CKA Learning Series: Build K8s Cluster using Kubeadm in minutes !

Arun Kumar Singh

Nov 7, 2020·5 min read

CKA 2020 Exam Updates(Sep onwards)

Proctored exam, 15-20 hands on questions, 2 hours, 6 k8s clusters, K8s 1.19 and no multiple choice drama !

CKA exam, tests your skills in specific domains of k8s platform. Creating/managing k8s cluster using kubeadm is one of primary requirement. I have recently passed this exam and In my opinion practising on kubeadm based cluster can help you to cover a big part of exam syllabus. I suggest create your own cluster using kubeadm and practise as much as possible to get through in first attempt. This blogpost is part of series which I will be publishing in coming days to help you pass the exam.

In this post we will cover the part in which we are building a k8s cluster using kubeadm.

What you need to start -

Free cloud account or Virtual Box
3 VMs

I am using 3 VMs named —

• node-1 [Ubuntu 18.x machine / master or controlplane]
• node-2 [Ubuntu 18.x machine / worker]
• node-3 [Ubuntu 18.x machine / worker]

What are the steps -

Perform these steps on all 3 VMs. These steps deploy required component for building k8s cluster using kubeadm.

Step 1: Configure iptables to receive bridged network traffic

# add following lines in /etc/ufw/sysctl.conf filenet/bridge/bridge-nf-call-ip6tables = 1
net/bridge/bridge-nf-call-iptables = 1
net/bridge/bridge-nf-call-arptables = 1

Step 2: Make sure you have installed ebtables and ethtool. If not please install

apt-get install ebtables ethtool

Step 3: Install HTTPS-TRANSPORT component

apt-get updateapt-get install -y apt-transport-https

Step 4: Install docker

apt-get install -y docker.io

Step 5: Add K8s repo in system

curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -cat <<EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list
deb https://apt.kubernetes.io/ kubernetes-xenial main
EOF

Step 6: Install Kubeadm,Kubelet and Kubectl

apt-get update
apt-get install -y kubelet kubeadm kubectl

Step 7: If you want kubeadm cluster process fast then pull required Images in advance which will be used for controlplane. [required on master node ], otherwise you can ignore !

kubeadm config images pull

Time to create cluster -

VMs are ready, select 1 VM which we need to prepare as a master node [k8s controlplane] and others we will prepare as a worked node. In this case I will use node-1 as a master and node-2/3 as a worker node.

Initialise Cluster

kubeadm init --pod-network-cidr=192.168.0.0/16

Thats it ! Isn’t it the simplest way to deploy a k8s cluster. Your master node is getting ready now. To start using it, you can see the 3 steps mentioned in the output. Run it !

List the status of control-plane pods. If you would have pulled image in advance, you could have avoided this delay :)

Now Node-1 as a master is ready, please run the join command mentioned above as an output of create cluster command on other worker nodes. Join command adds worker node as part of cluster.

[node-2, node-3]

Did you see NotReady status on nodes ? It is because you missed to install pod network. [I miss this intentionally to help you understand troubleshooting of cluster which is an essential topic of CKA ]

Lets Install Pod Network, we will use Weave as a pod network solution. Please note there are multiple solutions so you can use anyone as per your requirement.

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

Once done check the status again on cluster.

Voila ! Cluster is ready for use :)

If by any chance you miss to copy that join command ! Don’t worry, we have solution.

# list tokens [run on node-1]kubeadm token list# if there is no token generate one kubeadm token create# generate discovery token hashopenssl x509 -pubkey -in /etc/kubernetes/pki/ca.crt | openssl rsa -pubin -outform der 2>/dev/null | openssl dgst -sha256 -hex | sed 's/^.* //'# now build up your command kubeadm join <master-node-ip>:6443 --token <token> \
--discovery-token-ca-cert-hash sha256:<token hash>

to avoid above hustle, we have one more simple solution, run following command —

kubeadm token create --print-join-command

But knowing things in details will not bite anyone.

Once your cluster is ready, you can start using it immediately. I have consolidated few commands which can help you as well.