Kubernetes is a tool for orchestrating and managing Docker containers at scale on on-prem server or across hybrid cloud environments. Kubeadm is a tool provided with Kubernetes to help users install a production ready Kubernetes cluster with best practices enforcement. This tutorial will demonstrate how one can install a Kubernetes Cluster on Ubuntu 20.04 with kubeadm.

There are two server types used in deployment of Kubernetes clusters:

  • Master: A Kubernetes Master is where control API calls for the pods, replications controllers, services, nodes and other components of a Kubernetes cluster are executed.
  • Node: A Node is a system that provides the run-time environments for the containers. A set of container pods can span multiple nodes.

The minimum requirements for the viable setup are:

  • Memory: 2 GiB or more of RAM per machine
  • CPUs: At least 2 CPUs on the control plane machine.
  • Internet connectivity for pulling containers required (Private registry can also be used)
  • Full network connectivity between machines in the cluster – This is private or public

My Lab setup contain three servers. One control plane machine and two nodes to be used for running containerized workloads. You can add more nodes to suit your desired use case and load, for example using three control plane nodes for HA.

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

Step 1: Install Kubernetes Servers

Provision the servers to be used in the deployment of Kubernetes on Ubuntu 20.04. The setup process will vary depending on the virtualization or cloud environment you’re using.

Once the servers are ready, update them.

sudo apt update
sudo apt -y upgrade && sudo systemctl reboot

Step 2: Install kubelet, kubeadm and kubectl

Once the servers are rebooted, add Kubernetes repository for Ubuntu 20.04 to all the servers. 

sudo apt update
sudo apt -y install curl apt-transport-https
curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | sudo apt-key add -
echo "deb https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list

Then install required packages.

sudo apt update
sudo apt -y install vim git curl wget kubelet kubeadm kubectl
sudo apt-mark hold kubelet kubeadm kubectl

Confirm installation by checking the version of kubectl.

$ kubectl version --client && kubeadm version
Client Version: version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.3", GitCommit:"2e7996e3e2712684bc73f0dec0200d64eec7fe40", GitTreeState:"clean", BuildDate:"2020-05-20T12:52:00Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}
kubeadm version: &version.Info{Major:"1", Minor:"18", GitVersion:"v1.18.3", GitCommit:"2e7996e3e2712684bc73f0dec0200d64eec7fe40", GitTreeState:"clean", BuildDate:"2020-05-20T12:49:29Z", GoVersion:"go1.13.9", Compiler:"gc", Platform:"linux/amd64"}

Step 3: Disable Swap

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<<EOF
net.bridge.bridge-nf-call-ip6tables = 1
net.bridge.bridge-nf-call-iptables = 1
net.ipv4.ip_forward = 1
EOF

sudo sysctl --system

Step 4: Install Container runtime

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.

Installing Docker runtime:

# Add repo and Install packages
sudo apt update
sudo apt install -y curl gnupg2 software-properties-common apt-transport-https ca-certificates
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"
sudo apt update
sudo apt install -y containerd.io docker-ce docker-ce-cli

# Create required directories
sudo mkdir -p /etc/systemd/system/docker.service.d

# Create daemon json config file
sudo tee /etc/docker/daemon.json <<EOF
{
  "exec-opts": ["native.cgroupdriver=systemd"],
  "log-driver": "json-file",
  "log-opts": {
    "max-size": "100m"
  },
  "storage-driver": "overlay2"
}
EOF

# Start and enable Services
sudo systemctl daemon-reload 
sudo systemctl restart docker
sudo systemctl enable docker

Installing CRI-O:

# Ensure you load modules
sudo modprobe overlay
sudo modprobe br_netfilter

# Set up required sysctl params
sudo tee /etc/sysctl.d/kubernetes.conf< /etc/apt/sources.list.d/devel:kubic:libcontainers:stable.list"
wget -nv https://download.opensuse.org/repositories/devel:kubic:libcontainers:stable/x${NAME}_${VERSION_ID}/Release.key -O- | sudo apt-key add -
sudo apt update

# Install CRI-O
sudo apt install cri-o-1.17

# Start and enable Service
sudo systemctl daemon-reload
sudo systemctl start crio
sudo systemctl enable crio

Installing Containerd:

# Configure persistent loading of modules
sudo tee /etc/modules-load.d/containerd.conf <<EOF
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<<EOF
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 apt install -y curl gnupg2 software-properties-common apt-transport-https ca-certificates


# Add Docker repo
curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) stable"

# Install containerd
sudo apt update
sudo apt install -y containerd.io

# Configure containerd and start service
sudo mkdir -p /etc/containerd
sudo su -
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

Step 5: Initialize master node

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:v1.18.3
[config/images] Pulled k8s.gcr.io/kube-controller-manager:v1.18.3
[config/images] Pulled k8s.gcr.io/kube-scheduler:v1.18.3
[config/images] Pulled k8s.gcr.io/kube-proxy:v1.18.3
[config/images] Pulled k8s.gcr.io/pause:3.2
[config/images] Pulled k8s.gcr.io/etcd:3.4.3-0
[config/images] Pulled k8s.gcr.io/coredns:1.6.7

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.computingforgeeks.com

Create cluster:

sudo kubeadm init 
  --pod-network-cidr=192.168.0.0/16 
  --control-plane-endpoint=k8s-cluster.computingforgeeks.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.

