Step-by-Step Guide to Setting Up a Kubernetes Cluster with Docker, kubeadm, and Flannel

This article provides a practical, step‑by‑step guide for building a Kubernetes cluster on three CentOS VMs (master, node1, node2) with IPs 192.168.240.58, 192.168.240.57, and 192.168.240.59.

1. Prepare the VMs

Disable the firewall and SELinux, and turn off swap:

systemctl stop firewalld

systemctl disable firewalld

setenforce 0

swapoff -a

Configure kernel parameters for iptables bridging:

cat > /etc/sysctl.d/k8s.conf <<EOF
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF

sysctl --system

2. Install Docker, kubeadm, kubelet, and kubectl

Install Docker from the Alibaba Cloud mirror:

wget https://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo -O /etc/yum.repos.d/docker-ce.repo

yum -y install docker-ce-18.06.1.ce-3.el7

systemctl enable docker && systemctl start docker

Add the Kubernetes repository:

cat > /etc/yum.repos.d/kubernetes.repo <<EOF
[kubernetes]
name=Kubernetes
baseurl=https://mirrors.aliyun.com/kubernetes/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=0
repo_gpgcheck=0
gpgkey=https://mirrors.aliyun.com/kubernetes/yum/doc/yum-key.gpg https://mirrors.aliyun.com/kubernetes/yum/doc/rpm-package-key.gpg
EOF

Install the Kubernetes binaries: yum install -y kubelet-1.18.0 kubeadm-1.18.0 kubectl-1.18.0 3. Initialize the master node

kubeadm init \
  --apiserver-advertise-address=192.168.240.58 \
  --image-repository registry.aliyuncs.com/google_containers \
  --kubernetes-version v1.18.0 \
  --service-cidr=10.96.0.0/12 \
  --pod-network-cidr=10.244.0.0/16

Set up 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

4. Join the worker nodes

The join command generated by kubeadm init should be run on each node (images illustrate the process).

5. Deploy the Flannel CNI network plugin

wget https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml

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

kubectl get pods -n kube-system

6. Create a test nginx pod and expose it

kubectl create deployment nginx --image=nginx

kubectl expose deployment nginx --port=80 --type=NodePort

Verify the service and access it via the NodePort (e.g., http://192.168.240.58:31343/).

For further details, refer to the screenshots included throughout the guide.