Kubeadm is a tool designed to simplify the process of creating Kubernetes clusters by providing kubeadm init
and kubeadm join
commands as best-practice "fast paths." - Kubernetes documentation
In this blog, we'll go through the step-by-step process of installing a Kubernetes cluster using Kubeadm.
Prerequisites
Before you begin, ensure you have the following:
Ensure you have a compatible Linux host (e.g., Debian-based and Red Hat-based distributions). In this blog, we're using Ubuntu which is a Debian-based OS.
At least 2 GB of RAM and 2 CPUs per machine.
Full network connectivity between all machines in the cluster.
Unique hostname, MAC address, and product_uuid for every node.
Ensure all the required ports are open for the control plane and the worker nodes. You can refer to Ports and Protocols or see the screenshot below.
Disable swap on all the nodes.
sudo swapoff -a
# disable swap on startup in /etc/fstab
sudo sed -i '/ swap / s/^/#/' /etc/fstab
Setup container runtime(Containerd)
To run containers in Pods, Kubernetes uses a container runtime. By default, Kubernetes employs the Container Runtime Interface (CRI)
to interact with your selected container runtime. Each node needs to have container runtime installed. In this blog, we'll use containerd
.
Run these instructions on all the nodes. I am using Ubuntu on all the nodes.
-
Enable IPv4 packet forwarding:
# sysctl params required by setup, params persist across reboots cat <<EOF | sudo tee /etc/sysctl.d/k8s.conf net.ipv4.ip_forward = 1 EOF # Apply sysctl params without reboot sudo sysctl --system
Run
sudo sysctl net.ipv4.ip_forward
to verify thatnet.ipv4.ip_forward
is set to 1 -
Specify and load the following kernel module dependencies:
cat <<EOF | sudo tee /etc/modules-load.d/k8s.conf overlay br_netfilter EOF sudo modprobe overlay sudo modprobe br_netfilter
-
Install containerd:
Add Docker's official GPG key:
sudo apt-get update sudo apt-get -y install ca-certificates curl sudo install -m 0755 -d /etc/apt/keyrings sudo curl -fsSL https://download.docker.com/linux/ubuntu/gpg -o /etc/apt/keyrings/docker.asc sudo chmod a+r /etc/apt/keyrings/docker.asc
Add the repository to Apt sources:
echo \ "deb [arch=$(dpkg --print-architecture) signed-by=/etc/apt/keyrings/docker.asc] https://download.docker.com/linux/ubuntu \ $(. /etc/os-release && echo "$VERSION_CODENAME") stable" | \ sudo tee /etc/apt/sources.list.d/docker.list > /dev/null
Install containerd
sudo apt-get update sudo apt-get -y install containerd.io
For more details, refer to the Official installation documentation
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Configure systemd cgroup driver for containerd
First, we need to create a containerd configuration file at the location
/etc/containerd/config.toml
sudo mkdir -p /etc/containerd sudo containerd config default | sudo tee /etc/containerd/config.toml
Now, we enable the systemd cgroup driver for the CRI in
/etc/containerd/config.toml
at section[plugins."io.containerd.grpc.v1.cri".containerd.runtimes.runc.options]
setSystemCgroup = true
OR we can just run
sudo sed -i "s/SystemdCgroup = false/SystemdCgroup = true/g" "/etc/containerd/config.toml"
Restart containerd
sudo systemctl restart containerd
Containerd should be running, check the status using:
sudo systemctl status containerd
Install kubeadm, kubelet and kubectl
Run these commands on all nodes. These instructions are for Kubernetes v1.30.
-
Install
apt-transport-https, ca-certificates, curl, gpg
packages
sudo apt-get update sudo apt-get install -y apt-transport-https ca-certificates curl gpg
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Download the public signing key for the Kubernetes package repositories
curl -fsSL https://pkgs.k8s.io/core:/stable:/v1.30/deb/Release.key | sudo gpg --dearmor -o /etc/apt/keyrings/kubernetes-apt-keyring.gpg
-
Add the
apt
repository for Kubernetes 1.30
echo 'deb [signed-by=/etc/apt/keyrings/kubernetes-apt-keyring.gpg] https://pkgs.k8s.io/core:/stable:/v1.30/deb/ /' | sudo tee /etc/apt/sources.list.d/kubernetes.list
-
Install kubelet, kubeadm and kubectl
sudo apt-get update sudo apt-get install -y kubelet kubeadm kubectl sudo apt-mark hold kubelet kubeadm kubectl
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This is optional, Enable the kubelet service before running kubeadm
sudo systemctl enable --now kubelet
Initialize the k8s control plane
Run these instructions only on the control plane node
-
kubeadm init
To initialize the control plane, run the
kubeadm init
command. You also need to choose a pod network add-on and deploy aContainer Network Interface (CNI)
so that your Pods can communicate with each other. Cluster DNS (CoreDNS) will not start until a network is installed.We will use Calico CNI, so set the
--pod-network-cidr=192.168.0.0/16
.
sudo kubeadm init --pod-network-cidr=192.168.0.0/16
Now, at the end of the
kubeadm init
command, you'll seekubeadm join
commandsudo kubeadm join <control-plane-ip>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash <hash>
copy it and keep it safe. -
Run the following commands to set kubeconfig to access the cluster using kubectl
mkdir -p $HOME/.kube sudo cp -i /etc/kubernetes/admin.conf $HOME/.kube/config sudo chown $(id -u):$(id -g) $HOME/.kube/config
Now, check the node using
$ kubectl get nodes NAME STATUS ROLES AGE VERSION ip-zzz-zz-z-zz NotReady control-plane 114s v1.30.2
The node is in
NotReady
state becausemessage: 'container runtime network not ready: NetworkReady=false reason:NetworkPluginNotReady message:Network plugin returns error: cni plugin not initialized' reason: KubeletNotReady
. After setting up the CNI, the node should be in a Ready state. -
Set Up a Pod Network
We must deploy a Container Network Interface (CNI) based Pod network add-on so that Pods can communicate with each other.
