Implement cloud-init data templating for getting node IP

Author: Tomy2e

docs/advanced.md

@@ -0,0 +1,58 @@
+# Advanced configurations
+
+## Use private IP in Kubeadm configurations
+
+When your nodes have both public and private IPs, Kubeadm will always advertise
+the public IP by default. This can be an issue if you want the control-plane to
+communicate through the Private Network and then block all public ingress traffic
+on your nodes using an Instance security group.
+
+To solve this, you can include the node's private IP in your Kubeadm configurations using
+the `[[[ .NodeIP ]]]` placeholder value. This placeholder value will be replaced
+by the provider with the private IP of the node. If a Private Network is not enabled
+in the `ScalewayCluster`, `[[[ .NodeIP ]]]` will be replaced with the public IP
+of the node instead.
+
+Here is an example of `KubeadmControlPlane` configuration:
+
+```yaml
+apiVersion: controlplane.cluster.x-k8s.io/v1beta1
+kind: KubeadmControlPlane
+metadata:
+  name: my-kubeadm-controlplane
+  namespace: default
+spec:
+  kubeadmConfigSpec:
+    initConfiguration:
+      localAPIEndpoint:
+        advertiseAddress: "[[[ .NodeIP ]]]"
+      nodeRegistration:
+        kubeletExtraArgs:
+          node-ip: "[[[ .NodeIP ]]]"
+    joinConfiguration:
+      controlPlane:
+        localAPIEndpoint:
+          advertiseAddress: "[[[ .NodeIP ]]]"
+      nodeRegistration:
+        kubeletExtraArgs:
+          node-ip: "[[[ .NodeIP ]]]"
+  # important: some fields were omitted...
+```
+
+Here is an example of `KubeadmConfigTemplate` configuration:
+
+```yaml
+apiVersion: bootstrap.cluster.x-k8s.io/v1beta1
+kind: KubeadmConfigTemplate
+metadata:
+  name: my-kubeadmconfig-template
+  namespace: default
+spec:
+  template:
+    spec:
+      joinConfiguration:
+        nodeRegistration:
+          kubeletExtraArgs:
+            node-ip: "[[[ .NodeIP ]]]"
+  # important: some fields were omitted...
+```

internal/service/scaleway/instance/instance.go

@@ -5,6 +5,8 @@ import (
 	"errors"
 	"fmt"
 	"slices"
+	"strings"
+	"text/template"
 	"time"
 
 	infrav1 "github.com/scaleway/cluster-api-provider-scaleway/api/v1alpha1"
@@ -84,7 +86,7 @@ func (s *Service) Reconcile(ctx context.Context) error {
 			return fmt.Errorf("failed to ensure control-plane lbs acls: %w", err)
 		}
 
-		if err := s.ensureCloudInit(ctx, server); err != nil {
+		if err := s.ensureCloudInit(ctx, server, nodeIP); err != nil {
 			return fmt.Errorf("failed to ensure cloud-init: %w", err)
 		}
 
@@ -558,7 +560,7 @@ func instanceIPsToStrings(ips []*instance.ServerIP) []string {
 	return out
 }
 
-func (s *Service) ensureCloudInit(ctx context.Context, server *instance.Server) error {
+func (s *Service) ensureCloudInit(ctx context.Context, server *instance.Server, nodeIP string) error {
 	if server.State != instance.ServerStateStopped {
 		return nil
 	}
@@ -574,12 +576,25 @@ func (s *Service) ensureCloudInit(ctx context.Context, server *instance.Server)
 			return err
 		}
 
+		// Apply custom templating on cloud-init bootstrap data.
+		tmpl, err := template.New("").Delims("[[[", "]]]").Parse(string(bootstrapData))
+		if err != nil {
+			return fmt.Errorf("failed to parse bootstrap data as template: %w", err)
+		}
+
+		tmplExec := &strings.Builder{} // tmplExec will contain the executed template.
+		tmplData := struct{ NodeIP string }{nodeIP}
+
+		if err := tmpl.ExecuteTemplate(tmplExec, "", tmplData); err != nil {
+			return fmt.Errorf("failed to execute bootstrap data template: %w", err)
+		}
+
 		if err := s.ScalewayClient.SetServerUserData(
 			ctx,
 			server.Zone,
 			server.ID,
 			cloudInitUserDataKey,
-			string(bootstrapData),
+			tmplExec.String(),
 		); err != nil {
 			return err
 		}