- 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](https://kubernetes.io/docs/reference/labels-annotations-taints/#nodekubernetesioinstance-type), Topology ([Region](https://kubernetes.io/docs/reference/labels-annotations-taints/#topologykubernetesioregion), [Zone](https://kubernetes.io/docs/reference/labels-annotations-taints/#topologykubernetesiozone))
- 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.
> Goal: Get a compilable binary running k/cloud-provider with no controllers yet
### Dependencies
As all ~~good~~ software does, we [stand on the shoulders of giants](https://xkcd.com/2347/). Let us review the two main dependencies that our code will use:
Thankfully, `k8s.io/cloud-provider` provides an example entrypoint to get us started with out CCM. Lets review the code to make sure we understand what is happening:
```go
package main
// [Imports]
// The main function is called as the entrypoint of our Go binary.
func main() {
// k8s.io/cloud-provider has an elaborate way to read the configuration from flags.
// I found this very tedious to debug, but at least we do not have to do this ourselves.
klog.Fatalf("unable to initialize command options: %v", err)
}
// Can be used to add custom flags to the binary, we dont need this.
fss := cliflag.NamedFlagSets{}
// This initializes the CLI command. The arguments are interesting, so lets take a closer look:
command := app.NewCloudControllerManagerCommand(
// The options we initialized earlier.
ccmOptions,
// This is a custom function that needs to return a [cloudprovider.Interface],
// we will get to this soon.
cloudInitializer,
// This defines which controllers are started, if wanted,
// one can add additional controller loops heroe
app.DefaultInitFuncConstructors,
// Kubernetes v1.28 renamed the controllers to more sensible names, this
// map makes it so that old command-line arguments (--controllers) still work
names.CCMControllerAliases(),
// Our optional additional flags
fss,
// A [<-chanstruct{}]thatcanbeusedtoshutdowntheCCMondemand,
// we do not need this.
wait.NeverStop,
)
// Actually run the command to completion.
code := cli.Run(command)
os.Exit(code)
}
```
Now, this does not compile right now. We use the undefined `cloudInitalizer` method. The method signature we need to implement is `(*config.CompletedConfig) cloudprovider.Interface`. The sample code includes this method, but I found it overly complex for our small CCM, so we will implement it ourselves. Lets take a closer look at the interface we need to return in the next section.
This is the entrypoint into the functionality we can (and will!) implement for our CCM. The interface includes an initializer, two cloud-provider metadata methods and a bunch of Getter functions to other interfaces that implement the actual functionality.
Before we can write the `cloudInitializer` method from above, lets prepare a struct that implements the interface:
```go
package ccm
// ccm/cloud.go
import (
cloudprovider "k8s.io/cloud-provider"
)
type CloudProvider struct {}
// Let's try to assign our struct to a var of the interface we try to implement.
// This way we get nice feedback from our IDE if we break the contract.
var _ cloudprovider.Interface = CloudProvider{}
// Can be used to setup our own controllers or goroutines that need to talk to
//Kubernetes. Not needed for our implementation, so we will leave it empty.
Now that we have a struct implementing the interface, lets create our `cloudInitializer` method. We will actually do this in the same file as our struct:
```go
// ccm/cloud.go
// Just create a new struct for now, we will add some more stuff to this later.
- If this topic does not interest you, you can safely skip ahead! While we use what we built in the following parts, you can still understand what is going on without reading this article.
Lets start by listing the requirements for our development environment:
- Single command to start the environment
- Working Kubernetes Cluster
- Running on Hetzner Cloud servers (as we target this environment with our cloud-controller-manager, you can substitute in your own cloud provider)
- Some way to deploy & debug our code
I have chosen the following technologies to implement this:
- Terraform Infrastructure-as-Code
- Using the [`terraform-provider-hcloud`](https://github.com/hetznercloud/terraform-provider-hcloud) to manage the Hetzner Cloud resources
- Using the `kubernetes`&`helm` providers to add the required resources to the cluster
- k3s through k3sup for the Kubernetes cluster
- Skaffold for the deployment & debugging
These tools should be installed locally:
- k3sup
- skaffold
- helm
- kubectl
- terraform
### Terraform
Terraform is an Infrastructure-as-Code tool. It allows us to define our infrastructure in a declarative way and then apply the changes to our cloud provider. If you have never used it before, I would recommend checking out some of their [tutorials](https://developer.hashicorp.com/terraform/tutorials) to get you started.
I will only `apply` our configuration at the end, to keep this post short. If you are developing this, I would recommend running `terraform plan`&`terraform apply` in between the steps to make sure everything so far works as expected.
