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CentOS

• Prerequisites
• Starting a cluster
• Support Level

Prerequisites

You need two machines with CentOS installed on them.

Starting a cluster

This is a getting started guide for CentOS. It is a manual configuration so you understand all the underlying packages / services / ports, etc…

This guide will only get ONE node working. Multiple nodes requires a functional networking configuration done outside of kubernetes. Although the additional Kubernetes configuration requirements should be obvious.

The Kubernetes package provides a few services: kube-apiserver, kube-scheduler, kube-controller-manager, kubelet, kube-proxy. These services are managed by systemd and the configuration resides in a central location: /etc/kubernetes. We will break the services up between the hosts. The first host, centos-master, will be the Kubernetes master. This host will run the kube-apiserver, kube-controller-manager, and kube-scheduler. In addition, the master will also run etcd. The remaining host, centos-minion will be the node and run kubelet, proxy, cadvisor and docker.

System Information:

Hosts:

centos-master = 192.168.121.9
centos-minion = 192.168.121.65

Prepare the hosts:

• Create a virt7-docker-common-release repo on all hosts - centos-{master,minion} with following information.

[virt7-docker-common-release]
name=virt7-docker-common-release
baseurl=http://cbs.centos.org/repos/virt7-docker-common-release/x86_64/os/
gpgcheck=0

• Install Kubernetes on all hosts - centos-{master,minion}. This will also pull in etcd, docker, and cadvisor.

yum -y install --enablerepo=virt7-docker-common-release kubernetes

• Add master and node to /etc/hosts on all machines (not needed if hostnames already in DNS)

echo "192.168.121.9	centos-master
192.168.121.65	centos-minion" >> /etc/hosts

• Edit /etc/kubernetes/config which will be the same on all hosts to contain:

# Comma separated list of nodes in the etcd cluster
KUBE_ETCD_SERVERS="--etcd-servers=http://centos-master:2379"

# logging to stderr means we get it in the systemd journal
KUBE_LOGTOSTDERR="--logtostderr=true"

# journal message level, 0 is debug
KUBE_LOG_LEVEL="--v=0"

# Should this cluster be allowed to run privileged docker containers
KUBE_ALLOW_PRIV="--allow-privileged=false"

• Disable the firewall on both the master and node, as docker does not play well with other firewall rule managers

systemctl disable iptables-services firewalld
systemctl stop iptables-services firewalld

Configure the Kubernetes services on the master.

• Edit /etc/kubernetes/apiserver to appear as such:

# The address on the local server to listen to.
KUBE_API_ADDRESS="--address=0.0.0.0"

# The port on the local server to listen on.
KUBE_API_PORT="--port=8080"

# How the replication controller and scheduler find the kube-apiserver
KUBE_MASTER="--master=http://centos-master:8080"

# Port kubelets listen on
KUBELET_PORT="--kubelet-port=10250"

# Address range to use for services
KUBE_SERVICE_ADDRESSES="--service-cluster-ip-range=10.254.0.0/16"

# Add your own!
KUBE_API_ARGS=""

• Start the appropriate services on master:

for SERVICES in etcd kube-apiserver kube-controller-manager kube-scheduler; do 
	systemctl restart $SERVICES
	systemctl enable $SERVICES
	systemctl status $SERVICES 
done

Configure the Kubernetes services on the node.

We need to configure the kubelet and start the kubelet and proxy

• Edit /etc/kubernetes/kubelet to appear as such:

# The address for the info server to serve on
KUBELET_ADDRESS="--address=0.0.0.0"

# The port for the info server to serve on
KUBELET_PORT="--port=10250"

# You may leave this blank to use the actual hostname
KUBELET_HOSTNAME="--hostname-override=centos-minion"

# Location of the api-server
KUBELET_API_SERVER="--api-servers=http://centos-master:8080"

# Add your own!
KUBELET_ARGS=""

• Start the appropriate services on node (centos-minion).

for SERVICES in kube-proxy kubelet docker; do 
    systemctl restart $SERVICES
    systemctl enable $SERVICES
    systemctl status $SERVICES 
done

You should be finished!

• Check to make sure the cluster can see the node (on centos-master)

$ kubectl get nodes
NAME                   LABELS            STATUS
centos-minion          <none>            Ready

The cluster should be running! Launch a test pod.

You should have a functional cluster, check out 101!

Support Level

For support level information on all solutions, see the Table of solutions chart.