start part 3

content/posts/ccm-from-scratch-1/index.md

@@ -778,6 +778,119 @@ TODO output
 
 > Goal: Implement the Node controller with all features, deploy & verify
 
+Now that our side-quest is finished, we can finally go back to the part why you are all here: Implementing the controllers of our cloud-controller-manager.
+
+This part focuses on the Node controller. To [recap](TODO Link to part 1) its functionality:
+- _Node_
+  - 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.
+
+Luck has is, `k8s.io/cloud-provider` already implements most of the logic, so we can focus on the integration with our Cloud Provider (Hetzner Cloud in my case).
+Similar to the general `Cloud` interface from [Part 1](TODO LINK), this post focuses on the [InstancesV2](https://pkg.go.dev/k8s.io/cloud-provider@v0.28.2#InstancesV2) interface.
+
+Lets start by stubbing out the interface in a new file:
+
+```go
+package ccm
+// ccm/instances_v2.go
+
+import (
+  "context"
+  
+  cloudprovider "k8s.io/cloud-provider"
+	corev1 "k8s.io/api/core/v1"
+)
+
+type InstancesV2 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.InstancesV2 = InstancesV2{}
+
+func (i *InstancesV2) InstanceExists(ctx context.Context, node *corev1.Node) (bool, error) { 
+	// We return true for now, to avoid CCM removing any Nodes from the cluster.
+	return true, nil
+}
+
+func (i *InstancesV2) InstanceShutdown(ctx context.Context, node *corev1.Node) (bool, error) {
+	return false, nil
+}
+
+func (i *InstancesV2) InstanceMetadata(ctx context.Context, node *corev1.Node) (*cloudprovider.InstanceMetadata, error) {
+	return nil, nil
+}
+```
+
+### Creating our Cloud Provider Client
+
+Before we can make any requests to our Cloud Provider API, we need to read some credentials and create the client.
+As mentioned in Part 1, we are going to use [hcloud-go](https://github.com/hetznercloud/hcloud-go), but you can use whatever client you like for your case.
+Because we also need the client in other controllers, we will create it in `ccm.NewCloudProvider()` and save it to the `CloudProvider` struct.
+
+```go
+package ccm
+// ccm/cloud.go
+
+import (
+	"os"
+	
+	"github.com/hetznercloud/hcloud-go/hcloud"
+)
+
+type CloudProvider struct {
+	client *hcloud.Client
+}
+
+func NewCloudProvider(_ *config.CompletedConfig) cloudprovider.Interface {
+	// In Part 2 we setup a Kubernetes Secret with our Hetzner Cloud API token, that is mounted as
+	// the environment variable HCLOUD_TOKEN in our Pod.
+	token := os.Getenv("HCLOUD_TOKEN")
+	
+	client := hcloud.NewClient(
+    hcloud.WithToken(token),
+	  // Setting a custom user agent
+	  hcloud.WithApplication("ccm-from-scratch", ""),
+  )
+	
+	
+  return CloudProvider{client: client}
+}
+```
+
+We can now initialize the `InstancesV2` struct and pass the client to it:
+
+```go
+package ccm
+
+// ccm/instances_v2.go
+type InstancesV2 struct {
+	client *hcloud.Client
+}
+
+// ccm/cloud.go
+func (c CloudProvider) InstancesV2() (cloudprovider.InstancesV2, bool) {
+  return InstancesV2{client: c.client}, true
+}
+```
+
+When we start our program now, it should detect that the InstancesV2 interface is supported and start the Node & NodeLifecycle controllers.
+
+### InstanceMetadata
+
+// TODO: Start with everything inline, refactor it out in the next section
+
+### Refactoring
+
+### InstanceExists
+
+### InstanceShutdown
+
+### Testing (in prod!)
+
 ## (Part 4) Controller: Service (Load Balancers)
 
 > Goal: Setup Load Balancers so traffic reaches our cluster, set up an ingress in the dev env that uses the LB