Let us create our main terraform file:
```hcl
# dev-env.tf
terraform {
# In this block we will later define all providers we use.
required_providers {}
}
```
#### SSH Key
As we try to keep the development environment mostly self-contained, we start by creating an SSH Key that we can use to connect to our servers:
```hcl
terraform {
required_providers {
tls = {
source = "hashicorp/tls"
version = "4.0.4"
}
local = {
source = "hashicorp/local"
version = "2.4.0"
}
}
}
# This will generate a new random private key and save it to the Terraform state
resource "tls_private_key" "ssh" {
algorithm = "ED25519"
}
# This writes out the private key to a file in the current directory.
# We can use this to connect to our servers through SSH later.
resource "local_sensitive_file" "ssh" {
content = tls_private_key.ssh.private_key_openssh
filename = "${path.module}/.dev-env.ssh"
}
```
Now is a good time to add some Terraform specific files to our `.gitignore`:
```gitignore
# .gitignore
# Directory created by terraform for caches & internal state
.terraform
# The terraform state
terraform.tfstate
# Terraform makes a backup of the state before any operation
terraform.tfstate.backup
# Our private key we wrote in local_sensitive_file.ssh
.dev-env.ssh
# We will use this file in the next step to load credentials for the hcloud provider
credentials.auto.tfvars
# We will save the kubeconfig to this path in a later step
kubeconfig.yaml
```
#### Hetzner Cloud Resources
We will need:
- An SSH Key
- A Network & Subnet (for the `Routes` controller)
- A Control Plane Server
- 0 to X Worker Servers
To access the Hetzner Cloud API, we need to configure the provider with a token:
```hcl
terraform {
required_providers {
# Add to the others
hcloud = {
source = "hetznercloud/hcloud"
version = "1.42.1"
}
}
}
variable "hcloud_token" {
type = string
sensitive = true
}
# Configure the Hetzner Cloud Provider
provider "hcloud" {
token = var.hcloud_token
}
```
Now we can create create a new project in the [Clound Console](https://console.hetzner.cloud) and [generate a new API Token](https://docs.hetzner.com/cloud/api/getting-started/generating-api-token). This token will be saved in `credentials.auto.tfvars`. Because the file has the suffix `auto.tfvars`, Terraform will automatically use it.
```terraform
# credentials.auto.tfvars
hcloud_token = "YOUR_TOKEN"
```
Next, create the SSH Key:
```terraform
resource "hcloud_ssh_key" "default" {
name = "ccm-from-scratch dev env"
# Using the public key from the SSH Key we generated earlier
# This makes sure that the server is fully initialized before we install the Kubernetes cluster
provisioner "remote-exec" {
inline = ["cloud-init status --wait"]
}
}
resource "hcloud_server_network" "control" {
server_id = hcloud_server.control.id
subnet_id = hcloud_network_subnet.cluster.id
}
```
As we want to be able to scale the number of worker nodes, we will use a `count` to create multiple servers, besides that and the name prefix, the configuration are the same:
```terraform
variable "worker_count" {
type = number
default = 0
}
resource "hcloud_server" "worker" {
count = var.worker_count
name = "ccm-from-scratch-worker-${count.index}"
server_type = "cpx11"
location = "fsn1"
image = "ubuntu-22.04"
ssh_keys = [hcloud_ssh_key.default.id]
}
resource "hcloud_server_network" "control" {
for_each = hcloud_server.worker
server_id = each.id
subnet_id = hcloud_network_subnet.cluster.id
}
```
#### Kubernetes Cluster
As mentioned earlier, we will use `k3sup` to install `k3s` and other dependencies on the servers and join them to the Cluster.
We will use the `null_resource` and a local provisioner to run these commands locally as soon as the servers are ready. The control plane server needs a different command from the worker nodes, so we will use two resources.
```terraform
terraform {
required_providers {
null = {
source = "hashicorp/null"
version = "3.2.1"
}
}
}
# We need to define some additional configuration values for the Kubernetes cluster
locals {
# The CIDR range for the Pods, must be included in the range of the
# network (10.0.0.0/8) but must not overlap with the Subnet (10.0.0.0/24)
cluster_cidr = "10.244.0.0/16"
# Path to write the kubeconfig to, should be the same as the path in our gitignore from earlier.
# path.module is the directory the `dev-env.tf` file is in.
Nice! We now have a working Kubernetes Cluster, so let's deploy our CNI solution Cilium to it. We are going to use the Cilium Helm Chart & and the `helm` Provider for Terraform to install it:
```terraform
terraform {
required_providers {
# Add to the others
helm = {
source = "hashicorp/helm"
version = "2.11.0"
}
}
}
# As with the hcloud provider, we need to configure Helm and tell it how to connect to the cluster.
# k3sup wrote the config to a local file, and luckily the provider supports reading this BUT we need to make sure that the file is actually written / the Cluster is initialized before we can use it. Terraform has the `depends_on` we can use the local terraform provider to read it:
# TODO, finalize description above, maybe make actual text?
data "local_sensitive_file" "kubeconfig" {
# Kubeconfig is only written after control-plane is initialized finished
