Creating a Kubernetes Cluster on-prem in Ubuntu

Here, we’ll show the easiest way to create a single node Kubernetes cluster on Ubuntu 16.04. This can be dones in VMs or physical machines.

Notes

• kubeadm is in alpha state and is not supposed to be used in production. This cluster should be used for tests/development.
• In production, it is recommended that the master node be exclusive for the k8s pods, and not for regular pods, as we’ll do here with taint

Hands-on

SSH to your machine. And preferrably run all the following commands as root user. Just do:

sudo su -

Install some packages

Add some source repos and install packages such as kubelet, docker and kubeadm itself. Just run the following lines:

apt-get update && apt-get install -y apt-transport-https
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 http://apt.kubernetes.io/ kubernetes-xenial main
EOF
apt-get update
apt-get install -y docker.io kubelet kubeadm kubectl kubernetes-cni

Run kubeadm

Run:

kubeadm init

Wait a couple minutes and then your cluster is almost ready.

In most cases, the default configuration of init should work. If you want to install a verstion different than the stable, you must provide the option --kubernetes-version and provide a valid version. See releases page.

For example, to install the version v1.8.0-alpha.3, just run it with:

kubeadm init --kubernetes-version='v1.8.0-alpha.3'

The output of init should look like this:

Accessing the cluster

Once completed the init, the cluster should be ready and accessible via kubectl, the Kubernetes CLI. By default, it looks for credentials in ~/.kube/config file. If you don’t have anything in there, you should hit an error.

The easisest way to get a credentials file is copying the admin.conf created by kubeadm and place it in the default location. Do it with:

mkdir ~/.kube
cp /etc/kubernetes/admin.conf ~/.kube/config

Now, you should be able to run commands such as kubectl get pods --all-namespaces.

Tainting the Master node

As stated before, master node should not receive nothing but the main Kubernetes pods, such as api-server, kube-controller-manager, cni, kube-dns and others. But as this is a dev environment, there should be no problem in marking this node as schedulable, so you can have a single node fully working cluster.

Enable scheduling of regular pods in the master with:

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

Installing a CNI plugin

Kubernetes needs a network controller, that is self-hosted and installed as a plugin. You must install a pod network add-on so that your pods can communicate with each other. Here, we’ll use Calico. To install it in a single command, just run:

kubectl apply -f https://docs.projectcalico.org/v2.5/getting-started/kubernetes/installation/hosted/kubeadm/1.6/calico.yaml

This command works for clusters of version >= 1.6. If your version is older, look for it in the calico page

If you want to see other Network plugins, look here.

Check if it works

Once you’ve installed the network plugin, you now only need to check whether all pods are running correctly. Monitor it with:

watch kubectl get pods --all-namespaces

And wait for all pods to be RUNNING.

Optional: Join other nodes

If you want more than one node in your cluster, join others after you finish the instalation of the master. In the output of kubeadm init you should see the join command. More info here.

Conclusion

And that’s it! You have a running Kubernetes cluster. To more details on this process, check the official documentation.

This tutorial is also avaiable here in my Github.