Setting Up Kubernetes Cluster on CentOS Servers.

So I’ve been running some of our development components on Docker in the company but it was never significant to the level that we rely on them for Development and Production, due to some major changes in our DataCenter I had to setup some database clusters and services from scratch to migrate our old data into.

So I saw this as an opportunity to convert some of our classic VMs into docker containers for a easier production and development experience.

For now I have prepared 3 VMS in 3 different hosts to be used by Kubernetes, all running CentOS 7 minimal.

the IP addresses of the machines are:

  • -> Kubernetes Master
  • -> Kubernetes Node1
  • -> Kubernetes Node2

Lets begin by setting up some tools on each machine.

yum install -y yum-utils device-mapper-persistent-data lvm2 git nano wget vim

now lets configure our host files for a cleaner communication between the cluster. I added the following in the end of each /etc/hosts file on each server: kubemaster kube1 kube2

now lets get rid of SELINUX, run setenforce 0 on each server and then edit /etc/sysconfig/selinux like following:

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#     enforcing - SELinux security policy is enforced.
#     permissive - SELinux prints warnings instead of enforcing.
#     disabled - No SELinux policy is loaded.
# SELINUXTYPE= can take one of three two values:
#     targeted - Targeted processes are protected,
#     minimum - Modification of targeted policy. Only selected processes are protected.
#     mls - Multi Level Security protection.

now we need to enable br_netfilter kernel module to allow packets traversing the bridge to be processed by iptables for port forwarding matters as well of communication of nodes within the cluster.

modprobe br_netfilter
echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables

Disable swap on the machines by:

swapoff -a

then edit /etc/fstab file and comment out the swap partition line.

Then install Docker

yum-config-manager \
    --add-repo \
yum install docker-ce
systemctl start docker && systemctl enable docker

add Kubernetes repository.

cat <<EOF > /etc/yum.repos.d/kubernetes.repo

then install kubelet, kubeadm and kubectl on all nodes and then reboot the servers.

yum install -y kubelet kubeadm kubectl --disableexcludes=kubernetes

once booted back lets start and enable the autostart of kubelet

systemctl start kubelet && systemctl enable kubelet

kubernetes and docker both need to be running under same cgroup, find out what cgroup docker is running under by running:

docker info | grep -i cgroup

now lets make sure kubernetes cgroup-driver is set to cgroupfs as well.

sed -i 's/cgroup-driver=systemd/cgroup-driver=cgroupfs/g' /etc/systemd/system/kubelet.service.d/10-kubeadm.conf

now reload the systemd and restart the kubelet service.

systemctl daemon-reload
systemctl restart kubelet

we need to make sure port 6443 & 10250 are open on the firewalld (default shipped with CentOS7). in my case I prefer to completely disable firewalld as these machines are not publicly available and only machines behind our proxy servers will be able to access them.

service firewalld stop
systemctl disable firewalld

lets create the cluster by running this command on the master.

kubeadm init --apiserver-advertise-address= --pod-network-cidr=

once done you should get a commend outputed to the screen which need to be run on the nodes to join the master in cluster. run it on each of the nodes. I’d say keep this in your notes for future where if you may have additional nodes.

  kubeadm join --token r5x6ce.bsaypyibs1m169y9 --discovery-token-ca-cert-hash sha256:xxxx

run the join command with your token on each node to get them to join the cluster.

thats all, you can confirm your nodes joined the master by running kubectl get nodes.

[root@kubemaster ~]# kubectl get nodes
kube1        Ready    <none>   4d18h   v1.13.1
kube2        Ready    <none>   4d18h   v1.13.1
kubemaster   Ready    master   4d18h   v1.13.1



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