Install Kubernetes Cluster on CentOS 7 with kubeadm

This guide will teach you how to deploy a minimum viable Kubernetes Cluster on CentOS 7 by using kubeadm tool. Kubeadm is a command line tool created to help users bootstrap a Kubernetes cluster that conforms to best practices. This tool supports cluster lifecycle management functions such as bootstrap tokens and cluster upgrades.

For Debian installation: Deploy Kubernetes Cluster on Debian 10 with Kubespray

For Rocky Linux 8: Install Kubernetes Cluster on Rocky Linux 8 with Kubeadm & CRI-O

The next sections will discuss in detail the process of deploying a minimal Kubernetes cluster on CentOS 7 servers. This installation is for a single control-plane cluster. We have other guides on deployment of highly available Kubernetes cluster with RKE and Kubespray.

The minimal server requirements for the servers used in the cluster are:

  • 2 GiB or more of RAM per machine–any less leaves little room for your apps.
  • At least 2 CPUs on the machine that you use as a control-plane node.
  • Full network connectivity among all machines in the cluster — Can be private or public

Since this setup is meant for development purposes, I have server with below details

Server Type Server Hostname Specs Master k8s-master01.computingpost.com 4GB Ram, 2vcpus Worker k8s-worker01.computingpost.com 4GB Ram, 2vcpus Worker k8s-worker02.computingpost.com 4GB Ram, 2vcpus

Login to all servers and update the OS.

sudo yum -y update && sudo systemctl reboot

Once the servers are rebooted, add Kubernetes repository for CentOS 7 to all the servers.

sudo tee /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

EOF

Then install required packages.

sudo yum clean all && sudo yum -y makecache

sudo yum -y install epel-release vim git curl wget kubelet kubeadm kubectl --disableexcludes=kubernetes

Confirm installation by checking the version of kubeadm and kubectl.

$ kubeadm  version

kubeadm version: &version.InfoMajor:"1", Minor:"22", GitVersion:"v1.22.2", GitCommit:"8b5a19147530eaac9476b0ab82980b4088bbc1b2", GitTreeState:"clean", BuildDate:"2021-09-15T21:37:34Z", GoVersion:"go1.16.8", Compiler:"gc", Platform:"linux/amd64"



$ kubectl version --client

Client Version: version.InfoMajor:"1", Minor:"22", GitVersion:"v1.22.2", GitCommit:"8b5a19147530eaac9476b0ab82980b4088bbc1b2", GitTreeState:"clean", BuildDate:"2021-09-15T21:38:50Z", GoVersion:"go1.16.8", Compiler:"gc", Platform:"linux/amd64"

If you have SELinux in enforcing mode, turn it off or use Permissive mode.

sudo setenforce 0

sudo sed -i 's/^SELINUX=.*/SELINUX=permissive/g' /etc/selinux/config

Turn off swap.

sudo sed -i '/ swap / s/^\(.*\)$/#\1/g' /etc/fstab

sudo swapoff -a

Configure sysctl.

sudo modprobe overlay

sudo modprobe br_netfilter



sudo tee /etc/sysctl.d/kubernetes.conf<net.bridge.bridge-nf-call-ip6tables = 1

net.bridge.bridge-nf-call-iptables = 1

net.ipv4.ip_forward = 1

EOF



sudo sysctl --system

To run containers in Pods, Kubernetes uses a container runtime. Supported container runtimes are:

  • Docker
  • CRI-O
  • Containerd

NOTE: You have to choose one runtime at a time.

For CRI-O below are the installation steps.

# Ensure you load modules

sudo modprobe overlay

sudo modprobe br_netfilter



# Set up required sysctl params

sudo tee /etc/sysctl.d/kubernetes.conf<net.bridge.bridge-nf-call-ip6tables = 1

net.bridge.bridge-nf-call-iptables = 1

net.ipv4.ip_forward = 1

EOF



# Reload sysctl

sudo sysctl --system



# Add CRI-O repo

OS=CentOS_7

VERSION=1.22

curl -L -o /etc/yum.repos.d/devel:kubic:libcontainers:stable.repo https://download.opensuse.org/repositories/devel:/kubic:/libcontainers:/stable/$OS/devel:kubic:libcontainers:stable.repo

curl -L -o /etc/yum.repos.d/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable:cri-o:$VERSION/$OS/devel:kubic:libcontainers:stable:cri-o:$VERSION.repo



