kubernetes centos 7

By | October 29, 2016

Prerequisites

To configure Kubernetes with CentOS, you’ll need a machine to act as a master, and one or more CentOS 7 hosts to act as cluster nodes.
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…
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 hosts, centos-minion-n will be the nodes and run kubelet, proxy, cadvisor and docker.
All of then run flanneld as networking overlay.
System Information:
Hosts:
Please replace host IP with your environment.
centos-master = 192.168.121.9
centos-minion-1 = 192.168.121.65
centos-minion-2 = 192.168.121.66
centos-minion-3 = 192.168.121.67
Prepare the hosts:
Create a /etc/yum.repos.d/virt7-docker-common-release.repo on all hosts – centos-{master,minion-n} 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, etcd and flannel on all hosts – centos-{master,minion-n}. This will also pull in docker and cadvisor.
yum -y install –enablerepo=virt7-docker-common-release kubernetes etcd flannel
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-1
192.168.121.66 centos-minion-2
192.168.121.67 centos-minion-3″ >> /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”

# How the replication controller and scheduler find the kube-apiserver
KUBE_MASTER=”–master=http://centos-master:8080″
Disable the firewall on the master and all the nodes, 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/etcd/etcd.conf to appear as such:
# [member]
ETCD_NAME=default
ETCD_DATA_DIR=”/var/lib/etcd/default.etcd”
ETCD_LISTEN_CLIENT_URLS=”http://0.0.0.0:2379″

#[cluster]
ETCD_ADVERTISE_CLIENT_URLS=”http://0.0.0.0:2379″
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″

# 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=””
Configure ETCD to hold the network overlay configuration on master: Warning This network must be unused in your network infrastructure! 172.30.0.0/16 is free in our network.
$ etcdctl mkdir /kube-centos/network
$ etcdctl mk /kube-centos/network/config “{ \”Network\”: \”172.30.0.0/16\”, \”SubnetLen\”: 24, \”Backend\”: { \”Type\”: \”vxlan\” } }”
Configure flannel to overlay Docker network in /etc/sysconfig/flanneld on the master (also in the nodes as we’ll see):
# etcd url location. Point this to the server where etcd runs
FLANNEL_ETCD=”http://centos-master:2379″

# etcd config key. This is the configuration key that flannel queries
# For address range assignment
FLANNEL_ETCD_KEY=”/kube-centos/network”

# Any additional options that you want to pass
FLANNEL_OPTIONS=””
Start the appropriate services on master:
for SERVICES in etcd kube-apiserver kube-controller-manager kube-scheduler flanneld; do
systemctl restart $SERVICES
systemctl enable $SERVICES
systemctl status $SERVICES
done
Configure the Kubernetes services on the nodes.
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-n” # Check the node number!

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

# Add your own!
KUBELET_ARGS=””
Configure flannel to overlay Docker network in /etc/sysconfig/flanneld (in all the nodes)
# etcd url location. Point this to the server where etcd runs
FLANNEL_ETCD=”http://centos-master:2379″

# etcd config key. This is the configuration key that flannel queries
# For address range assignment
FLANNEL_ETCD_KEY=”/kube-centos/network”

# Any additional options that you want to pass
FLANNEL_OPTIONS=””
Start the appropriate services on node (centos-minion-n).
for SERVICES in kube-proxy kubelet flanneld docker; do
systemctl restart $SERVICES
systemctl enable $SERVICES
systemctl status $SERVICES
done
Configure kubectl
kubectl config set-cluster default-cluster –server=http://centos-master:8080
kubectl config set-context default-context –cluster=default-cluster –user=default-admin
kubectl config use-context default-context
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-1 Ready
centos-minion-2 Ready
centos-minion-3 Ready
The cluster should be running! Launch a test pod.
You should have a functional cluster, check out 101!

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