Kubernetes is an open-source platform for managing containerized applications. It allows you to manage, scale, and automatically deploy your containerized applications in the clustered environment. Kubernetes is developed by Google.
With Kubernetes, you can orchestrate containers across multiple hosts, scale the containerized applications with all resources on the fly, and have a centralized container management environment.
In this article, I will show you step-by-step how to install and configure Kubernetes on CentOS version 8. We will be using 1 server ‘KubeMaster‘ as the Kubernetes Master Node, and 2 servers as Kubernetes workers, ‘minion-1‘ and ‘minion-2‘.
- KubeMaster: 192.168.4.130
- minion-1 : 192.168.4.131
- minion-2 : 192.168.4.132
Master Node – This machine generally acts as the control plane and runs the cluster database and the API server (which the kubectl CLI communicates with).
Our 3-node Kubernetes Cluster will look something like this:
Prepare Hostname, Firewall, swap, and SELinux
On your CentOS 8, Master-Node set the system hostname and update DNS in your /etc/hosts file.
[root@KubeMaster ~]# cat <<EOF>> /etc/hosts
> 192.168.4.130 KubeMaster
> 192.168.4.131 minion-1
> 192.168.4.132 minion-2
> EOFNext, disable Selinux(On all three machines), as this is required to allow containers to access the host filesystem, which is needed by pod networks and other services.
[root@KubeMaster ~]# setenforce 0
setenforce: SELinux is disabledTo completely disable it, use the below command and reboot
[root@KubeMaster ~]# sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinux Configure the firewall rules on the ports.
#firewall-cmd --zone=public --permanent --add-port={2379,2380,6443,10250,1021,10252,10255}/tcp
#firewall-cmd --reload Next, disable the swap (on all three machines) with the following command:
[root@KubeMaster ~]# swapoff -a We must also ensure that swap isn’t re-enabled during a reboot on each server. Open up the /etc/fstab and comment out the swap entry like this:
[root@KubeMaster ~]# cat /etc/fstab | grep swap
#/dev/mapper/cs_controller-swap swap swap defaults 0 0Enable br_netfilter
For our next trick, we’ll be enabling the br_netfilter kernel module on all three servers. This is done with the following commands:
[root@KubeMaster ~]# modprobe br_netfilter
[root@KubeMaster ~]# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptablesInstall Docker:
1. Add the repository for the docker installation package.
[root@KubeMaster ~]# dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repo
Adding repo from: https://download.docker.com/linux/centos/docker-ce.repo 2. Install container.io which is not yet provided by the package manager before installing docker.
[root@KubeMaster ~]# dnf install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.6-3.3.el7.x86_64.rpm
Last metadata expiration check: 0:03:03 ago on Mon 08 Jun 2020 05:38:24 PM IST.
containerd.io-1.2.6-3.3.el7.x86_64.rpm 5.3 MB/s | 26 MB 00:04
Dependencies resolved.
===============================================================================================================================================================
Package Architecture Version Repository Size
===============================================================================================================================================================
Installing:
containerd.io x86_64 1.2.6-3.3.el7 @commandline 26 M
Installing dependencies:
container-selinux noarch 2:2.124.0-1.module_el8.1.0+298+41f9343a AppStream 47 k
Transaction Summary
===============================================================================================================================================================
Install 2 Packages3. Then install Docker from the repositories.
[root@KubeMaster ~]# dnf install docker-ce
Last metadata expiration check: 0:39:00 ago on Mon 08 Jun 2020 05:38:24 PM IST.
Dependencies resolved.
===============================================================================================================================================================
Package Architecture Version Repository Size
===============================================================================================================================================================
Installing:
docker-ce x86_64 3:19.03.11-3.el7 docker-ce-stable 24 M
Installing dependencies:
docker-ce-cli x86_64 1:19.03.11-3.el7 docker-ce-stable 38 M
libcgroup x86_64 0.41-19.el8 BaseOS 70 k
Transaction Summary
===============================================================================================================================================================
Install 3 Packages4. Start & enable the docker services.
[root@KubeMaster ~]# systemctl start docker.service
[root@KubeMaster ~]# systemctl enable docker.service
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service → /usr/lib/systemd/system/docker.service. 5. See the docker version.
[root@KubeMaster ~]# docker version
Client: Docker Engine - Community
Version: 19.03.11
API version: 1.40
Go version: go1.13.10
Git commit: 42e35e61f3
Built: Mon Jun 1 09:13:48 2020
OS/Arch: linux/amd64
Experimental: false
Server: Docker Engine - Community
Engine:
Version: 19.03.11
API version: 1.40 (minimum version 1.12)
Go version: go1.13.10
Git commit: 42e35e61f3
Built: Mon Jun 1 09:12:26 2020
OS/Arch: linux/amd64
Experimental: false
containerd:
Version: 1.2.6
GitCommit: 894b81a4b802e4eb2a91d1ce216b8817763c29fb
runc:
Version: 1.0.0-rc8
GitCommit: 425e105d5a03fabd737a126ad93d62a9eeede87f
docker-init:
Version: 0.18.0
GitCommit: fec36836. List what is inside the docker images.