# Install CRI-O

sudo yum remove docker-ce docker-ce-cli containerd.io

sudo yum install cri-o



# Update CRI-O Subnet

sudo sed -i 's/10.85.0.0/192.168.0.0/g' /etc/cni/net.d/100-crio-bridge.conf



# Start and enable Service

sudo systemctl daemon-reload

sudo systemctl start crio

sudo systemctl enable crio

When using Docker container engine run the commands below to install it:

# Install packages

sudo yum install -y yum-utils device-mapper-persistent-data lvm2

sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo

sudo yum install docker-ce docker-ce-cli containerd.io



# Create required directories

sudo mkdir /etc/docker

sudo mkdir -p /etc/systemd/system/docker.service.d



# Create daemon json config file

sudo tee /etc/docker/daemon.json <

"exec-opts": ["native.cgroupdriver=systemd"],

"log-driver": "json-file",

"log-opts":

"max-size": "100m"

,

"storage-driver": "overlay2",

"storage-opts": [

"overlay2.override_kernel_check=true"

]



EOF



# Start and enable Services

sudo systemctl daemon-reload

sudo systemctl restart docker

sudo systemctl enable docker

Below are the installation steps for Containerd.

# Configure persistent loading of modules

sudo tee /etc/modules-load.d/containerd.conf <overlay

br_netfilter

EOF



# Load at runtime

sudo modprobe overlay

sudo modprobe br_netfilter



# Ensure sysctl params are set

sudo tee /etc/sysctl.d/kubernetes.conf<net.bridge.bridge-nf-call-ip6tables = 1

net.bridge.bridge-nf-call-iptables = 1

net.ipv4.ip_forward = 1

EOF



# Reload configs

sudo sysctl --system



# Install required packages

sudo yum install -y yum-utils device-mapper-persistent-data lvm2



# Add Docker repo

sudo yum-config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo



# Install containerd

sudo yum update -y && yum install -y containerd.io



# Configure containerd and start service

sudo mkdir -p /etc/containerd

sudo containerd config default > /etc/containerd/config.toml



# restart containerd

sudo systemctl restart containerd

sudo systemctl enable containerd

To use the systemd cgroup driver, set plugins.cri.systemd_cgroup = true in /etc/containerd/config.toml. When using kubeadm, manually configure the cgroup driver for kubelet

I recommend you disable firewalld on your nodes:

sudo systemctl disable --now firewalld

If you have an active firewalld service there are a number of ports to be enabled.

Master Server ports:

sudo firewall-cmd --add-port=6443,2379-2380,10250,10251,10252,5473,179,5473/tcp --permanent

sudo firewall-cmd --add-port=4789,8285,8472/udp --permanent

sudo firewall-cmd --reload

Worker Node ports:

sudo firewall-cmd --add-port=10250,30000-32767,5473,179,5473/tcp --permanent

sudo firewall-cmd --add-port=4789,8285,8472/udp --permanent

sudo firewall-cmd --reload

Login to the server to be used as master and make sure that the br_netfilter module is loaded:

$ lsmod | grep br_netfilter

br_netfilter 22256 0

bridge 151336 2 br_netfilter,ebtable_broute

Enable kubelet service.

sudo systemctl enable kubelet

We now want to initialize the machine that will run the control plane components which includes etcd (the cluster database) and the API Server.

Pull container images:

$ sudo kubeadm config images pull

[config/images] Pulled k8s.gcr.io/kube-apiserver:v1.22.2

[config/images] Pulled k8s.gcr.io/kube-controller-manager:v1.22.2

[config/images] Pulled k8s.gcr.io/kube-scheduler:v1.22.2

[config/images] Pulled k8s.gcr.io/kube-proxy:v1.22.2

[config/images] Pulled k8s.gcr.io/pause:3.5

[config/images] Pulled k8s.gcr.io/etcd:3.5.0-0

[config/images] Pulled k8s.gcr.io/coredns/coredns:v1.8.4

These are the basic kubeadm init options that are used to bootstrap cluster.

