apricote.de/content/posts/ccm-from-scratch/_index.md

author	title	date	summary	description	tags	ShowBreadCrumbs	cover
Julian Tölle	Building a Kubernetes cloud-controller-manager	2023-09-06	A tutorial series to showcase the steps needed to build a Kubernetes Cloud Controller Manager. Intended to be your guide into better Kubernetes-compatibility for your own Infrastructure-as-a-Service Cloud.	This tutorial series tries to showcase the steps needed to build a first iteration of a Kubernetes Cloud Controller Manager. It can be adapted to any Cloud Provider and may be your guide into better Kubernetes-compatibility for your own Infrastructure-as-a-Service Cloud.	kubernetes	true	image responsiveImages caption cover.webp true dall-e with prompt "ship stearing towards clouds, a captain behind the steering wheel, cartoon, wide angle"

{{< collapse summary="Disclaimers" openByDefault=true >}}

Employer

I [work for Hetzner Cloud]({{< ref "/work" >}}) and this project was done during working hours as part of the Lab Days. During Lab Days, employees can choose to work on topics unrelated to their work.

Production Readiness

The code written in this series is not ready for production. You should not actually use the code I provide for your Kubernetes Cluster on Hetzner Cloud. Please use the official hcloud-cloud-controller-manager instead. {{</ collapse >}}

Introduction

What is a Cloud Controller Manager?

Source

• Controllers: Loop that reconciles reality with the desired state
• Controller Manager: Binary that runs a bunch of controllers
• Cloud Controller Manager: Part of the Kubernetes Control Plane, responsible for exposing Cloud Provider functionality inside the Kubernetes cluster.
• Controllers in CCMs:
  • Node Metadata
    • Match Kubernetes Node to Cloud API Server (/Instance/Droplet/...) and set spec.providerID
    • Label Kubernetes Nodes with metadata of the Node, including the Instance Type, Topology (Region, Zone)
    • Figure out the Network addresses of the Node and set them in status.addresses.
  • Node Lifecycle
    • The kubelet is usually responsible for creating the Node object in Kubernetes on its first startup.
    • This does not work well for the removal of the node, as the kubelet might not get a chance to do this. Instead, the Node Lifecycle controller regularly checks if the Node was deleted in the Cloud API, and if it was it also deletes the Node object in Kubernetes.
  • Service
    • Watches Service objects with type: LoadBalancer. Creates Cloud Load Balancers and configures them according to the Service and Node objects
  • Route
    • In Kubernetes, every Pod gets an IP address. This IP address needs to be available from every other pods network (by default). This is usually implemented as an Overlay Network through your CNI like Calico or Cilium.
    • If you are already using some kind of Private Networking functionality of your Cloud Provider, then you can use this instead to get rid of the additional Overlay Network and let the Cloud Provider handle the connectivity.
    • This is implemented by configuring Routes in the Private Network Routing Table that send all traffic to the Nodes spec.podCIDR to the Nodes private IP.

What is the Hetzner Cloud?

Source

• IaaS with: Servers, Load Balancers, Private Networks

Parts

This project got way longer than I expected, so I split everything up into 5 parts: