infra/capi: add a platform-specific post-destroy hook

For some platforms, it might be necessary to execute destroy tasks
_after_ the cluster-api system has stopped so that it won't try to
reconcile the changes.

This commits adds a post-destroy hook that runs during the bootstrap
destroy process but after cluster-api has shutdown.

Author: r4f4

pkg/infrastructure/clusterapi/clusterapi.go

@@ -394,9 +394,9 @@ func (i *InfraProvider) DestroyBootstrap(ctx context.Context, dir string) error
 
 	machineDeletionTimeout := 5 * time.Minute
 	logrus.Infof("Waiting up to %v for bootstrap machine deletion %s/%s...", machineDeletionTimeout, machineNamespace, machineName)
-	ctx, cancel := context.WithTimeout(ctx, machineDeletionTimeout)
-	wait.UntilWithContext(ctx, func(context.Context) {
-		err := sys.Client().Get(ctx, client.ObjectKey{
+	cctx, cancel := context.WithTimeout(ctx, machineDeletionTimeout)
+	wait.UntilWithContext(cctx, func(context.Context) {
+		err := sys.Client().Get(cctx, client.ObjectKey{
 			Name:      machineName,
 			Namespace: machineNamespace,
 		}, &clusterv1.Machine{})
@@ -410,14 +410,25 @@ func (i *InfraProvider) DestroyBootstrap(ctx context.Context, dir string) error
 		}
 	}, 2*time.Second)
 
-	err = ctx.Err()
+	err = cctx.Err()
 	if err != nil && !errors.Is(err, context.Canceled) {
 		logrus.Warnf("Timeout deleting bootstrap machine: %s", err)
-	} else {
-		logrus.Infof("Finished destroying bootstrap resources")
 	}
 	clusterapi.System().Teardown()
 
+	if p, ok := i.impl.(PostDestroyer); ok {
+		postDestroyInput := PostDestroyerInput{
+			Metadata: *metadata,
+		}
+		if err := p.PostDestroy(ctx, postDestroyInput); err != nil {
+			return fmt.Errorf("failed during post-destroy hook: %w", err)
+		}
+		logrus.Debugf("Finished running post-destroy hook")
+	} else {
+		logrus.Infof("no post-destroy requirements for the %s provider", i.impl.Name())
+	}
+
+	logrus.Infof("Finished destroying bootstrap resources")
 	return nil
 }
 

pkg/infrastructure/clusterapi/types.go

@@ -106,3 +106,14 @@ type BootstrapDestroyInput struct {
 	Client   client.Client
 	Metadata types.ClusterMetadata
 }
+
+// PostDestroyer allows platform-specific behavior after bootstrap has been destroyed and
+// ClusterAPI has stopped running.
+type PostDestroyer interface {
+	PostDestroy(ctx context.Context, in PostDestroyerInput) error
+}
+
+// PostDestroyerInput collects args passed to the PostDestroyer hook.
+type PostDestroyerInput struct {
+	Metadata types.ClusterMetadata
+}