Building a Kubernetes Cluster with Kubeadm

To build a cluster, you need to have master and slave nodes and dockers need to be installed.

1. Install Docker on all three nodes.keyboard_arrow_up

Do the following on all three nodes:

apt install gpg-agent


curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository \
"deb [arch=amd64] https://download.docker.com/linux/ubuntu \
$(lsb_release -cs) \
stable"
sudo apt-get update
sudo apt-get install -y docker-ce=18.06.1~ce~3-0~ubuntu
sudo apt-mark hold docker-ce

Verify that Docker is up and running with:
```
sudo systemctl status docker
```

2. Install Kubeadm, Kubelet, and Kubectl on all three nodes.keyboard_arrow_up

Install the Kubernetes components by running this on all three nodes:

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
sudo apt-get update
sudo apt-get install -y kubelet=1.12.7-00 kubeadm=1.12.7-00 kubectl=1.12.7-00
sudo apt-mark hold kubelet kubeadm kubectl

3. Bootstrap the cluster on the Kube master node.keyboard_arrow_up

On the Kube master node, do this:
```
sudo kubeadm init --pod-network-cidr=10.244.0.0/16
```
That command may take a few minutes to complete.
When it is done, set up the local kubeconfig:
```
mkdir -p $HOME/.kube
sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
sudo chown $(id -u):$(id -g) $HOME/.kube/config
```
Take note that the kubeadm init command printed a long kubeadm join command to the screen.

You will need that kubeadm join command in the next step!
Run the following commmand on the Kube master node to verify it is up and running:
```
kubectl version
```
This command should return both a Client Version and a Server Version.
Join the two Kube worker nodes to the cluster.keyboard_arrow_up
Copy the kubeadm join command that was printed by the kubeadm init command earlier, with the token and hash. Run this command on both worker nodes, but make sure you add sudo in front of it:
sudo kubeadm join $some_ip:6443 --token $some_token --discovery-token-ca-cert-hash $some_hash

Now, on the Kube master node, make sure your nodes joined the cluster successfully:
kubectl get nodes

Verify that all three of your nodes are listed. It will look something like this:

NAME STATUS ROLES AGE VERSION ip-10-0-1-101 NotReady master 30s v1.12.2 ip-10-0-1-102 NotReady 8s v1.12.2 ip-10-0-1-103 NotReady 5s v1.12.2

Note that the nodes are expected to be in the NotReady state for now.
Set up cluster networking with flannel.keyboard_arrow_up
1. Turn on iptables bridge calls on all three nodes:
  echo "net.bridge.bridge-nf-call-iptables=1" | sudo tee -a /etc/sysctl.conf sudo sysctl -p
2. Next, run this only on the Kube master node:
  kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/bc79dd1505b0c8681ece4de4c0d86c5cd2643275/Documentation/kube-flannel.yml
  
  Now flannel is installed! Make sure it is working by checking the node status again:
  
  kubectl get nodes
  
  After a short time, all three nodes should be in the Ready state. If they are not all Ready the first time you run kubectl get nodes, wait a few moments and try again. It should look something like this:
  
  NAME STATUS ROLES AGE VERSION ip-10-0-1-101 Ready master 85s v1.12.2 ip-10-0-1-102 Ready 63s v1.12.2 ip-10-0-1-103 Ready 60s v1.12.2

Building a Kubernetes Cluster with Kubeadm

Published by Aryan Nava

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