How to Install Kubernetes 1.21 on CentOS 7 / RHEL 7

What is Kubernetes?

Kubernetes is a container management tool. It is Donated by Google to the Opensource community. It has now become the defacto container management tool of choice.

In Kubernetes setup we have one master (control) node and multiple worker nodes. The worker-nodes are then managed from the master node, thus ensuring that the cluster is managed from a central point.

You can also deploy a single-node Kubernetes cluster. You can use Minikube, which is a tool that runs a single-node Kubernetes cluster in a virtual machine on your node.

For this tutorial, we will walk-through a multi-node Kubernetes cluster installation based on CentOS 7 . 

How to Install Kubernetes :

Prerequisites:

1. Multiple servers running Centos 7 (1 Master Node, 2 Worker Nodes). It is recommended that your Master Node have at least 2 CPUs.
2. Internet connectivity on all your nodes. We will be fetching kubernetes and docker packages from the repository. 
3. You will also need access to an account with sudo or root privileges. In this tutorial, I will be using my root account.

Kubernetes architecture

Installations Steps of Kubernetes 1.21 on Master Node

For Kubernetes to work, you will need a containerization engine. For this installation, we will use docker. 

Setup Hostname, Firewall and SELinux

On your master node, set the hostname and if you don’t have a DNS server, then also update your /etc/hosts file.

# hostnamectl set-hostname kubemaster
# cat <<EOF>> /etc/hosts
192.168.56.104 kubemaster
192.168.56.105 kubeworker1
192.168.56.106 kubeworker2
EOF

Next, disable SElinux and update your firewall rules or disable your firewall.

# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux
# reboot

Disable Swap in all nodes using “swapoff -a” command and remove or comment out swap partitions or swap file from fstab file.

Set the following firewall rules on ports.

# firewall-cmd --permanent --add-port=6443/tcp
# firewall-cmd --permanent --add-port=2379-2380/tcp
# firewall-cmd --permanent --add-port=10250/tcp
# firewall-cmd --permanent --add-port=10251/tcp
# firewall-cmd --permanent --add-port=10252/tcp
# firewall-cmd --permanent --add-port=10255/tcp
# firewall-cmd –reload
# modprobe br_netfilter
# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

Or you can Disable Firewall.

[root@devopszones ~]#systemctl disable  firewalld

Add the Kubernetes Repo

You will need to add Kubernetes repositories manually as they do not come installed by default on CentOS 7.

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
EOF

Install Kubeadm and Docker

# yum install kubeadm docker -y 

When the installation completes successfully, enable and start both the services.

# systemctl enable kubelet &&  systemctl start kubelet
# systemctl enable docker &&  systemctl start docker

Initialize Kubernetes Master

Initializing Kubernetes master is a fully automated process that is managed by the “kubeadm init“ command which you will run.

# kubeadm init --control-plane-endpoint 192.168.56.104

Kubeadm init

Initialize Kubernetes master

 kubelet: failed to run Kubelet: failed to create kubelet: misconfiguration: kubelet cgroup driver: "systemd" is different from docker cgroup driver: "cgroupfs"

As we can see in the output that kubernetes master has been initialized successfully. Execute the beneath commands to use the cluster as root user.

[root@devopszones ~]# mkdir -p $HOME/.kube
[root@devopszones ~]# sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
[root@devopszones ~]# sudo chown $(id -u):$(id -g) $HOME/.kube/config

Deploy a pod network to the cluster

To make the cluster status readyrunning, deploy the pod network so that containers of different host communicated each other.  POD network is the overlay network between the worker nodes.

Run the Following command to deploy network.

