How to setup 2 node cluster on k3s?

In this post, we are going to take look at Lightweight Kubernetes engine k3s that can run on edge, IoT, and appliances. Rancher k3s is great for offline development, prototyping, and testing purpose. You can very well use it on a VM as a small, cheap, reliable k8s for CI/CD.

What is k3s?

k3s is a fully compliant Kubernetes distribution with the following changes:

1. Packaged as a single binary.
2. Lightweight storage backend based on sqlite3 is the default storage mechanism. etcd3, MySQL, Postgres also available.
3. A simple launcher that handles a lot of the complexity of TLS and options.
4. Secure by default with reasonable defaults for lightweight environments.
5. Minimal to no OS dependencies. k3s packages require following dependencies
   • containerd
   • Flannel
   • CoreDNS
   • CNI
   • Host utilities (iptables, socat, etc)
   • Ingress controller (traefik)
   • An embedded service load balancer
   • An embedded network policy controller

In the next section, we will look at how to install and deploy sample application on to K3s cluster.

Step#1. Install K3s

In the below steps, we would be installing the k3s cluster, it would install a limited set of components like api-server, controller-manager, scheduler, kubelet, cni, kube-proxy.

Pre-requisites

• k3s is officially supported and tested on the following operating systems but it can run on any of flavor of Linux
  • Ubuntu 16.04 (amd64)
  • Ubuntu 18.04 (amd64)
  • Raspbian Buster
• Minimum recommendations on Hardware
  • RAM: 512MB Minimum
  • CPU: 1 Minimum
• For detailed installation requirements, please check here.

k3s can be deployed via installation script located at https://get.k3s.io, use the following command to install.

curl -sfL https://get.k3s.io | sh -

To avoid colliding with a kubectl already installed and to avoid overwriting any existing Kubernetes configuration file, k3s adds a k3s.kubectl command. If you are only using k3s, consider adding an alias command.

Step#2. Verify Installation

At this point you have installed k3s, check whether the newly deployed node is in Ready state using the following command.

Step#3. Deploy sample application

At this point, you have a fully functional Kubernetes cluster. The following command will deploy the Nginx web application.

kubectl run nginx --image nginx:alpine

Once Nginx has been deployed, the application can be exposed with the following command.

k3s kubectl expose deployment nginx \
--port 80 \
--target-port 80 \
--type ClusterIP \
--selector=run=nginx \
--name nginx

Now that services are exposed outside, we can launch lynx a terminal-based web browser to access the Nginx application using the following command.

export CLUSTER_IP=$(k3s kubectl get svc/nginx -o go-template='{{(index .spec.clusterIP)}}')
echo CLUSTER_IP=$CLUSTER_IP
lynx $CLUSTER_IP:80

Congrats! now you have a deployed Nginx application to a fully functional Kubernetes cluster using k3s.

In the next section, we will look at how to install and configure 2-nodes to this k3s cluster.

Step#4. Install Worker nodes

To install on worker nodes and add them to the cluster, run the installation script with the K3S_URL and K3S_TOKEN environment variables.

curl -sfL https://get.k3s.io | K3S_URL=https://<server>:6443 K3S_TOKEN=<token> sh -

Now go back to Master node, check whether the newly deployed node is in Ready state using the following command.

Install the next worker node and add them to the cluster using the following command:

curl -sfL https://get.k3s.io | K3S_URL=https://<server>:6443 K3S_TOKEN=<token> sh -

Now go back to Master node, check whether the newly deployed node is in Ready state using the following command.

Congrats! now we have fully functional 2-node Kubernetes cluster using K3s.

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Useful Resources :

• K3s Documentation
• Get smallest, fastest, fully-conformant MicroK8s Kubernetes
• 10 BEST Kubernetes monitoring tools
• Kubernetes Tutorial : Distributed tracing with Jaeger
• Tutorial : Helm package manager for Kubernetes
• Implementing Policies in Kubernetes
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