Kubernetes is a tool for automating deployment, scaling, and management of containerized applications. It allows you to easily launch applications in containers and manage their lifecycle.

To test and deploy applications, we need a configured Kubernetes cluster. In this article, we will look at deploying a cluster on a single server (single-node cluster) and on several nodes (multi-node cluster), explain the nuances of installation and configuration, and also show how to run a test application.

In this instruction, our server will act as a master node, to which other nodes will then connect.

Server requirements

Before you begin, you need to make sure that your server meets the minimum requirements:

• OS: Ubuntu 22.04 or CentOS 8 (Ubuntu is preferable, as it has better Kubernetes support);
• Processor: 4 cores or higher;
• RAM: minimum 8 GB (for multi-node clusters, 16 GB or more is recommended);
• Disk: minimum 50 GB of free space;
• Network connection: static IP and open ports (6443, 10250, 10255, 30000-32767 and others).
• Kubernetes requires swap to be disabled, otherwise kubelet will not work. This is implemented by default on our VPS.

For stable operation of the Kubernetes master node, we recommend servers with a tariff of at least Cloud-8.

Step-by-step instructions

Kubernetes uses the Docker container engine to run containers.

Installing Docker

• Update packages and install Docker:

sudo apt update && sudo apt install -y docker.io

• Check Docker version:

docker --version

• Add Docker to autostart:

sudo systemctl enable --now docker

• Add current user to Docker group (to avoid using sudo when running containers):

sudo usermod -aG docker $USER
newgrp docker

• Check Docker operation:

docker run hello-world

If it displays a message about correct installation, then it works:

Installing Kubernetes

• Adding the Kubernetes repository:

sudo apt update && sudo apt install -y apt-transport-https curl
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list

• Install Kubernetes components:

sudo apt update && sudo apt install -y kubelet kubeadm kubectl

• Add to startup:

sudo systemctl enable --now kubelet

• Check the Kubernetes version:

kubectl version --client

Cluster setup

• Initialize the cluster (only for master node):

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

After successful initialization, a command to connect worker nodes (kubeadm join) will appear. Save it.

• To work with the cluster, configure kubectl:

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

• Check functionality:

kubectl get nodes

A master node should appear (Ready will appear after installing the network plugin):

Installing the network plugin

To enable pods to communicate, install the network plugin. For example, Flannel:

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

After a minute, check the nodes:

kubectl get nodes

The master node should now be in the Ready state:

Adding worker nodes

On each worker node, install Docker and Kubernetes, then run the kubeadm join command obtained during master node initialization:

sudo kubeadm join <master-ip>:6443 --token <token> --discovery-token-ca-cert-hash <hash>

Check that the nodes have connected:

kubectl get nodes

Deploying a test application

Create a deployment.yaml file:

apiVersion: apps/v1
kind: Deployment
metadata:
name: nginx-deployment
spec:
replicas: 2
selector:
matchLabels:
app: nginx
template:
metadata:
labels:
app: nginx
spec:
containers:
- name: nginx
image: nginx:latest
ports:
- containerPort: 80

Applying the manifest:

kubectl apply -f deployment.yaml

Checking:

kubectl get pods

If you see running pods, then everything is configured correctly.

Conclusion

Now you have a ready-made server for testing and deploying applications on Kubernetes. We looked at installing, configuring and running a test application.

Next steps may include:

• Set up a load balancer (ingress-nginx).

• Add monitoring (Prometheus, Grafana).

• Explore configuration management (ConfigMaps, Secrets).

• Set up CI/CD for automated deployment.