[root@devopszones ~]#kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$(kubectl version | base64 | tr -d '\n')"
serviceaccount/weave-net created
clusterrole.rbac.authorization.k8s.io/weave-net created
clusterrolebinding.rbac.authorization.k8s.io/weave-net created
role.rbac.authorization.k8s.io/weave-net created
rolebinding.rbac.authorization.k8s.io/weave-net created
daemonset.apps/weave-net created
[root@devopszones ~]#

Now run the following commands to verify the status

[root@devopszones ~]#kubectl get pods -A
NAMESPACE     NAME                                 READY   STATUS    RESTARTS   AGE
kube-system   coredns-558bd4d5db-4c6d7             1/1     Running   0          5m5s
kube-system   coredns-558bd4d5db-d7995             1/1     Running   0          5m5s
kube-system   etcd-kubemaster                      1/1     Running   0          5m2s
kube-system   kube-apiserver-kubemaster            1/1     Running   0          5m11s
kube-system   kube-controller-manager-kubemaster   1/1     Running   0          5m10s
kube-system   kube-proxy-qg4js                     1/1     Running   0          5m5s
kube-system   kube-scheduler-kubemaster            1/1     Running   0          5m2s
kube-system   weave-net-skv44                      2/2     Running   0          21s
[root@devopszones ~]#
[root@devopszones ~]#kubectl get nodes
NAME          STATUS     ROLES                  AGE     VERSION
kubemaster    Ready      control-plane,master   6m57s   v1.21.3

Setting Up Worker Nodes to Join Kubernetes Cluster

The following steps will run on the worker nodes. These steps should be run on every worker node when joining the Kubernetes cluster.

Setup Hostname, Firewall and SELinux

On your master node, set the hostname and if you don’t have a DNS server, then also update your /etc/hosts file.

# hostnamectl set-hostname kubeworker1
# cat <<EOF>> /etc/hosts
192.168.56.104 kubemaster
192.168.56.105 kubeworker1
192.168.56.106 kubeworker2
EOF

Next, disable SElinux and update your firewall rules or disable your firewall.

# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux
# reboot

Disable Swap in all nodes using “swapoff -a” command and remove or comment out swap partitions or swap file from fstab file.

Set the following firewall rules on ports.

# firewall-cmd --permanent --add-port=6443/tcp
# firewall-cmd --permanent --add-port=2379-2380/tcp
# firewall-cmd --permanent --add-port=10250/tcp
# firewall-cmd --permanent --add-port=10251/tcp
# firewall-cmd --permanent --add-port=10252/tcp
# firewall-cmd --permanent --add-port=10255/tcp
# firewall-cmd –reload
# modprobe br_netfilter
# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

Or you can Disable Firewall.

[root@devopszones ~]#systemctl disable  firewalld

Add the Kubernetes Repo

You will need to add Kubernetes repositories manually as they do not come installed by default on CentOS 7.

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
EOF

Install Kubeadm and Docker

# yum install kubeadm docker -y 

When the installation completes successfully, enable and start both the services.

# systemctl enable kubelet &&  systemctl start kubelet
# systemctl enable docker &&  systemctl start docker

Join the Worker Node to the Kubernetes Cluster

We now require the token that kubeadm init generated, to join the cluster. You can copy and paste it to your kubeworker1 and kubeworker2 if you had copied it somewhere.

[root@devopszones ~]#kubeadm join 192.168.56.104:6443 --token sqs3wu.k5dacuzfzc1f4uro \
>         --discovery-token-ca-cert-hash sha256:00a0029c032bfb3d06516a27340e5e552d6ec8da9c70d4c3908ea5b0cd230aee

Kubernetes worker node join

Do the same thing for other Worker node.

Problem joining node to Kubernetes cluster:  dial tcp 127.0.0.1:10248: connect: connection refused.

Now verify Nodes status from master node using kubectl command

[root@devopszones ~]#kubectl get nodes
NAME          STATUS   ROLES                  AGE   VERSION
kubemaster    Ready    control-plane,master   72m   v1.21.3
kubeworker1   Ready    <none>                 66m   v1.21.3
kubeworker2   Ready    <none>                 64m   v1.21.3
[root@devopszones ~]#

Now we have successfully joined two worker nodes to the cluster. You can now begin to create your pods and deploy your services. Please find the video guide below. Please share the article to help others.