool is currently in alpha but please try it out and give us feedback!

Prerequisites

1. One or more machines running Ubuntu 16.04 or CentOS 7
2. 1GB or more of RAM per machine (any less will leave little room for your apps)
3. Full network connectivity between all machines in the cluster (public or private network is fine)

Objectives

• Install a secure Kubernetes cluster on your machines
• Install a pod network on the cluster so that application components (pods) can talk to each other
• Install a sample microservices application (a socks shop) on the cluster

Instructions

(1/4) Installing kubelet and kubeadm on your hosts

You will install the following packages on all the machines:

• docker: the container runtime, which Kubernetes depends on.
• kubelet: the most core component of Kubernetes. It runs on all of the machines in your cluster and does things like starting pods and containers.
• kubectl: the command to control the cluster once it's running. You will only use this on the master.
• kubeadm: the command to bootstrap the cluster.

For each host in turn:

• SSH into the machine and become root if you are not already (for example, run sudo su -).

• If the machine is running Ubuntu 16.04, run:

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

  If the machine is running CentOS 7, run:

  # cat <<EOF > /etc/yum.repos.d/kubernetes.repo
  [kubernetes]
  name=Kubernetes
  baseurl=http://yum.kubernetes.io/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
  EOF
  # setenforce 0
  # yum install -y docker kubelet kubeadm kubectl kubernetes-cni
  # systemctl enable docker && systemctl start docker
  # systemctl enable kubelet && systemctl start kubelet
  

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

Note: setenforce 0 will no longer be necessary on CentOS once #33555 is included in a released version of kubeadm.

(2/4) 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). All of these components run in pods started by kubelet.

To initialize the master, pick one of the machines you previously installed kubelet and kubeadm on, and run:

 # kubeadm init

Note: this will autodetect the network interface to advertise the master on as the interface with the default gateway. If you want to use a different interface, specify --api-advertise-addresses=<ip-address> argument to kubeadm init.

This will download and install the cluster database and "control plane" components. This may take several minutes.

The output should look like:

<master/tokens> generated token: "f0c861.753c505740ecde4c"
<master/pki> created keys and certificates in "/etc/kubernetes/pki"
<util/kubeconfig> created "/etc/kubernetes/kubelet.conf"
<util/kubeconfig> created "/etc/kubernetes/admin.conf"
<master/apiclient> created API client configuration
<master/apiclient> created API client, waiting for the control plane to become ready
<master/apiclient> all control plane components are healthy after 61.346626 seconds
<master/apiclient> waiting for at least one node to register and become ready
<master/apiclient> first node is ready after 4.506807 seconds
<master/discovery> created essential addon: kube-discovery
<master/addons> created essential addon: kube-proxy
<master/addons> created essential addon: kube-dns

Kubernetes master initialised successfully!

You can connect any number of nodes by running:

kubeadm join --token <token> <master-ip>

Make a record of the kubeadm join command that kubeadm init outputs. You will need this in a moment. The key included here is secret, keep it safe — anyone with this key can add authenticated nodes to your cluster.

The key is used for mutual authentication between the master and the joining nodes.

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, for example if you want a single-machine Kubernetes cluster for development, run:

# kubectl taint nodes --all dedicated-
node "test-01" tainted
taint key="dedicated" and effect="" not found.
taint key="dedicated" and effect="" not found.

This will remove the "dedicated" taint from any nodes that have it, including the master node, meaning that the scheduler will then be able to schedule pods everywhere.

(3/4) Joining your nodes

The nodes are where your workloads (containers and pods, etc) run. If you want to add any new machines as nodes to your cluster, for each machine: SSH to that machine, become root (e.g. sudo su -) and run the command that was output by kubeadm init. For example:

# kubeadm join --token <token> <master-ip>
<util/tokens> validating provided token
<node/discovery> created cluster info discovery client, requesting info from "http://138.68.156.129:9898/cluster-info/v1/?token-id=0f8588"
<node/discovery> cluster info object received, verifying signature using given token
<node/discovery> cluster info signature and contents are valid, will use API endpoints [https://138.68.156.129:443]
<node/csr> created API client to obtain unique certificate for this node, generating keys and certificate signing request
<node/csr> received signed certificate from the API server, generating kubelet configuration
<util/kubeconfig> created "/etc/kubernetes/kubelet.conf"

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 that running kubectl get nodes on the master shows a cluster with as many machines as you created.