--control-plane-endpoint :  set the shared endpoint for all control-plane nodes. Can be DNS/IP

--pod-network-cidr : Used to set a Pod network add-on CIDR

--cri-socket : Use if have more than one container runtime to set runtime socket path

--apiserver-advertise-address : Set advertise address for this particular control-plane node's API server

Set cluster endpoint DNS name or add record to /etc/hosts file.

$ sudo vim /etc/hosts

172.29.20.5 k8s-cluster.computingpost.com

Create cluster:

sudo kubeadm init \

--pod-network-cidr=192.168.0.0/16 \

--upload-certs \

--control-plane-endpoint=k8s-cluster.computingpost.com

Note: If 192.168.0.0/16 is already in use within your network you must select a different pod network CIDR, replacing 192.168.0.0/16 in the above command.

Container runtime sockets:

Runtime Path to Unix domain socket Docker /var/run/docker.sock containerd /run/containerd/containerd.sock CRI-O /var/run/crio/crio.sock

You can optionally pass Socket file for runtime and advertise address depending on your setup.

sudo kubeadm init \

--pod-network-cidr=192.168.0.0/16 \

--cri-socket /var/run/crio/crio.sock \

--upload-certs \

--control-plane-endpoint=k8s-cluster.computingpost.com

Here is the output of my initialization command.

....

[init] Using Kubernetes version: v1.22.2

[preflight] Running pre-flight checks

[WARNING Firewalld]: firewalld is active, please ensure ports [6443 10250] are open or your cluster may not function correctly

[preflight] Pulling images required for setting up a Kubernetes cluster

[preflight] This might take a minute or two, depending on the speed of your internet connection

[preflight] You can also perform this action in beforehand using 'kubeadm config images pull'

[kubelet-start] Writing kubelet environment file with flags to file "/var/lib/kubelet/kubeadm-flags.env"

[kubelet-start] Writing kubelet configuration to file "/var/lib/kubelet/config.yaml"

[kubelet-start] Starting the kubelet

[certs] Using certificateDir folder "/etc/kubernetes/pki"

[certs] Using existing ca certificate authority

[certs] Using existing apiserver certificate and key on disk

[certs] Using existing apiserver-kubelet-client certificate and key on disk

[certs] Using existing front-proxy-ca certificate authority

[certs] Using existing front-proxy-client certificate and key on disk

[certs] Using existing etcd/ca certificate authority

[certs] Using existing etcd/server certificate and key on disk

[certs] Using existing etcd/peer certificate and key on disk

[certs] Using existing etcd/healthcheck-client certificate and key on disk

[certs] Using existing apiserver-etcd-client certificate and key on disk

[certs] Using the existing "sa" key

[kubeconfig] Using kubeconfig folder "/etc/kubernetes"

[kubeconfig] Using existing kubeconfig file: "/etc/kubernetes/admin.conf"

[kubeconfig] Using existing kubeconfig file: "/etc/kubernetes/kubelet.conf"

[kubeconfig] Using existing kubeconfig file: "/etc/kubernetes/controller-manager.conf"

[kubeconfig] Using existing kubeconfig file: "/etc/kubernetes/scheduler.conf"

[control-plane] Using manifest folder "/etc/kubernetes/manifests"

[control-plane] Creating static Pod manifest for "kube-apiserver"

[control-plane] Creating static Pod manifest for "kube-controller-manager"

W0611 22:34:23.276374 4726 manifests.go:225] the default kube-apiserver authorization-mode is "Node,RBAC"; using "Node,RBAC"

[control-plane] Creating static Pod manifest for "kube-scheduler"

W0611 22:34:23.278380 4726 manifests.go:225] the default kube-apiserver authorization-mode is "Node,RBAC"; using "Node,RBAC"

[etcd] Creating static Pod manifest for local etcd in "/etc/kubernetes/manifests"

[wait-control-plane] Waiting for the kubelet to boot up the control plane as static Pods from directory "/etc/kubernetes/manifests". This can take up to 4m0s

