Kube-Hetzner

A highly optimized and auto-upgradable, HA-default & Load-Balanced, Kubernetes cluster powered by k3s-on-MicroOS and deployed for peanuts on Hetzner Cloud 🤑 🚀

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About The Project

ℹ️ For the moment this README is not synced with the current release, as we currently use the master branch for active development, please find the one that aligns with the latest stable release here.

Hetzner Cloud is a good cloud provider that offers very affordable prices for cloud instances, with data center locations in both Europe and the US.

The goal of this project is to create an optimal and highly optimized Kubernetes installation that is easily maintained, secure, and automatically upgrades. We aimed for functionality as close as possible to GKE's auto-pilot.

In order to achieve this, we built it on the shoulders of giants, by choosing openSUSE MicroOS as the base operating system, and k3s as the Kubernetes engine.

Please note that we are not affiliated to Hetzner, this is just an open source project striving to be an optimal solution for deploying and maintaining Kubernetes on Hetzner Cloud.

Features

• Maintenance free with auto-upgrade to the latest version of MicroOS and k3s.
• Proper use of the Hetzner private network to minimize latency and remove the need for encryption.
• Automatic HA with the default setting of three control-plane nodes and two agent nodes.
• Super-HA: Nodepools for both control-plane and agent nodes can be in different locations.
• Possibility to have a single node cluster with a proper ingress controller (Traefik).
• Ability to add nodes and nodepools when the cluster running.
• Traefik ingress controller attached to a Hetzner load balancer with proxy protocol turned on.
• Tons of flexible configuration options to suits all needs.

It uses Terraform to deploy as it's easy to use, and Hetzner provides a great Hetzner Terraform Provider.

Getting Started

Follow those simple steps, and your world's cheapest Kube cluster will be up and running in no time.

✔️ Prerequisites

First and foremost, you need to have a Hetzner Cloud account. You can sign up for free here.

Then you'll need to have terraform, kubectl cli, and hcloud the Hetzner cli. The easiest way is to use the homebrew package manager to install them (available on Linux, Mac, and Windows Linux Subsystem).

brew install terraform
brew install kubectl
brew install hcloud

💡 [Do not skip] Creating the terraform.tfvars file

1. Create a project in your Hetzner Cloud Console, and go to Security > API Tokens of that project to grab the API key. Take note of the key! ✅
2. Generate a passphrase-less ed25519 SSH key-pair for your cluster, take note of the respective paths of your private and public keys. Or, see our detailed SSH options. ✅
3. Copy terraform.tfvars.example to terraform.tfvars, and replace the values from steps 1 and 2. ✅
4. Make sure you have the latest Terraform version, ideally at least 1.1.0. You can check with terraform -v. ✅
5. (Optional) There are other variables in terraform.tfvars that could be customized, like Hetzner region, and the node counts and sizes.

It can also be used as a Terraform module, see the examples section, but basically you just copy the content of terraform.tfvars to the module body. More on the Kube-Hetzner Terraform module page.

🎯 Installation

terraform init --upgrade
terraform apply -auto-approve

It will take around 5 minutes to complete, and then you should see a green output with the IP addresses of the nodes.

Usage

When the cluster is up and running, you can do whatever you wish with it! 🎉

You can immediately kubectl into it (using the kubeconfig.yaml saved to the project's directory after the install). By doing kubectl --kubeconfig kubeconfig.yaml, but for more convenience, either create a symlink from ~/.kube/config to kubeconfig.yaml, or add an export statement to your ~/.bashrc or ~/.zshrc file, as follows (you can get the path of kubeconfig.yaml by running pwd):

export KUBECONFIG=/<path-to>/kubeconfig.yaml

Once you start with Terraform, it's best not to change the state manually in Hetzner, otherwise when you try to scale up or down, or even destroy the cluster, you'll get an error.

Scaling Nodes

Two things can be scaled, the number of nodepools or the count of nodes in these nodepools. You have two list of nodepools you can add to in terraform.tfvars, the control plane nodepool list and the agent nodepool list. Both combined cannot exceed 255 nodepools (you extremely unlikely to reach this limit). As for the count of nodes per nodepools, if you raise your limits in Hetzner, you can have up to 64,670 nodes per nodepool (also very unlikely to need that much).

There are some limitations (to scaling down mainly) that you need to be aware of:

Once the cluster is created, you can change nodepool count, and even set it to 0 (in the case of the first control-plane nodepool, the minimum is 1), you can also rename a nodepool (if the count is taken to 0), but should not remove a nodepool from the list after the cluster is created. This is due to how subnets and IPs are allocated. The only nodepools you can remove are the ones at the end of each list of nodepools.

However you can freely add others nodepools the end of the list if you want, and of course increase the node count. You can also decrease the node count, but make sure you drain the node in question before, otherwise it will leave your cluster in a bad state. The only nodepool that needs at least to have a count of 1 always, is the first control-plane nodepool, for obvious reasons.

High Availability

By default, we have 3 control planes and 3 agents configured, with automatic upgrades and reboots of the nodes.

If you want to remain HA (no downtime), it's important to keep a number of control planes nodes of at least 3 (2 minimum to maintain quorum when 1 goes down for automated upgrades and reboot), see Rancher's doc on HA.

