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Getting started on CentOS

Table of Contents

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 virt7-testing repo on all hosts - centos-{master,minion} with following information.
[virt7-testing]
name=virt7-testing
baseurl=http://cbs.centos.org/repos/virt7-testing/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-testing kubernetes
  • Note * Using etcd-0.4.6-7 (This is temporary update in documentation)

If you do not get etcd-0.4.6-7 installed with virt7-testing repo,

In the current virt7-testing repo, the etcd package is updated which causes service failure. To avoid this,

yum erase etcd

It will uninstall the current available etcd package

yum install http://cbs.centos.org/kojifiles/packages/etcd/0.4.6/7.el7.centos/x86_64/etcd-0.4.6-7.el7.centos.x86_64.rpm
yum -y install --enablerepo=virt7-testing 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:4001"

# 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"

# 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!

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