In this series of small articles, I’ll install & configure a Kubernetes cluster with a master and a few nodes, and set up a few applications experiments.

I’ll only work with Centos 7 systems.

Installing Kubernetes

The kubernetes installation is mostly similar for both master & workers nodes, with some light differences at the end of the process.

On both Master & Worker nodes

The following tasks must be made on all nodes:

  • Upgrade all system packages;
  • Disable swap;
  • Enable bridge firewall rules;
  • Install docker-ce and its requirements;
  • Install kubernetes’ repository & kubernetes.

Upgrade all system packages

As usual, prior to any new installation, make sure your system is updated.

$ yum clean all && yum upgrade -y

Disable selinux & swap

Swap & selinux must be disabled prior installing kubernetes

$ setenforce 0
$ sed -i 's/^SELINUX=.*/SELINUX=disabled/' /tmp/config

A reboot is likely required to take changes in effect permanently.

$ sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab 
$ swapoff -a

Enable bridge firewall rules

$ modprobe br_netfilter
$ echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

Install docker-ce & its requirements

It is strongly recommended to not use the docker from the Centos repository as it can be quite old & doesn’t handle the required features for the kubernetes. Add its official repository & install it:

$ yum install -y yum-utils device-mapper-persistent-data lvm2
$ yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
$ yum install -y docker-ce
$ systemctl enable docker-ce
$ systemctl start docker-ce

Install kubernetes’ repository & kubernetes

Prepare a repo file for Kubernetes repository & install kubernetes to complete kubernetes installation. There is no need to start it, just enable it in systemd for now.

$ cat > /etc/yum.repo.d/kubernetes.repo << EOF
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/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

$ yum install -y kubelet kubeadm kubectl
$ systemctl enable kubelet

Once you’ve installed kubernetes, you’re mostly good to go. You now need to do only master-only initialization & slave-only join commands.

On Master nodes only

On master nodes, you need to initialize the kubernetes cluster & install the network layer

$ kubeadm init --pod-network-cidr=10.244.0.0/16

Note that the –pod-network-cidr argument is required because the network’ stack we will use, flannel, requires it.

Write down the join command, or store the join token. The given token has a 24h TTL, but you are still able to generate new ones using kubeadm token commands:

$ kubeadm token create
e7wy7h.62br9mqdsztr0t1g
$ kubeadm token list
TOKEN                     TTL       EXPIRES                     USAGES                   DESCRIPTION   EXTRA GROUPS
e7wy7h.62br9mqdsztr0t1g   23h       2019-05-16T14:06:24+02:00   authentication,signing   <none>        system:bootstrappers:kubeadm:default-node-token

Once initialized, you must prepare your user to be able to connect the cluster

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

And finally, install the network layer as kubernetes does not have one by default. I’ll use coreos’s flannel for now:

$ kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

On Worker nodes only

To join the cluster, reuse the given token on each nodes:

$ kubectl join --token=<given token> --discovery-token-unsafe-skip-ca-verification --master-ip=<master ip>

If joining the cluster is successfull, you’ll be able to see its status using the kubectl get nodes command on the master:

$ kubectl get nodes
NAME   STATUS   ROLES    AGE   VERSION
kub0   Ready    master   29d   v1.14.1
kub1   Ready    <none>   29d   v1.14.1
kub2   Ready    <none>   29d   v1.14.1
kub3   Ready    <none>   29d   v1.14.1
kub4   Ready    <none>   29d   v1.14.1
kub5   Ready    <none>   29d   v1.14.1

You’ll be done if all nodes are in the Ready state.