kubeadm: add configuration option to not taint master

Although tainting the master is normally a good and proper thing to do in some
situations (docker for mac in our case, but I suppose minikube and such as
well) having a single host configuration is desirable.

In linuxkit we have a [workaround](443e47c408/projects/kubernetes/kubernetes/kubeadm-init.sh (L19...L22))
to remove the taint after initialisation. With the change here we could simply
populate /etc/kubeadm/kubeadm.yaml` with `noTaintMaster: true` instead and have
it never be tainted in the first place.

I have only added this to the config file and not to the CLI since AIUI the
latter is somewhat deprecated.

The code also arranges to _remove_ an existing taint if it is unwanted. I'm
unsure if this behaviour is correct or desirable, I think a reasonable argument
could be made for leaving an existing taint in place too.

Signed-off-by: Ian Campbell <ijc@docker.com>

cmd/kubeadm/app/apis/kubeadm/types.go

@@ -50,6 +50,10 @@ type MasterConfiguration struct {
 	// If not specified, defaults to Node and RBAC, meaning both the node
 	// authorizer and RBAC are enabled.
 	AuthorizationModes []string
+	// NoTaintMaster will, if set, suppress the tainting of the
+	// master node allowing workloads to be run on it (e.g. in
+	// single node configurations).
+	NoTaintMaster bool
 
 	// Mark the controller and api server pods as privileged as some cloud
 	// controllers like openstack need escalated privileges under some conditions

cmd/kubeadm/app/apis/kubeadm/v1alpha1/types.go

@@ -50,6 +50,10 @@ type MasterConfiguration struct {
 	// If not specified, defaults to Node and RBAC, meaning both the node
 	// authorizer and RBAC are enabled.
 	AuthorizationModes []string `json:"authorizationModes,omitempty"`
+	// NoTaintMaster will, if set, suppress the tainting of the
+	// master node allowing workloads to be run on it (e.g. in
+	// single node configurations).
+	NoTaintMaster bool `json:"noTaintMaster,omitempty"`
 
 	// Mark the controller and api server pods as privileged as some cloud
 	// controllers like openstack need escalated privileges under some conditions

cmd/kubeadm/app/apis/kubeadm/v1alpha1/zz_generated.conversion.go

@@ -202,6 +202,7 @@ func autoConvert_v1alpha1_MasterConfiguration_To_kubeadm_MasterConfiguration(in
 	out.CloudProvider = in.CloudProvider
 	out.NodeName = in.NodeName
 	out.AuthorizationModes = *(*[]string)(unsafe.Pointer(&in.AuthorizationModes))
+	out.NoTaintMaster = in.NoTaintMaster
 	out.PrivilegedPods = in.PrivilegedPods
 	out.Token = in.Token
 	out.TokenTTL = (*v1.Duration)(unsafe.Pointer(in.TokenTTL))
@@ -244,6 +245,7 @@ func autoConvert_kubeadm_MasterConfiguration_To_v1alpha1_MasterConfiguration(in
 	out.CloudProvider = in.CloudProvider
 	out.NodeName = in.NodeName
 	out.AuthorizationModes = *(*[]string)(unsafe.Pointer(&in.AuthorizationModes))
+	out.NoTaintMaster = in.NoTaintMaster
 	out.PrivilegedPods = in.PrivilegedPods
 	out.Token = in.Token
 	out.TokenTTL = (*v1.Duration)(unsafe.Pointer(in.TokenTTL))

cmd/kubeadm/app/cmd/init.go

@@ -388,7 +388,7 @@ func (i *Init) Run(out io.Writer) error {
 	}
 
 	// PHASE 4: Mark the master with the right label/taint
-	if err := markmasterphase.MarkMaster(client, i.cfg.NodeName); err != nil {
+	if err := markmasterphase.MarkMaster(client, i.cfg.NodeName, !i.cfg.NoTaintMaster); err != nil {
 		return fmt.Errorf("error marking master: %v", err)
 	}
 

cmd/kubeadm/app/cmd/phases/markmaster.go

@@ -75,7 +75,7 @@ func NewCmdMarkMaster() *cobra.Command {
 			client, err := kubeconfigutil.ClientSetFromFile(kubeConfigFile)
 			kubeadmutil.CheckErr(err)
 
-			err = markmasterphase.MarkMaster(client, internalcfg.NodeName)
+			err = markmasterphase.MarkMaster(client, internalcfg.NodeName, !internalcfg.NoTaintMaster)
 			kubeadmutil.CheckErr(err)
 		},
 	}

cmd/kubeadm/app/phases/markmaster/markmaster.go

@@ -32,9 +32,13 @@ import (
 )
 
 // MarkMaster taints the master and sets the master label
-func MarkMaster(client clientset.Interface, masterName string) error {
+func MarkMaster(client clientset.Interface, masterName string, taint bool) error {
 
