October 30, 2019 ( last updated : October 29, 2019 )
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https://github.com/gridgentoo/zookeeper-release

Abstract

Kubernetes is an open source platform for managing containerized applications developed by Google. It allows you to manage, scale, and automatically deploy your containerized applications in the clustered environment. With Kubernetes, we can orchestrate our containers across multiple hosts, scale the containerized applications with all resources on the fly, and have centralized container management environment.

In this tutorial, I will show you step-by-step how to install and configure Kubernetes on CentOS 7. We will be using 1 server 'k8s-master' as the Kubernetes Host Master, and 2 servers as Kubernetes node, 'node01' and 'node02'.

Prerequisites

3 CentOS 7 Servers
10.0.15.10 k8s-master
10.0.15.21 node01
10.0.15.22 node02
Root privileges

What we will do?

Kubernetes Installation
Kubernetes Cluster Initialization
Adding node01 and node02 to the Cluster

Kubernetes Installation

In this first step, we will prepare those 3 servers for Kubernetes installation, so run all commands on the master and node servers.

We will prepare all servers for Kubernetes installation by changing the existing configuration on servers, and also installating some packages, including docker-ce and kubernetes itself.

Configure Hosts

Edit hosts file on all server using the vim editor.

vim /etc/hosts

Paste the host's list below.

10.0.15.10      k8s-master
10.0.15.21      node01
10.0.15.22      node02

Save and exit.

Disable SELinux

In this tutorial, we will not cover about SELinux configuration for Docker, so we will disable it.

Run the command below to disable SELinux.

setenforce 0
sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux

Enable br_netfilter Kernel Module

The br_netfilter module is required for kubernetes installation. Enable this kernel module so that the packets traversing the bridge are processed by iptables for filtering and for port forwarding, and the kubernetes pods across the cluster can communicate with each other.

Run the command below to enable the br_netfilter kernel module.

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

Disable SWAP

Disable SWAP for kubernetes installation by running the following commands.

swapoff -a

And then edit the '/etc/fstab' file.

vim /etc/fstab

Comment the swap line UUID as below.

Install Docker CE

Install the latest version of Docker-ce from the docker repository.

Install the package dependencies for docker-ce.

yum install -y yum-utils device-mapper-persistent-data lvm2

Add the docker repository to the system and install docker-ce using the yum command.

yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
yum install -y docker-ce

Wait for the docker-ce installation.

Install Kubernetes

Add the kubernetes repository to the centos 7 system by running the following command.

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

Now install the kubernetes packages kubeadm, kubelet, and kubectl using the yum command below.

yum install -y kubelet kubeadm kubectl

After the installation is complete, restart all those servers.

sudo reboot

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

Change the cgroup-driver

We need to make sure the docker-ce and kubernetes are using same 'cgroup'.

Check docker cgroup using the docker info command.

docker info | grep -i cgroup

And you see the docker is using 'cgroupfs' as a cgroup-driver.

Now run the command below to change the kuberetes cgroup-driver to 'cgroupfs'.

sed -i 's/cgroup-driver=systemd/cgroup-driver=cgroupfs/g' /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

Reload the systemd system and restart the kubelet service.

systemctl daemon-reload
systemctl restart kubelet

Now we're ready to configure the Kubernetes Cluster.

Kubernetes Cluster Initialization

In this step, we will initialize the kubernetes master cluster configuration.

Move the shell to the master server 'k8s-master' and run the command below to set up the kubernetes master.

kubeadm init --apiserver-advertise-address=10.0.15.10 --pod-network-cidr=10.244.0.0/16

initialize the kubernetes master cluster configuration

Note:

--apiserver-advertise-address = determines which IP address Kubernetes should advertise its API server on.
--pod-network-cidr = specify the range of IP addresses for the pod network. We're using the 'flannel' virtual network. If you want to use another pod network such as weave-net or calico, change the range IP address.

When the Kubernetes initialization is complete, you will get the result as below.

Note:

Copy the 'kubeadm join ... ... ...' command to your text editor. The command will be used to register new nodes to the kubernetes cluster.

Now in order to use Kubernetes, we need to run some commands as on the result.

Create new '.kube' configuration directory and copy the configuration 'admin.conf'.

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

Next, deploy the flannel network to the kubernetes cluster using the kubectl command.

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

The flannel network has been deployed to the Kubernetes cluster.

Wait for a minute and then check kubernetes node and pods using commands below.

kubectl get nodes
kubectl get pods --all-namespaces

And you will get the 'k8s-master' node is running as a 'master' cluster with status 'ready', and you will get all pods that are needed for the cluster, including the 'kube-flannel-ds' for network pod configuration.

Make sure all kube-system pods status is 'running'.

Kubernetes cluster master initialization and configuration has been completed.

Adding node01 and node02 to the Cluster

In this step, we will add node01 and node02 to join the 'k8s' cluster.

Connect to the node01 server and run the kubeadm join command as we copied on the top.

kubeadm join 10.0.15.10:6443 --token vzau5v.vjiqyxq26lzsf28e --discovery-token-ca-cert-hash sha256:e6d046ba34ee03e7d55e1f5ac6d2de09fd6d7e6959d16782ef0778794b94c61e

Connect to the node02 server and run the kubeadm join command as we copied on the top.

kubeadm join 10.0.15.10:6443 --token vzau5v.vjiqyxq26lzsf28e --discovery-token-ca-cert-hash sha256:e6d046ba34ee03e7d55e1f5ac6d2de09fd6d7e6959d16782ef0778794b94c61e

Wait for some minutes and back to the 'k8s-master' master cluster server check the nodes and pods using the following command.

kubectl get nodes
kubectl get pods --all-namespaces

Now you will get node01 and node02 has been added to the cluster with status 'ready'.

node01 and node02 have been added to the kubernetes cluster.

Testing Create First Pod

In this step, we will do a test by deploying the Nginx pod to the kubernetes cluster. A pod is a group of one or more containers with shared storage and network that runs under Kubernetes. A Pod contains one or more containers, such as Docker container.

kubectl create deployment nginx --image=nginx

To see details of the 'nginx' deployment sepcification, run the following command.

kubectl describe deployment nginx

And you will get the nginx pod deployment specification.

Next, we will expose the nginx pod accessible via the internet. And we need to create new service NodePort for this.

Run the kubectl command below.

kubectl create service nodeport nginx --tcp=80:80

Make sure there is no error. Now check the nginx service nodeport and IP using the kubectl command below.

kubectl get pods
kubectl get svc

Now you will get the nginx pod is now running under cluster IP address '10.160.60.38' port 80, and the node main IP address '10.0.15.x' on port '30691'.

From the 'k8s-master' server run the curl command below.