Step-by-Step Guide to Building a Kubernetes Cluster on CentOS with Docker and Flannel

Installation Requirements (Pre‑check)

Before starting, the machines for the Kubernetes cluster must meet the following conditions:

Three machines, OS CentOS 7.5+ (minimal)

Hardware: 2 GB RAM, 2 CPUs, 30 GB disk

Installation Steps

Roles and IPs:

master – 192.168.50.128 node1 – 192.168.50.131 node2 – 192.168.50.132

2.1 Pre‑processing on All Nodes

These steps must be performed on every node (master and workers).

(1) Disable firewall and SELinux

# systemctl disable --now firewalld
# setenforce 0
# sed -i 's/enforcing/disabled/' /etc/selinux/config

(3) Disable swap

# swapoff -a
# sed -i.bak 's/^.*centos-swap/#&/g' /etc/fstab

To permanently disable swap, comment out the swap line in /etc/fstab.

(4) Set hostnames

# hostnamectl set-hostname master

# hostnamectl set-hostname node1

# hostnamectl set-hostname node2

Run bash to load the new hostnames.

(5) Add hosts entries

# cat >>/etc/hosts <<EOF
192.168.50.128 master
192.168.50.131 node1
192.168.50.132 node2
EOF

(6) Enable IPv6 forwarding

# cat > /etc/sysctl.d/k8s.conf <<EOF
net.ipv4.ip_forward = 1
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
EOF
# sysctl --system

(7) Configure yum repositories

Use Alibaba Cloud mirrors for base and epel repositories:

# mv /etc/yum.repos.d/* /tmp
# curl -o /etc/yum.repos.d/CentOS-Base.repo https://mirrors.aliyun.com/repo/Centos-7.repo
# curl -o /etc/yum.repos.d/epel.repo http://mirrors.aliyun.com/repo/epel-7.repo

(8) Set timezone and sync time

# ln -sf /usr/share/zoneinfo/Asia/Shanghai /etc/localtime
# yum install dnf ntpdate -y
# dnf makecache
# ntpdate ntp.aliyun.com

2.2 Install Docker

(1) Add Docker yum repo

# curl -o /etc/yum.repos.d/docker-ce.repo https://mirrors.aliyun.com/docker-ce/linux/centos/docker-ce.repo
# cat /etc/yum.repos.d/docker-ce.repo
[docker-ce-stable]
name=Docker CE Stable - $basearch
baseurl=https://mirrors.aliyun.com/docker-ce/linux/centos/7/$basearch/stable
enabled=1
gpgcheck=1
gpgkey=https://mirrors.aliyun.com/docker-ce/linux/centos/gpg
...

(2) Install Docker CE

# dnf list docker-ce --showduplicates

Install the latest version:

# dnf install -y docker-ce docker-ce-cli

(3) Start Docker and enable on boot

# systemctl enable --now docker

Verify version:

# docker --version
Docker version 19.03.12, build 48a66213fea

(4) Configure Docker registry mirrors

# cat > /etc/docker/daemon.json <<EOF
{"registry-mirrors": ["https://f1bhsuge.mirror.aliyuncs.com"]}
EOF
# systemctl restart docker

2.3 Install Kubernetes Components

(1) Add Kubernetes yum repo

# 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

(2) Install kubeadm, kubelet, kubectl (version 1.18.6)

# dnf install -y kubelet-1.18.6 kubeadm-1.18.6 kubectl-1.18.6

(3) Enable kubelet at boot

# systemctl enable kubelet

2.4 Deploy Kubeadm Master

(1) Generate init configuration

# kubeadm config print init-defaults > kubeadm-init.yaml

Typical kubeadm-init.yaml includes API server address, pod subnet, image repository (Alibaba Cloud), and Kubernetes version.

(2) Pre‑pull images

# kubeadm config images pull --config kubeadm-init.yaml
[config/images] Pulled registry.aliyuncs.com/google_containers/kube-apiserver:v1.18.0
... (other core images)

(3) Initialize the master

# kubeadm init --config kubeadm-init.yaml

After successful init, run as a regular user:

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

2.5 Join Worker Nodes

Execute the kubeadm join command printed at the end of the master init on each worker:

# kubeadm join 192.168.50.128:6443 --token abcdef.0123456789abcdef \
    --discovery-token-ca-cert-hash sha256:05b84c41152f72ca33afe39a7ef7fa359eec3d3ed654c2692b665e2c4810af3e

Verify nodes:

# kubectl get nodes
NAME    STATUS   ROLES   AGE   VERSION
master  Ready    master  82m   v1.18.6
node1   Ready    <none>  60m   v1.18.6
node2   Ready    <none>  55m   v1.18.6

2.6 Install Flannel Network Plugin

Flannel provides an overlay network for pods.

(1) Download manifest (adjust hosts for GitHub if needed)

# echo '199.232.28.133  raw.githubusercontent.com' >> /etc/hosts
# curl -o kube-flannel.yml https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
# sed -i 's/quay.io/quay-mirror.qiniu.com/g' kube-flannel.yml
# kubectl apply -f kube-flannel.yml

Verify pods:

# kubectl get pod -n kube-system | grep kube-flannel
kube-flannel-ds-amd64-xxxx   1/1   Running   ...

(2) If images cannot be pulled, load a pre‑saved tarball:

# docker load -i flannel.tar

2.7 Verify Cluster Health

# kubectl get nodes
NAME    STATUS   ROLES   AGE   VERSION
master  Ready    master  82m   v1.18.6
node1   Ready    <none>  60m   v1.18.6
node2   Ready    <none>  55m   v1.18.6

3 Test the Kubernetes Cluster

3.1 Deploy an Nginx Deployment

# kubectl create deployment nginx --image=nginx
# kubectl expose deployment nginx --port=80 --type=NodePort

Find the NodePort (e.g., 32627) and access the service via the worker node IP.

3.2 Install Kubernetes Dashboard

(1) Download and modify manifest

# curl -o recommended.yaml https://raw.githubusercontent.com/kubernetes/dashboard/v2.0.0-beta8/aio/deploy/recommended.yaml
# Edit the Service to type NodePort and set nodePort (e.g., 30001)
# Apply the manifest
# kubectl apply -f recommended.yaml

(2) Retrieve admin token

# kubectl -n kube-system describe secret $(kubectl -n kube-system get secret | awk '/dashboard-admin/{print $1}')

Access the dashboard at https://<worker‑node‑IP>:30001 using the token.

(3) Bind cluster‑admin role for full access

# kubectl create serviceaccount dashboard-admin -n kube-system
# kubectl create clusterrolebinding dashboard-admin --clusterrole=cluster-admin --serviceaccount=kube-system:dashboard-admin

4 Common Issues and Troubleshooting

Image pull failures : Use a compatible Kubernetes version in kubeadm-init.yaml or switch to a reachable mirror.

Docker cgroup driver mismatch : Set Docker to use systemd in /etc/docker/daemon.json and restart Docker.

kubectl on worker nodes : Copy /etc/kubernetes/admin.conf from the master to the worker and set KUBECONFIG environment variable.

Swap not disabled : Run swapoff -a and comment out swap entries in /etc/fstab.

Control‑plane components unhealthy : Remove --port=0 from kube‑controller‑manager.yaml and kube‑scheduler.yaml in /etc/kubernetes/manifests.

Dashboard cannot reach API server : Schedule the dashboard pod on the master node and comment out the default tolerations.

5 References

For further reading, see the blog post at https://www.cnblogs.com/FengGeBlog/p/10810632.html .

ZooKeeper is a classic distributed consistency solution; stay tuned for a dedicated session on September 1st.