Otherwise, it's important to turn off automatic upgrades of the OS only (k3s can continue to update without issue) for the control-plane nodes (when 2 or less control-plane nodes), and do the maintenance yourself.

Automatic Upgrade

By default, MicroOS gets upgraded automatically on each node, and reboot safely via Kured installed in the cluster.

As for k3s, it also automatically upgrades thanks to Rancher's system upgrade controller. By default it follows the k3s stable channel, but you can also change to latest one if needed, or specify a target version to upgrade to via the upgrade plan.

You can copy and modify the one in the templates for that! More on the subject in k3s upgrades basic.

If you wish to turn off automatic MicroOS upgrades on a specific node, you need to ssh into it and issue the following command:

systemctl --now disable transactional-update.timer

To turn off k3s upgrades, you can either set the k3s_upgrade=true label in the node you want, or set it to false. To just remove it, apply:

kubectl -n system-upgrade label node <node-name> k3s_upgrade-

Examples

Ingress with TLS

Here is an example of an ingress to run an application with TLS, change the host to fit your need in examples/tls/ingress.yaml and then deploy the example:

kubectl apply -f examples/tls/.

apiVersion: networking.k8s.io/v1
kind: Ingress
metadata:
  name: nginx-ingress
  annotations:
    traefik.ingress.kubernetes.io/router.tls: "true"
    traefik.ingress.kubernetes.io/router.tls.certresolver: le
spec:
  tls:
    - hosts:
        - example.com
  rules:
    - host: example.com
      http:
        paths:
          - path: /
            pathType: Prefix
            backend:
              service:
                name: nginx-service
                port:
                  number: 80

Single-node cluster

Running a development cluster on a single node, without any high-availability is possible as well. You need one control plane nodepool with a count of 1, and one agent nodepool with a count of 0.

In this case, we don't deploy an external load-balancer, but use the default k3s service load balancer on the host itself and open up port 80 & 443 in the firewall (done automatically).

Use as Terraform module

It is easy to use Kube-Hetzner as a Terraform module. To do so:

module "kube-hetzner" {
  source  = "kube-hetzner/kube-hetzner/hcloud"
  
  # insert the required variables here found in terraform.tfvars.example
}

Debugging

First and foremost, it depends, but it's always good to have a quick look into Hetzner quickly without having to login to the UI. That is where the hcloud cli comes in.

• Activate it with hcloud context create kube-hetzner, it will prompt for your Hetzner API token, paste that and hit enter.
• To check the nodes, if they are running, for instance, use hcloud server list.
• To check the network use hcloud network describe k3s.
• To see a look at the LB, use hcloud loadbalancer describe traefik.

Then for the rest, you'll often need to login to your cluster via ssh, to do that, use:

ssh root@xxx.xxx.xxx.xxx -i ~/.ssh/id_ed25519 -o StrictHostKeyChecking=no

Then, for control-plane nodes, use journalctl -u k3s to see the k3s logs, and for agents, use journalctl -u k3s-agent instead.

Last but not least, to see when the last reboot took place, you can use both last rebootand uptime.

Takedown

If you want to takedown the cluster, you can proceed as follows:

terraform destroy -auto-approve

And if the network is slow to delete, just issue hcloud network delete k3s to speed things up!

Also, if you had a full-blown cluster in use, it would be best to delete the whole project in your Hetzner account directly as operators or deployments may create other resources during regular operation.

History

This project has tried two other OS flavors before settling on MicroOS. Fedora Server, and k3OS. The latter, k3OS, is now defunct! However, our code base for it lives on in the k3os branch. Do not hesitate to check it out, it should still work.

There is also a branch where openSUSE MicroOS came preinstalled with the k3s RPM from devel:kubic/k3s, but we moved away from that solution as the k3s version was rarely getting updates. See the microOS-k3s-rpm branch for more.

Contributing

🌱 This project currently installs openSUSE MicroOS via the Hetzner rescue mode, which makes things a few minutes slower. If you could take a few minutes to send a support request to Hetzner, asking them to please add openSUSE MicroOS as a default image, not just an ISO, it would be wonderful. The more requests they receive the likelier they are to add support for it, and if they do, that would cut the deploy time by half. The official link to openSUSE MicroOS is https://get.opensuse.org/microos, and their OpenStack Cloud image has full support for Cloud-init, so it's a great option to propose to them!

About code contributions, they are greatly appreciated.

1. Fork the Project
2. Create your Branch (git checkout -b AmazingFeature)
3. Commit your Changes (git commit -m 'Add some AmazingFeature')
4. Push to the Branch (git push origin AmazingFeature)
5. Open a Pull Request

Acknowledgements

• k-andy was the starting point for this project. It wouldn't have been possible without it.
• Best-README-Template that made writing this readme a lot easier.
• Hetzner Cloud for providing a solid infrastructure and terraform package.
• Hashicorp for the amazing terraform framework that makes all the magic happen.
• Rancher for k3s, an amazing Kube distribution that is the very core engine of this project.
• openSUSE for MicroOS, which is just next level Container OS technology.