Kubernetes (k8s) is an open-source, cloud-native, container orchestration and management platform. It’s the go-to way to automate the deployment, scaling, and maintenance of containerised applications across different nodes. From service discovery to auto-restarts, and from resource allocation tracking to compute utilisation and scaling; a well-configured k8s cluster can manage a lot on its own.
What is a Kubernetes Cluster?
How to install Kubernetes on Debian 9
Step 1. Install Docker on Debian 9 VMs
Step 2. Install Curl and https
Step 3. Add Kubernetes public key
Step 4. Add an apt repository
Step 5. Update the system and install Kubernetes modules
Step 6. Set hostnames
Step 7. Configure firewall
Step 8. Turn swap off
Step 9. Enable Kubelet
Deploying a Kubernetes Cluster on Debian 9
Step 1. kubeadm initialisation
Step 2. Create required directories and start managing Kubernetes cluster
Step 3. Set up Pod network for the Cluster
Step 4. Add nodes to your Kubernetes cluster
A Kubernetes cluster consists of a Master and at least one to several worker node(s). The Master is the virtual machine (VM) that administers all activities on your cluster. A node is a VM that serves as a worker machine in your k8s cluster to host running applications. We strongly recommend you only use VMs aka Cloud Servers to run Kubernetes, not system containers aka VPS, as these can cause issues with k8s.
A node is comprised of the Kubelet, a container runtime, and the kube-proxy. The k8s installation’s three core modules: Kubelet, kubeadm, and kubectl are agents that control the node and communicate with the Kubernetes Master. Once they have been installed and other configurations done, you will be able to create your first k8s cluster. You can manage this cluster from the command line on your kubemaster node.
Every Kubernetes instance runs on top of a container runtime, which is software responsible for managing container operations. Containers in this case are not virtualised servers but rather a solution that packages code and dependencies to run a single application (service) in an isolated (containerised) environment, essentially disassociating applications from the host machine. The most popular and recommended one is Docker, and it’s the one we will use for the purpose of this guide. However, if you want to install a different underlying container runtime, you can harness the power of the Container Runtime Interface and use basically any runtime you want.
Kubernetes groups containers into pods, its most basic operational unit, which are basically just groups of containers running on the same node. Pods are connected over a network and share storage resources.
In order to connect your nodes or VMs and make them private, make sure to choose a hosting company who provides a Virtual Local Area Network (VLAN) with their VMs. We offer a VLAN add-on to our Cloud Servers for R200 per month.
• Multiple Debian 9 VMs (Cloud Servers) to house the Master and worker nodes.
• Docker or any other container runtime.
• User with
root privileges on every server.
Use our guide on How to install Docker on Debian 9 and 10
Your final output should be as shown below:
First, we need to install curl and https on every machine. Use the following commands:
sudo apt install curl
sudo apt-get install -y apt-transport-https
Now get and add the key
sudo curl -s https://packages.cloud.google.com/apt/doc/apt-key.gpg | apt-key add -
Next, we need to create a file for our new apt repository. Use the following command:
cat <<EOF | sudo tee /etc/apt/sources.list.d/kubernetes.list deb https://apt.kubernetes.io/ kubernetes-xenial main EOF
To update your system, enter:
sudo apt-get update
After the command finishes execution, install the Kubernetes modules using:
apt-get install -y kubelet kubeadm kubectl
Set the appropriate hostnames for your Master and worker nodes:
sudo hostnamectl set-hostname "master-node" exec bash
sudo hostnamectl set-hostname "w-node1" exec bash
Now open the /etc/hosts file and edit the hostnames for your worker nodes:
sudo cat <<EOF>> /etc/hosts 10.168.10.207 master-node 10.168.10.208 node1 W-node1 10.168.10.209 node2 W-node2 EOF
For seamless communication across multiple nodes, we need to define rules in firewall. Use the following commands on your Master node to do so:
sudo ufw allow 6443/tcp sudo ufw allow 2379/tcp sudo ufw allow 2380/tcp sudo ufw allow 10250/tcp sudo ufw allow 10251/tcp sudo ufw allow 10252/tcp sudo ufw allow 10255/tcp sudo ufw reload
We also need to execute these commands on each of the worker nodes:
sudo ufw allow 10251/tcp sudo ufw allow 10255/tcp sudo ufw reload
For Kubelet to work, we also need to disable swap on all of our VMs. Use the following command to turn swap off:
sudo swapoff -a
Finally, we need to enable the kubelet service. Use this command:
sudo systemctl enable kubelet
This concludes our installation and configuration of Kubernetes on Debian 9. We will now share the steps for deploying a k8s cluster.
To launch a new Kubernetes cluster instance, you need to initialise kubeadm. Use the following command:
sudo kubeadm init
This command may take several minutes to execute. Upon success, you should get logs similar to those in this screenshot:
You will also get an auto-generated command at the end of the output. Copy the text following the line
Then you can join any number of worker nodes by running the following on each as root: as highlighted in the above screenshot and save it somewhere safe. We will use this to add worker nodes to our cluster.
Note: If you forgot to copy the command, or have misplaced it, don’t worry. You can retrieve it again by entering the following command:
sudo kubeadm token create --print-join-command
In order to start managing your cluster, you need to create a directory and assume ownership. Run the following commands 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
Pods within a cluster are connected via the pod network. At this point, it’s not working. This can be verified by entering the following two commands:
sudo kubectl get nodes
sudo kubectl get pods --all-namespaces
As you can see, the status of master–node is
NotReady. The CoreDNS service is also not running. To fix this, run the following commands:
kubectl apply -f https://raw.githubusercontent.com/coreos/flannel/master/Documentation/kube-flannel.yml
You should get the following output:
And now, if you verify the statuses of your node and CoreDNS service, you should get
Running like seen below:
As a final step, you need to add worker nodes to your cluster. We will use the kubeadm join auto-generated token in Step 1. here.
Run your own version of the following command on all of the worker node VMs, meaning you have to replace
220.127.116.11:6443with your own machine’s IP address.
kubeadm join 18.104.22.168:6443 --token v9qxex.i6jant8m2r0zxhhk --discovery-token-ca-cert-hash sha256:b0cda6d2e64a8a65ad5f439e06c3cb489c3d7f6f4e0c094ebb2556037153dc4b
On successful addition, you should get the following output:
Running the following command on the
master-node should show your newly added node.
sudo kubectl get nodes
To set the role for your worker node, use the following command:
sudo kubectl label node w-node1 node-role.kubernetes.io/worker=worker
Now you’re all set up.
Got Ubuntu VMs? Learn How to install Kubernetes and deploy a cluster with Docker on Ubuntu 18.04
Got CentOS VMs? Learn How to install Kubernetes and deploy a cluster with Docker on CentOS 7
Want to set up Kubernetes on Windows? How to install Kubernetes cluster on Windows Server 2019 worker nodes with Ubuntu Master