Merge pull request kubernetes#84523 from rajansandeep/skipmigration

Retain CoreDNS corefile when migration fails in kubeadm

cmd/kubeadm/app/phases/addons/dns/dns.go

@@ -236,9 +236,17 @@ func createCoreDNSAddon(deploymentBytes, serviceBytes, configBytes []byte, clien
 	if err != nil {
 		return errors.Wrap(err, "unable to fetch CoreDNS current installed version and ConfigMap.")
 	}
+
+	var hasCoreDNSMigrationFailed bool
 	if IsCoreDNSConfigMapMigrationRequired(corefile) {
 		if err := migrateCoreDNSCorefile(client, coreDNSConfigMap, corefile, currentInstalledCoreDNSVersion); err != nil {
-			return err
+			// Errors in Corefile Migration is verified during preflight checks. This part will be executed when a user has chosen
+			// to ignore preflight check errors.
+			hasCoreDNSMigrationFailed = true
+			klog.Warningf("the CoreDNS Configuration was not migrated: %v. The existing CoreDNS Corefile configuration has been retained.", err)
+			if err := apiclient.CreateOrRetainConfigMap(client, coreDNSConfigMap, kubeadmconstants.CoreDNSConfigMap); err != nil {
+				return err
+			}
 		}
 	} else {
 		if err := apiclient.CreateOrUpdateConfigMap(client, coreDNSConfigMap); err != nil {
@@ -281,9 +289,16 @@ func createCoreDNSAddon(deploymentBytes, serviceBytes, configBytes []byte, clien
 		return errors.Wrapf(err, "%s Deployment", unableToDecodeCoreDNS)
 	}
 
-	// Create the Deployment for CoreDNS or update it in case it already exists
-	if err := apiclient.CreateOrUpdateDeployment(client, coreDNSDeployment); err != nil {
-		return err
+	// Create the deployment for CoreDNS or retain it in case the CoreDNS migration has failed during upgrade
+	if hasCoreDNSMigrationFailed {
+		if err := apiclient.CreateOrRetainDeployment(client, coreDNSDeployment, kubeadmconstants.CoreDNSDeploymentName); err != nil {
+			return err
+		}
+	} else {
+		// Create the Deployment for CoreDNS or update it in case it already exists
+		if err := apiclient.CreateOrUpdateDeployment(client, coreDNSDeployment); err != nil {
+			return err
+		}
 	}
 
 	coreDNSService := &v1.Service{}

cmd/kubeadm/app/phases/upgrade/preflight.go

@@ -108,7 +108,7 @@ func checkMigration(client clientset.Interface) error {
 
 	_, err = migration.Migrate(currentInstalledCoreDNSversion, kubeadmconstants.CoreDNSVersion, corefile, false)
 	if err != nil {
-		return err
+		return errors.Wrap(err, "CoreDNS will not be upgraded")
 	}
 	return nil
 }

cmd/kubeadm/app/util/apiclient/idempotency.go

@@ -147,6 +147,21 @@ func CreateOrUpdateDeployment(client clientset.Interface, deploy *apps.Deploymen
 	return nil
 }
 
+// CreateOrRetainDeployment creates a Deployment if the target resource doesn't exist. If the resource exists already, this function will retain the resource instead.
+func CreateOrRetainDeployment(client clientset.Interface, deploy *apps.Deployment, deployName string) error {
+	if _, err := client.AppsV1().Deployments(deploy.ObjectMeta.Namespace).Get(deployName, metav1.GetOptions{}); err != nil {
+		if !apierrors.IsNotFound(err) {
+			return nil
+		}
+		if _, err := client.AppsV1().Deployments(deploy.ObjectMeta.Namespace).Create(deploy); err != nil {
+			if !apierrors.IsAlreadyExists(err) {
+				return errors.Wrap(err, "unable to create deployment")
+			}
+		}
+	}
+	return nil
+}
+
 // CreateOrUpdateDaemonSet creates a DaemonSet if the target resource doesn't exist. If the resource exists already, this function will update the resource instead.
 func CreateOrUpdateDaemonSet(client clientset.Interface, ds *apps.DaemonSet) error {
 	if _, err := client.AppsV1().DaemonSets(ds.ObjectMeta.Namespace).Create(ds); err != nil {