[root@KubeMaster ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
weaveworks/weave-npc 2.6.4 78ae9e32f34e 9 days ago 36.8MB
weaveworks/weave-kube 2.6.4 32950afead86 9 days ago 123MB
k8s.gcr.io/kube-proxy v1.18.3 3439b7546f29 2 weeks ago 117MB
k8s.gcr.io/kube-controller-manager v1.18.3 da26705ccb4b 2 weeks ago 162MB
k8s.gcr.io/kube-apiserver v1.18.3 7e28efa976bd 2 weeks ago 173MB
k8s.gcr.io/kube-scheduler v1.18.3 76216c34ed0c 2 weeks ago 95.3MB
k8s.gcr.io/pause 3.2 80d28bedfe5d 3 months ago 683kB
k8s.gcr.io/coredns 1.6.7 67da37a9a360 4 months ago 43.8MB
k8s.gcr.io/etcd 3.4.3-0 303ce5db0e90 7 months ago 288MBNow that Docker is ready to go, continue below to install Kubernetes itself.
Installing Kubernetes:
Add the Kubernetes repository to your package manager by creating the following file
[root@KubeMaster ~]# cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOFkubeadm is a tool built to provide “kubeadm init” and “kubeadm join” as best-practice “fast paths” for creating Kubernetes clusters.
kubeadm performs the actions necessary to get a minimum viable cluster up and running. By design, it cares only about bootstrapping, not about provisioning machines. Likewise, installing various nice-to-have addons, like the Kubernetes Dashboard, monitoring solutions, and cloud-specific add-ons is not in scope.
[root@KubeMaster ~]# dnf install kubeadm -y
Last metadata expiration check: 0:00:56 ago on Mon 08 Jun 2020 06:50:40 PM IST.
Dependencies resolved.
===============================================================================================================================================================
Package Architecture Version Repository Size
===============================================================================================================================================================
Installing:
kubeadm x86_64 1.18.3-0 kubernetes 8.8 M
Installing dependencies:
conntrack-tools x86_64 1.4.4-10.el8 Stream-BaseOS 204 k
cri-tools x86_64 1.13.0-0 kubernetes 5.1 M
kubectl x86_64 1.18.3-0 kubernetes 9.5 M
kubelet x86_64 1.18.3-0 kubernetes 21 M
kubernetes-cni x86_64 0.7.5-0 kubernetes 10 M
libnetfilter_cthelper x86_64 1.0.0-15.el8 Stream-BaseOS 24 k
libnetfilter_cttimeout x86_64 1.0.0-11.el8 BaseOS 24 k
libnetfilter_queue x86_64 1.0.2-11.el8 BaseOS 30 k
socat x86_64 1.7.3.3-2.el8 Stream-AppStream 302 k
Transaction Summary
===============================================================================================================================================================
Install 10 PackagesStart the Kubernetes services and enable them to run at startup.
[root@KubeMaster ~]# systemctl start kubelet.service
[root@KubeMaster ~]# systemctl enable kubelet.serviceSet up the Kubernetes Control Plane
After installing the Kubernetes-related tooling on all your machines, you are ready to set up the Kubernetes control plane on the master node. The control plane is responsible for allocating resources to your cluster, maintaining the health of your cluster, and ensuring that it meets the minimum requirements you designate for the cluster.
The primary components of the control plane are the kube-apiserver, kube-controller-manager, kube-scheduler, and etcd. You can easily initialize the Kubernetes master node with all the necessary control plane components using kubeadm.
[root@KubeMaster ~]# kubeadm init
Next, copy the following command and store it somewhere, as we required to run this command on the worker nodes later.
kubeadm join 192.168.4.130:6443 --token pknv09.7zu6jfcqpjp1r9cf
--discovery-token-ca-cert-hash sha256:98685c3b9ea0611c28c17889784e8fe0d058996de36138e761f932b2a08a90db Make the following directory and configuration files.
[root@KubeMaster ~]# mkdir -p $HOME/.kube
[root@KubeMaster ~]# sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config
[root@KubeMaster ~]# sudo chown $(id -u):$(id -g) $HOME/.kube/configNow confirm that the kubectl command is activated.
[root@KubeMaster ~]# kubectl get nodes
NAME STATUS ROLES AGE VERSION
kubemaster NotReady master 33m v1.18.3At this moment, you will see the status of the master-node is ‘NotReady’. This is because we are yet to deploy the pod network to the cluster.
The pod Network is the overlay network for the cluster, that is deployed on top of the present node network. It is designed to allow connectivity across the pod.
Setting up POD Networking:
Deploying the network cluster is a highly flexible process depending on your needs and there are many options available. Since we want to keep our installation as simple as possible, we will use Weavenet plugin which does not require any configuration or extra code and it provides one IP address per pod which is great for us.