[apiclient] All control plane components are healthy after 8.008181 seconds

[upload-config] Storing the configuration used in ConfigMap "kubeadm-config" in the "kube-system" Namespace

[kubelet] Creating a ConfigMap "kubelet-config-1.22" in namespace kube-system with the configuration for the kubelets in the cluster

[upload-certs] Skipping phase. Please see --upload-certs

[mark-control-plane] Marking the node k8s-master01.computingpost.com as control-plane by adding the label "node-role.kubernetes.io/master=''"

[mark-control-plane] Marking the node k8s-master01.computingpost.com as control-plane by adding the taints [node-role.kubernetes.io/master:NoSchedule]

[bootstrap-token] Using token: zoy8cq.6v349sx9ass8dzyj

[bootstrap-token] Configuring bootstrap tokens, cluster-info ConfigMap, RBAC Roles

[bootstrap-token] configured RBAC rules to allow Node Bootstrap tokens to get nodes

[bootstrap-token] configured RBAC rules to allow Node Bootstrap tokens to post CSRs in order for nodes to get long term certificate credentials

[bootstrap-token] configured RBAC rules to allow the csrapprover controller automatically approve CSRs from a Node Bootstrap Token

[bootstrap-token] configured RBAC rules to allow certificate rotation for all node client certificates in the cluster

[bootstrap-token] Creating the "cluster-info" ConfigMap in the "kube-public" namespace

[kubelet-finalize] Updating "/etc/kubernetes/kubelet.conf" to point to a rotatable kubelet client certificate and key

[addons] Applied essential addon: CoreDNS

[addons] Applied essential addon: kube-proxy



Your Kubernetes control-plane has initialized successfully!



To start using your cluster, you need to run the following as a regular user:



mkdir -p $HOME/.kube

sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config

sudo chown $(id -u):$(id -g) $HOME/.kube/config



You should now deploy a pod network to the cluster.

Run "kubectl apply -f [podnetwork].yaml" with one of the options listed at:

https://kubernetes.io/docs/concepts/cluster-administration/addons/



You can now join any number of control-plane nodes by copying certificate authorities

and service account keys on each node and then running the following as root:



kubeadm join k8s-cluster.computingpost.com:6443 --token zoy8cq.6v349sx9ass8dzyj \

--discovery-token-ca-cert-hash sha256:14a6e33ca8dc9998f984150bc8780ddf0c3ff9cf6a3848f49825e53ef1374e24 \

--control-plane



Then you can join any number of worker nodes by running the following on each as root:



kubeadm join k8s-cluster.computingpost.com:6443 --token zoy8cq.6v349sx9ass8dzyj \

--discovery-token-ca-cert-hash sha256:14a6e33ca8dc9998f984150bc8780ddf0c3ff9cf6a3848f49825e53ef1374e24

Configure kubectl using commands in the output:

mkdir -p $HOME/.kube

sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config

sudo chown $(id -u):$(id -g) $HOME/.kube/config

Check cluster status:

$ kubectl cluster-info

Kubernetes master is running at https://k8s-cluster.computingpost.com:6443

KubeDNS is running at https://k8s-cluster.computingpost.com:6443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy



To further debug and diagnose cluster problems, use 'kubectl cluster-info dump'.

Additional Master nodes can be added using the command in installation output:

kubeadm join k8s-cluster.computingpost.com:6443 \

--token zoy8cq.6v349sx9ass8dzyj \

--discovery-token-ca-cert-hash sha256:14a6e33ca8dc9998f984150bc8780ddf0c3ff9cf6a3848f49825e53ef1374e24 \

--control-plane

In this guide we’ll use Calico. You can choose any other supported network plugins.

kubectl create -f https://docs.projectcalico.org/manifests/tigera-operator.yaml 

kubectl create -f https://docs.projectcalico.org/manifests/custom-resources.yaml

You should see the following output.

