Three Nodes Kubernetes Installation on Centos 7

Prerequisites

2 min readApr 21, 2019

Disable swap in all nodes

swapoff -a
Remove swap entry from /etc/fstab.

Min: 2GB memory, 2 CPUs per node.
Install docker on all nodes.

yum -y install docker
systemctl enable docker
systemctl start docker

All hosts file should be same and include all nodes hostnames.

192.168.1.60 kubemaster01
192.168.1.61 kubeworker01
192.168.1.62 kubeworker02

Set these kernel parameters on all nodes.

cat <<EOF > /etc/sysctl.d/k8s.conf
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
sysctl -p

Configure Repository

Do this on all nodes.

cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[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
exclude=kube*
EOF

Install Kubernetes Packages

Install packages on all nodes.

yum install -y kubelet kubeadm kubectl --disableexcludes=kubernetes
systemctl enable kubelet 
systemctl start kubelet

Initialize Kubernetes Master

This command is for weave overlay network. There should be — pod-network-cidr parameter for other networks.

kubeadm init

There will an output like that;

......To start using your cluster, you need to run the following 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 options listed at:
  https://kubernetes.io/docs/concepts/cluster-administration/addons/

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

kubeadm join 192.168.1.10:6443 --token d1dyaj.31zxywbg93s1ywjy --discovery-token-ca-cert-hash sha256:71a91721595fde66b6382908d801266602a14de8e16bdb7a3cede21509427009

Run these commands in the terminal to manage and work on the cluster as a regular user. “kubeadm join…” command will be used for to add worker nodes. Write it down.

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

Check pods in cluster.

kubectl get pods --all-namespaces

There should be core-dns pods in pending state. A pod network should be installed to make them ready.

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

Check pods again and all pods should be ready.

Adding Nodes

Nodes can be added with “kubeadm join…” command which was given in init output.

kubeadm join 192.168.1.10:6443 --token d1dyaj.31zxywbg93s1ywjy --discovery-token-ca-cert-hash sha256:71a91721595fde66b6382908d801266602a14de8e16bdb7a3cede21509427009

Now all nodes should be ready when it is checked from master node.

kubectl get nodes

If you forget to write down join command, you can get it again with this;

kubeadm token create — print-join-command