Kubernetes cluster configuration and set up.

This post will explain about configuring a three node kubernetes cluster in CentOS machine.

Before you begin i will give you a basic idea about what we are going to achieve here.

Kubernetes is an open source container management system that will help us to deploy containers and scale them according to our requirement.If you need to create a 2 node cluster with some applications we can configure that with the help of kubernetes. Kubernetes master will take care of all the resource allocation and maintenance of the containers deployed in the cluster.

In this tutorial i am setting up a two node cluster using  three CentOS machines. Please not you need to have root access to complete the steps described and you need to run till step 8 in all the nodes.

Step 1: Identify the ip address and Host name of the machines that we are going to configure

10.1.X.X -- Machine host name 1 -- > Kubernetes Master

10.1.X.X -- Machine host name 2 -- > Kubernetes Slave Node 1

10.1.X.X -- Machine host name 3 -- > Kubernetes Slave Node 2

Step 2: Edit /etc/hosts file in all the three machines and add the three ip address

Eg: 

10.1.x.x Host_name_1

10.1.x.x Host_name_2

10.1.x.x Host_name_3

Step 3: Do a yum update

#sudo yum update

Step 4: Do some other configurations in the machine using the below commands

sudo setenforce 0

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

sudo modprobe br_netfilter

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

sudo swapoff –a

sudo vim /etc/fstab

in fstab check are you able to see the UUID

then exit from the editor

Step 5: Install Docker

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

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

sudo yum install -y docker-ce

Step 6:  Install Kubernetes

Add the kubernetes repository to the centos 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.

sudo yum install -y kubelet kubeadm kubectl

Step 7: Reboot the machine 

#sudo reboot

Step 8: Start Docker and Kubernetes

systemctl start docker && systemctl enable docker

systemctl start kubelet && systemctl enable kubelet

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.

Step 9: 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=10.1.X.X --pod-network-cidr=10.244.0.0/16

Note:

--apiserver-advertise-address = determines which IP address Kubernetes should advertise its API server on(Master server).

--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.

As shown in the command window you can use the kubeadm join command to join nodes to the cluster. Save this join token number for future use. If you need to add one more node to the existing cluster you can run this command on the salve node and join that node with the master.

Step 10: 

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.

Step 11:

Run the below commands to see the status of the cluster with nodes and the running pods in the container.

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.

Step 12: Adding nodes to the existing cluster.

You can use the join command that you received when initializing the cluster to add nodes to the cluster. open shell script in each slave nodes and run the join command so as shown below you can see the node are joined to your cluster.

Wait for some minutes, and back to the master cluster server check the nodes using the following command.

sudo kubectl get nodes

Now you can see the cluster is ready with one master and two slaves. From the status bar we can see the status as Ready.