Step-by-Step Guide to Build a Kubernetes Cluster on CentOS 7

Introduction

Kubernetes is Google’s open‑source container cluster management system built on Docker, providing resource scheduling, load balancing, service registration, and dynamic scaling. The article explains core concepts—Pods, Replication Controllers, Services, Labels, and Proxy—before detailing a CentOS 7 deployment of version 0.6.2.

Core Concepts

Pods : the smallest deployable unit, which may contain one or more containers.

Replication Controllers : ensure a specified number of pod replicas are running, recreating them on other nodes if needed.

Services : expose pods via a virtual IP and port, using iptables NAT for routing.

Labels : key/value pairs used to identify and select pods, services, and controllers.

Proxy : resolves port conflicts on a node and provides load‑balancing via random or round‑robin algorithms.

Environment Deployment

Platform versions :

CentOS 7.0

Kubernetes 0.6.2

etcd 0.4.6

Docker 1.3.2

System initialization (minimal install) and firewall configuration:

# yum -y install wget ntpdate bind-utils

# wget http://mirror.centos.org/centos/7/extras/x86_64/Packages/epel-release-7-2.noarch.rpm

# yum update

Switch from firewalld to iptables:

# systemctl stop firewalld.service

# systemctl disable firewalld.service

# yum install iptables-services

# systemctl start iptables.service

# systemctl enable iptables.service

Install etcd on the master (192.168.1.10):

# mkdir -p /home/install && cd /home/install

# wget https://github.com/coreos/etcd/releases/download/v0.4.6/etcd-v0.4.6-linux-amd64.tar.gz

# tar -zxvf etcd-v0.4.6-linux-amd64.tar.gz

# cp etcd* /bin/

# /bin/etcd -version

# mkdir /data/etcd

# /bin/etcd -name etcdserver -peer-addr 192.168.1.10:7001 -addr 192.168.1.10:4001 -data-dir /data/etcd -peer-bind-addr 0.0.0.0:7001 -bind-addr 0.0.0.0:4001 &

# iptables -I INPUT -s 192.168.1.0/24 -p tcp --dport 4001 -j ACCEPT

# iptables -I INPUT -s 192.168.1.0/24 -p tcp --dport 7001 -j ACCEPT

Install Kubernetes via yum repository:

# curl https://copr.fedoraproject.org/coprs/eparis/kubernetes-epel-7/repo/epel-7/eparis-kubernetes-epel-7-epel-7.repo -o /etc/yum.repos.d/eparis-kubernetes-epel-7-epel-7.repo

# yum -y install kubernetes

Upgrade to v0.6.2:

# mkdir -p /home/install && cd /home/install

# wget https://github.com/GoogleCloudPlatform/kubernetes/releases/download/v0.6.2/kubernetes.tar.gz

# tar -zxvf kubernetes.tar.gz

# tar -zxvf kubernetes/server/kubernetes-server-linux-amd64.tar.gz

# cp kubernetes/server/bin/kube* /usr/bin

Verify installation: # /usr/bin/kubectl version Sample output shows client and server version 0.6.2.

Master Configuration

Configuration files reside in /etc/kubernetes:

# /etc/kubernetes/config

KUBE_ETCD_SERVERS="--etcd_servers=http://192.168.1.10:4001"

KUBE_LOGTOSTDERR="--logtostderr=true"

KUBE_LOG_LEVEL="--v=0"

KUBE_ALLOW_PRIV="--allow_privileged=false"

API server:

# /etc/kubernetes/apiserver

KUBE_API_ADDRESS="--address=0.0.0.0"

KUBE_API_PORT="--port=8080"

KUBE_MASTER="--master=192.168.1.200:8080"

KUBELET_PORT="--kubelet_port=10250"

KUBE_SERVICE_ADDRESSES="--portal_net=10.254.0.0/16"

Controller manager:

# /etc/kubernetes/controller-manager

KUBELET_ADDRESSES="--machines=192.168.1.201,192.168.1.202"

Scheduler:

# /etc/kubernetes/scheduler

KUBE_SCHEDULER_ARGS=""

Start master services:

# systemctl daemon-reload

# systemctl start kube-apiserver.service kube-controller-manager.service kube-scheduler.service

# systemctl enable kube-apiserver.service kube-controller-manager.service kube-scheduler.service

Minion Configuration

Update Docker daemon to listen on TCP:

# vi /etc/sysconfig/docker

OPTIONS=--selinux-enabled -H tcp://0.0.0.0:2375 -H fd://

Open firewall for kubelet:

# iptables -I INPUT -s 192.168.1.200 -p tcp --dport 10250 -j ACCEPT

Minion config ( /etc/kubernetes/config) mirrors the master etcd settings.

# /etc/kubernetes/kubelet

KUBELET_ADDRESS="--address=0.0.0.0"

KUBELET_PORT="--port=10250"

KUBELET_HOSTNAME="--hostname_override=192.168.1.201"

Proxy config:

# /etc/kubernetes/proxy

KUBE_PROXY_ARGS=""

Start minion services:

# systemctl daemon-reload

# systemctl enable docker.service kubelet.service kube-proxy.service

# systemctl start docker.service kubelet.service kube-proxy.service

Practical Operations

Create an LNMP replication controller using the image yorko/webserver:

{
  "id": "webserverController",
  "kind": "ReplicationController",
  "apiVersion": "v1beta1",
  "labels": {"name": "webserver"},
  "desiredState": {"replicas": 2, "replicaSelector": {"name": "webserver_pod"}, "podTemplate": {"desiredState": {"manifest": {"version": "v1beta1", "id": "webserver", "volumes": [{"name":"httpconf","source":{"hostDir":{"path":"/etc/httpd/conf"}}},{"name":"httpconfd","source":{"hostDir":{"path":"/etc/httpd/conf.d"}}},{"name":"httproot","source":{"hostDir":{"path":"/data"}}}], "containers": [{"name":"webserver","image":"yorko/webserver","command":["/bin/sh","-c","/usr/bin/supervisord -c /etc/supervisord.conf"],"volumeMounts":[{"name":"httpconf","mountPath":"/etc/httpd/conf"},{"name":"httpconfd","mountPath":"/etc/httpd/conf.d"},{"name":"httproot","mountPath":"/data"}],"cpu":100,"memory":50000000,"ports":[{"containerPort":80},{"containerPort":22}]}]},"labels":{"name":"webserver_pod"}}}}

Create the service to expose the pods:

{
  "id": "webserver",
  "kind": "Service",
  "apiVersion": "v1beta1",
  "selector": {"name": "webserver_pod"},
  "protocol": "TCP",
  "containerPort": 80,
  "port": 8080
}

After creation, verify pods and service with kubectl get pod and kubectl get services. The proxy creates NAT rules such as:

Chain KUBE-PROXY (2 references)
 pkts bytes target prot opt in out source destination
 0 0 REDIRECT tcp -- * * 0.0.0.0/0 10.254.216.51 /* webserver */ tcp dpt:8080 redir ports 40689

Access the web server via http://192.168.1.201:40689/info.php and observe load‑balancing across pod replicas.

Testing Process

Delete a pod ( fedoraapache) and observe the replication controller automatically recreating it to maintain the desired replica count.

Test hostPort behavior: specifying hostPort in a replication controller causes errors, while setting it only in the pod definition works correctly.

Ensure that the replicaSelector, pod labels, and service selector all use the same key/value pair (e.g., name=webserver_pod) for proper association.