[root@KubeMaster ~]# export kubever=$(kubectl version | base64 | tr -d 'n')
[root@KubeMaster ~]# kubectl apply -f "https://cloud.weave.works/k8s/net?k8s-version=$kubever"
serviceaccount/weave-net created
clusterrole.rbac.authorization.k8s.io/weave-net created
clusterrolebinding.rbac.authorization.k8s.io/weave-net created
role.rbac.authorization.k8s.io/weave-net created
rolebinding.rbac.authorization.k8s.io/weave-net created
daemonset.apps/weave-net createdNow if you check the status of your master-node, it should be ‘Ready‘.
[root@KubeMaster ~]# kubectl get nodes
NAME STATUS ROLES AGE VERSION
kubemaster Ready master 41m v1.18.3Next, we add the worker nodes to the cluster.
Adding Worker Nodes to Kubernetes Cluster:
Prepare Hostname, Firewall, swap and SELinux
First set the hostname on your worker-node-1 and worker-node-2 and then add the host entries to the /etc/hosts file.
# cat <<EOF>> /etc/hosts
192.168.4.130 KubeMaster
192.168.4.131 minion-1
192.168.4.132 minion-2
EOFNext, disable SElinux and update your firewall rules.
# setenforce 0
#sed -i --follow-symlinks 's/SELINUX=enforcing/SELINUX=disabled/g' /etc/sysconfig/selinuxConfigure the firewall rules on the ports.
#firewall-cmd --zone=public --permanent --add-port={6783,10250,10255,30000-32767}/tcp
#firewall-cmd --reloadDisable swap (on all three machines) with the following command:
#swapoff -aWe must also ensure that swap isn’t re-enabled during a reboot on each server. Open up the /etc/fstab and comment out the swap entry
# modprobe br_netfilter
# echo '1' > /proc/sys/net/bridge/bridge-nf-call-iptables Setup Docker-CE and Kubernetes Repo
Add the Docker repository first using DNF config-manager.
# dnf config-manager --add-repo=https://download.docker.com/linux/centos/docker-ce.repoNext, add the containerd.io package.
# dnf install https://download.docker.com/linux/centos/7/x86_64/stable/Packages/containerd.io-1.2.6-3.3.el7.x86_64.rpmInstall the latest version of docker-ce
# dnf install docker-ce -yEnable and start the docker service.
# systemctl enable docker
# systemctl start dockerYou will need to add Kubernetes repositories manually as they do not come pre-installed on CentOS8.
# cat <<EOF > /etc/yum.repos.d/kubernetes.repo
[kubernetes]
name=Kubernetes
baseurl=https://packages.cloud.google.com/yum/repos/kubernetes-el7-x86_64
enabled=1
gpgcheck=1
repo_gpgcheck=1
gpgkey=https://packages.cloud.google.com/yum/doc/yum-key.gpg https://packages.cloud.google.com/yum/doc/rpm-package-key.gpg
EOFInstall Kubernetes
Install kubernetes with “kubeadm“
# dnf install kubeadm -yStart and enable the service.
# systemctl enable kubelet
# systemctl start kubeletJoin the Worker Node to the Kubernetes Cluster
We now require the token that kubeadm init generated, to join the cluster. You can copy and paste it to your node-1 and node-2 if you had copied it somewhere.
[root@minion-1 ~]# kubeadm join 192.168.4.130:6443 --token pknv09.7zu6jfcqpjp1r9cf --discovery-token-ca-cert-hash sha256:98685c3b9ea0611c28c17889784e8fe0d058996de36138e761f932b2a08a90db
W0609 06:51:23.718580 2433 join.go:346] [preflight] WARNING: JoinControlPane.controlPlane settings will be ignored when control-plane flag is not set.
[preflight] Running pre-flight checks
[WARNING IsDockerSystemdCheck]: detected "cgroupfs" as the Docker cgroup driver. The recommended driver is "systemd". Please follow the guide at https://kubernetes.io/docs/setup/cri/
[WARNING FileExisting-tc]: tc not found in system path
[preflight] Reading configuration from the cluster...
[preflight] FYI: You can look at this config file with 'kubectl -n kube-system get cm kubeadm-config -oyaml'
[kubelet-start] Downloading configuration for the kubelet from the "kubelet-config-1.18" ConfigMap in the kube-system namespace
[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Starting the kubelet
[kubelet-start] Waiting for the kubelet to perform the TLS Bootstrap...
This node has joined the cluster:
* Certificate signing request was sent to apiserver and a response was received.
* The Kubelet was informed of the new secure connection details.
Run 'kubectl get nodes' on the control-plane to see this node join the cluster.See if the Worker nodes successfully joined.
Go back to the Master node and issue the following command.
# kubectl get nodes
List all Container images in all namespaces
Finished.
In case anything goes wrong, you can always repeat the process.
Run this on Master and workers:
# kubeadm reset && rm -rf /etc/cni/net.d Thank you…!!
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