Here is the output of my initialization command.

....
[init] Using Kubernetes version: v1.18.3
[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 "https://computingforgeeks.com/var/lib/kubelet/kubeadm-flags.env"
[kubelet-start] Writing kubelet configuration to file "https://computingforgeeks.com/var/lib/kubelet/config.yaml"
[kubelet-start] Starting the kubelet
[certs] Using certificateDir folder "https://computingforgeeks.com/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 "https://computingforgeeks.com/etc/kubernetes"
[kubeconfig] Using existing kubeconfig file: "https://computingforgeeks.com/etc/kubernetes/admin.conf"
[kubeconfig] Using existing kubeconfig file: "https://computingforgeeks.com/etc/kubernetes/kubelet.conf"
[kubeconfig] Using existing kubeconfig file: "https://computingforgeeks.com/etc/kubernetes/controller-manager.conf"
[kubeconfig] Using existing kubeconfig file: "https://computingforgeeks.com/etc/kubernetes/scheduler.conf"
[control-plane] Using manifest folder "https://computingforgeeks.com/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 "https://computingforgeeks.com/etc/kubernetes/manifests"
[wait-control-plane] Waiting for the kubelet to boot up the control plane as static Pods from directory "https://computingforgeeks.com/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-1.18" 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.computingforgeeks.com as control-plane by adding the label "node-role.kubernetes.io/master=''"
[mark-control-plane] Marking the node k8s-master01.computingforgeeks.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 "https://computingforgeeks.com/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.computingforgeeks.com:6443 --token sr4l2l.2kvot0pfalh5o4ik 
    --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18 
    --control-plane 

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

kubeadm join k8s-cluster.computingforgeeks.com:6443 --token sr4l2l.2kvot0pfalh5o4ik 
    --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18

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.computingforgeeks.com:6443
KubeDNS is running at https://k8s-cluster.computingforgeeks.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.computingforgeeks.com:6443 --token sr4l2l.2kvot0pfalh5o4ik 
    --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18 
    --control-plane

Step 6: Install network plugin on Master

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

kubectl apply -f https://docs.projectcalico.org/manifests/calico.yaml

You should see the following output.

configmap/calico-config created
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
clusterrole.rbac.authorization.k8s.io/calico-kube-controllers created
clusterrolebinding.rbac.authorization.k8s.io/calico-kube-controllers created
clusterrole.rbac.authorization.k8s.io/calico-node created
clusterrolebinding.rbac.authorization.k8s.io/calico-node created
daemonset.apps/calico-node created
serviceaccount/calico-node created
deployment.apps/calico-kube-controllers created
serviceaccount/calico-kube-controllers created

Confirm that all of the pods are running:

$ watch kubectl get pods --all-namespaces
NAMESPACE     NAME                                                         READY   STATUS    RESTARTS   AGE
kube-system   calico-kube-controllers-76d4774d89-nfqrr                     1/1     Running   0          2m52s
kube-system   calico-node-kpprr                                            1/1     Running   0          2m52s
kube-system   coredns-66bff467f8-9bxgm                                     1/1     Running   0          7m43s
kube-system   coredns-66bff467f8-jgwln                                     1/1     Running   0          7m43s
kube-system   etcd-k8s-master01.computingforgeeks.com                      1/1     Running   0          7m58s
kube-system   kube-apiserver-k8s-master01.computingforgeeks.com            1/1     Running   0          7m58s
kube-system   kube-controller-manager-k8s-master01.computingforgeeks.com   1/1     Running   0          7m58s
kube-system   kube-proxy-bt7ff                                             1/1     Running   0          7m43s
kube-system   kube-scheduler-k8s-master01.computingforgeeks.com            1/1     Running   0          7m58s

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
k8s-master01   Ready    master   64m   v1.18.3   135.181.28.113           Ubuntu 20.04 LTS   5.4.0-37-generic   docker://19.3.11

Step 7: Add worker nodes

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.computingforgeeks.com

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

kubeadm join k8s-cluster.computingforgeeks.com:6443 
  --token sr4l2l.2kvot0pfalh5o4ik 
  --discovery-token-ca-cert-hash sha256:c692fb047e15883b575bd6710779dc2c5af8073f7cab460abd181fd3ddb29a18

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-1.18" ConfigMap in the kube-system namespace
[kubelet-start] Writing kubelet configuration to file "https://computingforgeeks.com/var/lib/kubelet/config.yaml"
[kubelet-start] Writing kubelet environment file with flags to file "https://computingforgeeks.com/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.computingforgeeks.com   Ready    master   10m   v1.18.3
k8s-worker01.computingforgeeks.com   Ready       50s   v1.18.3
k8s-worker02.computingforgeeks.com   Ready       12s   v1.18.3

$ kubectl get nodes -o wide

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

Join new Kubernetes Worker Node to an existing Cluster

Step 8: Deploy application on cluster

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          16s

Step 9: Install Kubernetes Dashboard (Optional)

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

Storage guides:

Ceph Persistent Storage for Kubernetes with Cephfs

Persistent Storage for Kubernetes with Ceph RBD

How To Configure Kubernetes Dynamic Volume Provisioning With Heketi & GlusterFS

Learning courses:

Similar Kubernetes deployment guides:

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