YOUR CLUSTER IS NOT READY YET!

Before you can deploy applications to it, you need to install a pod network.

(4/4) Installing a pod network

You must install a pod network add-on so that your pods can communicate with each other when they are on different hosts. It is necessary to do this before you try to deploy any applications to your cluster.

Several projects provide Kubernetes pod networks. You can see a complete list of available network add-ons on the add-ons page.

By way of example, you can install Weave Net by logging in to the master and running:

# kubectl apply -f https://git.io/weave-kube
daemonset "weave-net" created

If you prefer Calico or Canal, please refer to their respective installation guides. You should only install one pod network per cluster.

Once a pod network has been installed, you can confirm that it is working by checking that the kube-dns pod is Running in the output of kubectl get pods --all-namespaces. This signifies that your cluster is ready.

(Optional) Installing a sample application

As an example, install a sample microservices application, a socks shop, to put your cluster through its paces. To learn more about the sample microservices app, see the GitHub README.

# git clone https://github.com/microservices-demo/microservices-demo
# kubectl apply -f microservices-demo/deploy/kubernetes/manifests

You can then find out the port that the NodePort feature of services allocated for the front-end service by running:

# kubectl describe svc front-end -n sock-shop
Name:                   front-end
Namespace:              sock-shop
Labels:                 name=front-end
Selector:               name=front-end
Type:                   NodePort
IP:                     100.66.88.176
Port:                   <unset> 80/TCP
NodePort:               <unset> 31869/TCP
Endpoints:              <none>
Session Affinity:       None

It takes several minutes to download and start all the containers, watch the output of kubectl get pods -n sock-shop to see when they're all up and running.

Then go to the IP address of your cluster's master node in your browser, and specify the given port. So for example, http://<master_ip>:<port>. In the example above, this was 31869, but it is a different port for you.

If there is a firewall, make sure it exposes this port to the internet before you try to access it.

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

• Learn more about Kubernetes concepts and kubectl in Kubernetes 101.
• Install Kubernetes with a cloud provider configurations to add Load Balancer and Persistent Volume support.

Cleanup

• To uninstall the socks shop, run kubectl delete -f microservices-demo/deploy/kubernetes/manifests on the master.

• To undo what kubeadm did, simply delete the machines you created for this tutorial, or run the script below and then uninstall the packages.

  systemctl stop kubelet;
  docker rm -f $(docker ps -q); mount | grep "/var/lib/kubelet/*" | awk '{print $3}' | xargs umount 1>/dev/null 2>/dev/null;
  rm -rf /var/lib/kubelet /etc/kubernetes /var/lib/etcd /etc/cni;
  ip link set cbr0 down; ip link del cbr0;
  ip link set cni0 down; ip link del cni0;
  systemctl start kubelet

Feedback

• Slack Channel: #sig-cluster-lifecycle
• Mailing List: kubernetes-sig-cluster-lifecycle
• GitHub Issues: please tag kubeadm issues with @kubernetes/sig-cluster-lifecycle

Limitations

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

1. The cluster created here doesn't have cloud-provider integrations, so for example won't work with (for example) Load Balancers (LBs) or Persistent Volumes (PVs). To easily obtain a cluster which works with LBs and PVs Kubernetes, try the "hello world" GKE tutorial or one of the other cloud-specific installation tutorials.

   Workaround: use the NodePort feature of services for exposing applications to the internet.

2. 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 loses its configuration data and will 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.

3. kubectl logs is broken with kubeadm clusters due to #22770.

   Workaround: use docker logs on the nodes where the containers are running as a workaround.

4. There is not yet an easy way to generate a kubeconfig file which can be used to authenticate to the cluster remotely with kubectl on, for example, your workstation.

   Workaround: copy the kubelet's kubeconfig from the master: use scp root@<master>:/etc/kubernetes/admin.conf . and then e.g. kubectl --kubeconfig ./admin.conf get nodes from your workstation.