Kubernetes installation on CentOS7 Vagrant boxes Manually

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This page is updated in 2022 with new instructions which works for Rocky LInux as well!
As we have seen and had a setup that Docker EE installation on CentOS7. A year ago when I have worked on Kubernetes setup on the Ubuntu Linux that virtualization included all the steps involved in Docker installation to Kubernetes cluster configuration everything automated within Vagrantfile.


Kubernetes Cluster on your Desktop or Laptop or Mac book


In this post, I would like to share the manual steps that work to build a Kubernetes Cluster on CentOS7. We will be using the Docker EE installed nodes to install Kubernetes. So bringing up vagrant boxes the same thing that we had discussed earlier post proceed further.

Step 1: Check the System requirements

We have three nodes: master, node1, node2.

On ALL Nodes:
CPU Cores  2,
RAM size- 2GB Minimum 4GB good
Otherwise, Master node make it 3GB, Slave nodes with 1.5GB also a wise plan if you have limited resources.
Preparing the host mappings for master and worker nodes, Here I'm using sample names you can change as per your project needs. 
   
hostnamectl set-hostname master-node
cat << EOF >> /etc/hosts
	10.128.0.27 master-node
	10.128.0.29 node-1 worker-node-1
	10.128.0.30 node-2 worker-node-2
EOF
Setup the firewall rules 
 
  # master box run this
  sudo firewall-cmd --zone=public --permanent --add-port={6443,2379,2380,10250,10251,10252}/tcp
  
  # worker box firewall settings 
  sudo firewall-cmd --zone=public --permanent --add-port={10250,10251}/tcp
  
  #for both boxes
  firewall-cmd –reload
  modprobe br_netfilter
  echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

Step 2: Why do we need to do swap disable?

All Kubernetes masters and nodes are expected to have swap disabled. This is recommended by Kubernetes community for deployments. If swap is not disabled, kubelet service will not start on the masters and nodes,

 
# check swap available 
free -m
# if exists then run the following commands
swapoff -a # must for gcloud and aws instances
# permanent swap off from fstab
vi /etc/fstab --> comment swap entry

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


 
yum update -y
systemctl disable firewalld
systemctl stop firewalld
vi /etc/selinux/config ---> disabled

Restart all of the boxes 
 
init 6

Now install Docker if you have not installed yet! this following will installs Docker-CE. 
 
yum install docker -y
systemctl status docker #if it is inactive do the following
systemctl enable docker
systemctl start docker
systemctl start docker # make sure it is active state

Step 4: Add Kubernetes Repo 

This repo setting for CentOS boxes on ANY cloud env will works and same will work on vagrant box as well. 
 
vi /etc/yum.repos.d/kubernetes.repo

Enter the following content into the file 
 
[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

Step 5: Install kubeadm, kubelet, kubectl and start

Now run the following yum installation commands on every node.
 
yum install kubeadm -y #This will includes kubectl, kubelet part of kubeadmin installation

systemctl enable kubelet
systemctl start kubelet
systemctl status kubelet # ensure kubelet is in active state

After starting kubeadm you will get the following:
Kubernetes Installation


output

Let's configure bridge network for Kubernetes 
 
vi /etc/sysctl.d/k8s.conf
Enter the following lines 
 
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1

After file saving run the following command in the command shell. 
 
sysctl --system

In the Master node execute the following command for Kubernetes Cluster initialization: 

 
# NOTE: Please use your host IP address here
# This will do
kubeadm init

#alternatively try
kubeadm init --pod-network-cidr=192.148.0.0/16 --apiserver-advertise-address=192.168.33.100

(OR)

#To ignore preflight checks
kubeadm init --pod-network-cidr=192.148.0.0/16 --apiserver-advertise-address=192.168.33.100 --ignore-preflight-errors=Hostname,SystemVerification,NumCPU


On the Worker / Slave nodes: 
 
kubeadm join 192.168.33.100:6443 --token h1ufen.hvs0nr49ua0my7u8 \
    --discovery-token-ca-cert-hash sha256:0bc179854b5c759333360737ff53ca2c4246b61823b033ecbac50593a9c334f6

Kubernetes Worker joining

On the master node do the following: 
 
vi /etc/profile
export KUBECONFIG=/etc/kubernetes/admin.conf
Run the following: source /etc/profile
(OR) 
 
 mkdir -p $HOME/.kube
 cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
 chown $(id -u):$(id -g) $HOME/.kube/config

Now
flannel network
 
kubectl get nodes # all nodes NotReady state
kubectl get pods --all-namespaces
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

kubectl get pods --all-namespaces
kubectl get nodes

Get the status of the node in the Kubernetes cluster, after all pods Running

Validate with Deployment 

Let us validate the Kubernetes Cluster Ready for deploy web application

Step 1 Let's take nginx image for deployment creation on the Kubernetes cluster
 
 kubectl create deployment mynginx --image=nginx
First Kubernetes deployment : create deployment

Now let's see the description of the above 'mynginx' deployment.

Describe Kubernetes deployment

Scale the 'mynginx' application deployment upto 3
 
 kubectl scale --replicas=3 deployment/mynginx

Scale deployment on Kubernetes Cluster

List of all pods in the Kubernetes cluster
 
 kubectl get po
 kubectl get po -o wide

get the list of pods in Kubernetes

Next step is Create service using 'mynginx' deployment.
 
kubectl create service nodeport mynginx --tcp=8080:80

kubectl get services

Service creation in Kubernetes Cluster
all set to go for checking in the browser
http://192.168.33.110:32286/


As our slave node running on 192.168.33.110 and the node port exposed as 32286.

Here I conclude our Kubernetes cluster working as expected! Please post your comments or suggestions to improve our learnings more useful to many other starters.

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