Install the calico operator on the cluster.
kubectl create -f https://raw.githubusercontent.com/projectcalico/calico/v3.28.0/manifests/tigera-operator.yaml
Download the custom resources necessary to configure Calico.
kubectl create -f https://raw.githubusercontent.com/projectcalico/calico/v3.28.0/manifests/custom-resources.yaml
Verify all the Calico pods are in running state.
$ kubectl get pods -n calico-system NAME READY STATUS RESTARTS AGE calico-kube-controllers-6f459db86d-mg657 1/1 Running 0 3m36s calico-node-ctc9q 1/1 Running 0 3m36s calico-typha-774d5fbdb7-s7qsg 1/1 Running 0 3m36s csi-node-driver-bblm8 2/2 Running 0 3m3
Verify that the node is in a running state
$ kubectl get nodes NAME STATUS ROLES AGE VERSION ip-xxx-xx-x-xx Ready control-plane 2m46s v1.30.2
Join the worker nodes
Ensure containerd
, kubeadm
, kubectl
, and kubelet
are installed on all worker nodes, then run sudo kubeadm join <control-plane-ip>:<control-plane-port> --token <token> --discovery-token-ca-cert-hash <hash>
, which you can find at the end of the kubeadm init
command's output.
Check the cluster state
Run these commands on the control-plane node since the worker nodes do not have the kubeconfig file.
-
Check if the worker nodes are joined to the cluster.
$ kubectl get nodes NAME STATUS ROLES AGE VERSION ip-xxx-xx-xx-xx Ready <none> 9m9s v1.30.2 ip-yyy-yy-yy-yy Ready <none> 23s v1.30.2 ip-zzz-zz-z-zz Ready control-plane 27m v1.30.2
To add a worker role to the worker node we can use
kubectl label node <node-name> node-role.kubernetes.io/worker=worker
command.
$ kubectl get nodes NAME STATUS ROLES AGE VERSION ip-xxx-xx-xx-xx Ready worker 12m v1.30.2 ip-yyy-yy-yy-yy Ready worker 3m51s v1.30.2 ip-zzz-zz-z-zz Ready control-plane 31m v1.30.2
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Check the workload running on the cluster
$ kubectl get pods -A NAMESPACE NAME READY STATUS RESTARTS AGE calico-apiserver calico-apiserver-6fcb65fbd5-n4wsn 1/1 Running 0 35m calico-apiserver calico-apiserver-6fcb65fbd5-nnggl 1/1 Running 0 35m calico-system calico-kube-controllers-6f459db86d-mg657 1/1 Running 0 35m calico-system calico-node-ctc9q 1/1 Running 0 35m calico-system calico-node-dmgt2 1/1 Running 0 18m calico-system calico-node-nw4t5 1/1 Running 0 9m49s calico-system calico-typha-774d5fbdb7-s7qsg 1/1 Running 0 35m calico-system calico-typha-774d5fbdb7-sxb5c 1/1 Running 0 9m39s calico-system csi-node-driver-bblm8 2/2 Running 0 35m calico-system csi-node-driver-jk4sz 2/2 Running 0 18m calico-system csi-node-driver-tbrrj 2/2 Running 0 9m49s kube-system coredns-7db6d8ff4d-5f7s5 1/1 Running 0 37m kube-system coredns-7db6d8ff4d-qj9r8 1/1 Running 0 37m kube-system etcd-ip-zzz-zz-z-zz 1/1 Running 0 37m kube-system kube-apiserver-ip-zzz-zz-z-zz 1/1 Running 0 37m kube-system kube-controller-manager-ip-zzz-zz-z-zz 1/1 Running 0 37m kube-system kube-proxy-dq8k4 1/1 Running 0 9m49s kube-system kube-proxy-t2sw9 1/1 Running 0 18m kube-system kube-proxy-xd6nn 1/1 Running 0 37m kube-system kube-scheduler-ip-zzz-zz-z-zz 1/1 Running 0 37m tigera-operator tigera-operator-76ff79f7fd-jj4kf 1/1 Running 0 35m
Conclusion
Setting up a Kubernetes cluster with Kubeadm involves a clear and structured process. You can create a functional cluster by meeting all prerequisites, configuring the container runtime, and installing Kubernetes components. Using Calico for networking ensures seamless pod communication. With the control plane and worker nodes properly configured and joined, you can efficiently manage and deploy workloads across your Kubernetes cluster.
Thank you for reading this blog; your interest is greatly appreciated, and I hope it helps you on your Kubernetes journey; in the next article, we'll explore running workloads in the Kubernetes cluster.
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