customresourcedefinition.apiextensions.k8s.io/bgpconfigurations.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/bgppeers.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/blockaffinities.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/clusterinformations.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/felixconfigurations.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/globalnetworkpolicies.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/globalnetworksets.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/hostendpoints.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/ipamblocks.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/ipamconfigs.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/ipamhandles.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/ippools.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/kubecontrollersconfigurations.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/networkpolicies.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/networksets.crd.projectcalico.org created

customresourcedefinition.apiextensions.k8s.io/apiservers.operator.tigera.io created

customresourcedefinition.apiextensions.k8s.io/imagesets.operator.tigera.io created

customresourcedefinition.apiextensions.k8s.io/installations.operator.tigera.io created

customresourcedefinition.apiextensions.k8s.io/tigerastatuses.operator.tigera.io created

namespace/tigera-operator created

Warning: policy/v1beta1 PodSecurityPolicy is deprecated in v1.21+, unavailable in v1.25+

podsecuritypolicy.policy/tigera-operator created

serviceaccount/tigera-operator created

clusterrole.rbac.authorization.k8s.io/tigera-operator created

clusterrolebinding.rbac.authorization.k8s.io/tigera-operator created

deployment.apps/tigera-operator created

.....

installation.operator.tigera.io/default created

apiserver.operator.tigera.io/default created

Confirm that all of the pods are running:

$ kubectl get pods --all-namespaces

NAMESPACE NAME READY STATUS RESTARTS AGE

calico-system calico-kube-controllers-767ddd5576-t55pr 1/1 Running 0 37s

calico-system calico-node-nkhqf 1/1 Running 0 37s

calico-system calico-typha-955b599b6-2w426 1/1 Running 0 37s

kube-system coredns-78fcd69978-v4hff 1/1 Running 0 2m12s

kube-system coredns-78fcd69978-x489k 1/1 Running 0 2m12s

kube-system etcd-centos.hirebestengineers.com 1/1 Running 0 2m25s

kube-system kube-apiserver-centos.hirebestengineers.com 1/1 Running 0 2m25s

kube-system kube-controller-manager-centos.hirebestengineers.com 1/1 Running 0 2m25s

kube-system kube-proxy-6bvmp 1/1 Running 0 2m12s

kube-system kube-scheduler-centos.hirebestengineers.com 1/1 Running 0 2m25s

tigera-operator tigera-operator-59f4845b57-s9tfz 1/1 Running 0 46s

Confirm master node is ready:

$ kubectl get nodes -o wide

NAME STATUS ROLES AGE VERSION INTERNAL-IP EXTERNAL-IP OS-IMAGE KERNEL-VERSION CONTAINER-RUNTIME

centos.hirebestengineers.com Ready control-plane,master 2m58s v1.22.2 142.93.14.175 CentOS Linux 7 (Core) 3.10.0-1160.42.2.el7.x86_64 docker://20.10.9

With the control plane ready you can add worker nodes to the cluster for running scheduled workloads.

If endpoint address is not in DNS, add record to /etc/hosts.

$ sudo vim /etc/hosts

172.29.20.5 k8s-cluster.computingpost.com

The join command that was given is used to add a worker node to the cluster.

kubeadm join k8s-cluster.computingpost.com:6443 \

--token zoy8cq.6v349sx9ass8dzyj \

--discovery-token-ca-cert-hash sha256:14a6e33ca8dc9998f984150bc8780ddf0c3ff9cf6a3848f49825e53ef1374e24

Output:

[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-1.22" 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 below command on the control-plane to see if the node joined the cluster.

$ kubectl get nodes

NAME STATUS ROLES AGE VERSION

k8s-master01.computingpost.com Ready master 18m v1.22.2

k8s-worker01.computingpost.com Ready 98s v1.22.2

If the join token is expired, refer to our guide on how to join worker nodes.

For single node cluster check out our guide on how to run pods on control plane nodes:

We need to validate that our cluster is working by deploying an application.

kubectl apply -f https://k8s.io/examples/pods/commands.yaml

Check to see if pod started

$ kubectl get pods

NAME READY STATUS RESTARTS AGE

command-demo 0/1 Completed 0 40s

Kubernetes dashboard can be used to deploy containerized applications to a Kubernetes cluster, troubleshoot your containerized application, and manage the cluster resources.

Refer to our guide for installation: How To Install Kubernetes Dashboard with NodePort

If Nginx is your preferred Ingress controller for Kubernetes workloads, you can use our guide in the following link for the installation process:

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