+	if taint {
 		fmt.Printf("[markmaster] Will mark node %s as master by adding a label and a taint\n", masterName)
+	} else {
+		fmt.Printf("[markmaster] Will mark node %s as master by adding a label\n", masterName)
+	}
 
 	// Loop on every falsy return. Return with an error if raised. Exit successfully if true is returned.
 	return wait.Poll(kubeadmconstants.APICallRetryInterval, kubeadmconstants.MarkMasterTimeout, func() (bool, error) {
@@ -56,7 +60,7 @@ func MarkMaster(client clientset.Interface, masterName string) error {
 		}
 
 		// The master node should be tainted and labelled accordingly
-		markMasterNode(n)
+		markMasterNode(n, taint)
 
 		newData, err := json.Marshal(n)
 		if err != nil {
@@ -76,15 +80,23 @@ func MarkMaster(client clientset.Interface, masterName string) error {
 			return false, err
 		}
 
+		if taint {
 			fmt.Printf("[markmaster] Master %s tainted and labelled with key/value: %s=%q\n", masterName, kubeadmconstants.LabelNodeRoleMaster, "")
+		} else {
+			fmt.Printf("[markmaster] Master %s labelled with key/value: %s=%q\n", masterName, kubeadmconstants.LabelNodeRoleMaster, "")
+		}
 
 		return true, nil
 	})
 }
 
-func markMasterNode(n *v1.Node) {
+func markMasterNode(n *v1.Node, taint bool) {
 	n.ObjectMeta.Labels[kubeadmconstants.LabelNodeRoleMaster] = ""
+	if taint {
 		addTaintIfNotExists(n, kubeadmconstants.MasterTaint)
+	} else {
+		delTaintIfExists(n, kubeadmconstants.MasterTaint)
+	}
 }
 
 func addTaintIfNotExists(n *v1.Node, t v1.Taint) {
@@ -96,3 +108,14 @@ func addTaintIfNotExists(n *v1.Node, t v1.Taint) {
 
 	n.Spec.Taints = append(n.Spec.Taints, t)
 }
+
+func delTaintIfExists(n *v1.Node, t v1.Taint) {
+	var taints []v1.Taint
+	for _, taint := range n.Spec.Taints {
+		if taint == t {
+			continue
+		}
+		taints = append(taints, t)
+	}
+	n.Spec.Taints = taints
+}

cmd/kubeadm/app/phases/markmaster/markmaster_test.go

@@ -43,32 +43,51 @@ func TestMarkMaster(t *testing.T) {
 		name          string
 		existingLabel string
 		existingTaint *v1.Taint
+		wantTaint     bool
 		expectedPatch string
 	}{
 		{
 			"master label and taint missing",
 			"",
 			nil,
+			true,
 			"{\"metadata\":{\"labels\":{\"node-role.kubernetes.io/master\":\"\"}},\"spec\":{\"taints\":[{\"effect\":\"NoSchedule\",\"key\":\"node-role.kubernetes.io/master\"}]}}",
 		},
+		{
+			"master label and taint missing but taint not wanted",
+			"",
+			nil,
+			false,
+			"{\"metadata\":{\"labels\":{\"node-role.kubernetes.io/master\":\"\"}}}",
+		},
 		{
 			"master label missing",
 			"",
 			&kubeadmconstants.MasterTaint,
+			true,
 			"{\"metadata\":{\"labels\":{\"node-role.kubernetes.io/master\":\"\"}}}",
 		},
 		{
 			"master taint missing",
 			kubeadmconstants.LabelNodeRoleMaster,
 			nil,
+			true,
 			"{\"spec\":{\"taints\":[{\"effect\":\"NoSchedule\",\"key\":\"node-role.kubernetes.io/master\"}]}}",
 		},
 		{
 			"nothing missing",
 			kubeadmconstants.LabelNodeRoleMaster,
 			&kubeadmconstants.MasterTaint,
+			true,
 			"{}",
 		},
+		{
+			"nothing missing but taint unwanted",
+			kubeadmconstants.LabelNodeRoleMaster,
+			&kubeadmconstants.MasterTaint,
+			false,
+			"{\"spec\":{\"taints\":null}}",
+		},
 	}
 
 	for _, tc := range tests {
@@ -125,7 +144,7 @@ func TestMarkMaster(t *testing.T) {
 			t.Fatalf("MarkMaster(%s): unexpected error building clientset: %v", tc.name, err)
 		}
 
-		err = MarkMaster(cs, hostname)
+		err = MarkMaster(cs, hostname, tc.wantTaint)
 		if err != nil {
 			t.Errorf("MarkMaster(%s) returned unexpected error: %v", tc.name, err)
 		}