This article will show you how to install K3s onto a new Ubuntu 20.04 LTS machine for use with Coder.

K3s is a lightweight Kubernetes distribution that works well for single-node or multi-node clusters. For single-user trial purposes, you may want to consider the options in Coder for Docker.

This installation method is not officially supported or tested by Coder. If you have questions or run into issues, feel free to reach out using our community Slack channel.

We do not recommend using K3s for production deployments of Coder.

Prerequisites

Before proceeding, please make sure that:

• You have an Ubuntu 20.04 machine: This can be a bare metal or a virtual machine.

  Ensure that the machine's specs satisfy Coder's resource requirements, since your experience with Coder is dependent on your system specs.

• You have the following software installed on your machine:

  • helm

• Your network policy or firewall accepts incoming traffic on:

  • Port 80 (HTTP)
  • Port 443 (HTTPS)
  • Optional: Port 6443 (Kubernetes API)

Step 1: Install K3s with Calico

The following steps are based on Calico's quickstart guide for setting up K3s. However, you will disable K3s' default network policies and Traefik in favor of Calico and nginx-ingress.

1. Create a single-node K3s cluster:

   curl -sfL https://get.k3s.io | K3S_KUBECONFIG_MODE="644" INSTALL_K3S_EXEC="--flannel-backend=none --cluster-cidr=192.168.0.0/16 --disable-network-policy --disable=traefik" sh -
   

   Per the Calico docs:

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

   K3s installer generates kubeconfig file in /etc with limited permissions; by using the K3S_KUBECONFIG_MODE environment, you are assigning the necessary permissions to the file and making it accessible for other users.

2. Install the Calico operator and CRDs (Calico implements Kubernetes pod networking and policy enforcement):

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

3. Confirm that all of the pods are running:

   watch kubectl get pods --all-namespaces
   

Step 2: Allow IP Forwarding

Modify Calico to enable IP forwarding, which is needed for container networking.

vim /etc/cni/net.d/10-calico.conflist

kubectl edit cm cni-config -n calico-system

Under container_settings, set allow_ip_forwarding to true:

"container_settings": {
   "allow_ip_forwarding": true
}

Step 3: Copy over the kubeconfig

Occasionally, Helm will not recognize the K3s cluster (see k3s-io/k3s#1126 for more information).

If this happens, but you want to interface with the cluster from your local machine, copy /etc/rancher/k3s/k3s.yaml to ~/.kube/config.

After copying this file from the K3s node to your local workstation:

• Ensure that you replace localhost or 127.0.0.1 with the host's public IP address in the copied file
• Ensure that your firewall permits traffic through port 443

# on the host machine:
cp /etc/rancher/k3s/k3s.yaml ~/.kube/config

Next steps