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Andy Gnias
Andy Gnias

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Setting up a k3s Server and Agent Node

Introduction

For as easy as k3s is to use, I had a difficult time finding a simple guide for setting up a Server-Agent configuration on two separate servers. In this post, I hope to provide that guide without requiring you to download any extra dependencies or use any other tools besides the scripts provided by k3s.

I used AWS EC2 instances as my VMs, so instructions will be slightly AWS specific, but should work on any two Linux servers configured to communicate with each other.

VM Setup

Provision Servers

First, we'll need to provision two Linux servers. I used two t2.small images, which is about as low as you'd want to go even when just running a sample app.

It's also worth assigning a permanent IP address to these servers via Elastic IP if you plan on using them more than once. Instructions for doing so are provided by AWS here.

Log onto each VM

Once you have your VMs up and running, pick one to be the Server and one to be the Agent. Get the hostname of each by running hostname -i and store both values in the ~/.bashrc file on both the server and the agent like so:

export k3sserver=<value of hostname -i on k3s server>
export k3sagent=<value of hostname -i on k3s agent>
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We will also use these values to configure the AWS Security Group.

Update AWS Security Group

Security group rules must be added to allow you to SSH into the VMs you created from your localhost, and also to SSH to and from the k3s server and agent. The rules for doing so are provided in the table below.

Type Port Range Source Purpose
SSH 22 IP from http://checkip.amazonaws.com/ SSH from localhost to Server and Agent
All Traffic All Value of $k3sserver SSH from Server to Agent
All Traffic All Value of $k3sagent SSH from Agent to Server

These rules are added to the Security Group's Inbound Rules (instructions for doing so can be found here).

Configure SSH keys

On both the k3s Server and Agent, run the following

cd ~/.ssh
ssh-keygen
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Hit enter at each of the prompts. This should result in an id_rsa private key and an id_rsa.pub public key being created. Copy the contents of id_rsa.pub on the server, and paste them on a new line into ~/.ssh/authorized_keys on the agent. Do the same for the agent, copying the contents from id_rsa.pub on the agent and pasting them on a new line in ~/.ssh/authorized_keys on the server.

You should now be able to ssh into the Agent from the Server, and vice versa.

Configure the VMs

On the Server and Agent, run the following script to run and configure Docker.

sudo yum update -y
sudo amazon-linux-extras install -y docker
sudo systemctl enable docker.service
sudo systemctl enable containerd.service
sudo service docker start
sudo usermod -a -G docker ec2-user
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After running, exit and log back in. Run sudo visudo and append the following to the secure_path value: :/usr/local/bin.

Defaults  secure_path="/usr/bin:/usr/sbin:/bin:/sbin:/usr/local/bin"
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Note that your secure path may have more paths before /usr/local/bin. This is OK. Adding this path allows you to run Docker on each instance without needing to precede every command with sudo.

Server Configuration

On the Server, run:

curl -sfL https://get.k3s.io | sh -s - --docker
sudo chmod 755 /etc/rancher/k3s/k3s.yaml
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Confirm the Server is ready with the following commands:

  • k3s kubectl get node - Should display 1 running node with roles control-plane,master
  • sudo service k3s status - Should show the service as running

Agent Configuration

On the Agent, run the following command, setting NODE_TOKEN to the contents of the file /var/lib/rancher/k3s/server/node-token on the Server instance:

curl -sfL https://get.k3s.io | K3S_URL=https://$k3sserver:6443 K3S_TOKEN=$NODE_TOKEN sh -s - --docker
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Confirm the Agent service is running with the following commands:

sudo service k3s-agent status
journalctl -f -u k3s-agent.service
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Then, on the Server VM, run kubectl get nodes. The Agent node should now appear without a tag. Add a tag with the following command:

kubectl label node <node name from kubectl get nodes> node-role.kubernetes.io/worker=worker
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Running kubectl get nodes again should show the Agent node with a tag. At this point, we've established that the Server and Agent are communicating with each other and k3s is ready for use!

Additional Reading

There's a ton of resources available to test k3s with. If you're looking for a place to start, I recommend Digital Ocean's Getting Started with Containers and Kubernetes: A DigitalOcean Workshop Kit for running a simple Flask app.

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