Allow running with 0 worker nodes

Author: hakman

pkg/apis/kops/validation/legacy.go

@@ -274,10 +274,6 @@ func DeepValidate(c *kops.Cluster, groups []*kops.InstanceGroup, strict bool, vf
 		return fmt.Errorf("must configure at least one ControlPlane InstanceGroup")
 	}
 
-	if nodeGroupCount == 0 {
-		return fmt.Errorf("must configure at least one Node InstanceGroup")
-	}
-
 	for _, g := range groups {
 		errs := CrossValidateInstanceGroup(g, c, cloud, strict)
 

upup/models/cloudup/resources/addons/coredns.addons.k8s.io/k8s-1.12.yaml.template

@@ -138,7 +138,7 @@ spec:
         - key: "CriticalAddonsOnly"
           operator: "Exists"
         {{- end }}
-        {{- if KarpenterEnabled }}
+        {{- if or IsControlPlaneOnly KarpenterEnabled }}
         - key: node-role.kubernetes.io/master
           operator: Exists
         - key: node-role.kubernetes.io/control-plane

upup/pkg/fi/cloudup/deepvalidate_test.go

@@ -44,7 +44,10 @@ func TestDeepValidate_NoNodeZones(t *testing.T) {
 	c := buildDefaultCluster(t)
 	var groups []*kopsapi.InstanceGroup
 	groups = append(groups, buildMinimalMasterInstanceGroup("subnet-us-test-1a"))
-	expectErrorFromDeepValidate(t, c, groups, "must configure at least one Node InstanceGroup")
+	err := validation.DeepValidate(c, groups, true, vfs.Context, nil)
+	if err != nil {
+		t.Fatalf("Expected no error from DeepValidate, got %v", err)
+	}
 }
 
 func TestDeepValidate_NoMasterZones(t *testing.T) {

upup/pkg/fi/cloudup/new_cluster.go

@@ -176,6 +176,7 @@ func (o *NewClusterOptions) InitDefaults() {
 	o.AdminAccess = []string{"0.0.0.0/0", "::/0"}
 	o.EtcdClusters = []string{"main", "events"}
 	o.Networking = "cilium"
+	o.NodeCount = 1
 	o.InstanceManager = "cloudgroups"
 
 	// Azure-specific
@@ -416,26 +417,27 @@ func NewCluster(opt *NewClusterOptions, clientset simple.Clientset) (*NewCluster
 	}
 
 	var nodes []*api.InstanceGroup
-
-	switch opt.InstanceManager {
-	case "karpenter":
-		if opt.DiscoveryStore == "" {
-			return nil, fmt.Errorf("karpenter requires --discovery-store")
-		}
-		cluster.Spec.Karpenter = &api.KarpenterConfig{
-			Enabled: true,
-		}
-		nodes, err = setupKarpenterNodes(cluster)
-		if err != nil {
-			return nil, err
-		}
-	case "cloudgroups":
-		nodes, err = setupNodes(opt, cluster, zoneToSubnetsMap)
-		if err != nil {
-			return nil, err
+	if opt.NodeCount > 0 {
+		switch opt.InstanceManager {
+		case "karpenter":
+			if opt.DiscoveryStore == "" {
+				return nil, fmt.Errorf("karpenter requires --discovery-store")
+			}
+			cluster.Spec.Karpenter = &api.KarpenterConfig{
+				Enabled: true,
+			}
+			nodes, err = setupKarpenterNodes(cluster)
+			if err != nil {
+				return nil, err
+			}
+		case "cloudgroups":
+			nodes, err = setupNodes(opt, cluster, zoneToSubnetsMap)
+			if err != nil {
+				return nil, err
+			}
+		default:
+			return nil, fmt.Errorf("invalid value %q for --instance-manager", opt.InstanceManager)
 		}
-	default:
-		return nil, fmt.Errorf("invalid value %q for --instance-manager", opt.InstanceManager)
 	}
 
 	apiservers, err := setupAPIServers(opt, cluster, zoneToSubnetsMap)
@@ -1080,7 +1082,7 @@ func setupNodes(opt *NewClusterOptions, cluster *api.Cluster, zoneToSubnetsMap m
 	// We then divvy up amongst the zones
 	numZones := len(opt.Zones)
 	nodeCount := opt.NodeCount
-	if nodeCount == 0 {
+	if nodeCount == 1 {
 		// If node count is not specified, default to the number of zones
 		nodeCount = int32(numZones)
 	}

upup/pkg/fi/cloudup/template_functions.go

@@ -399,6 +399,8 @@ func (tf *TemplateFunctions) AddTo(dest template.FuncMap, secretStore fi.SecretS
 
 	dest["ParseTaint"] = util.ParseTaint
 
+	dest["IsControlPlaneOnly"] = tf.IsControlPlaneOnly
+
 	dest["KarpenterEnabled"] = func() bool {
 		return cluster.Spec.Karpenter != nil && cluster.Spec.Karpenter.Enabled
 	}
@@ -511,6 +513,22 @@ func (tf *TemplateFunctions) HasHighlyAvailableControlPlane() bool {
 	return false
 }
 
+// IsControlPlaneOnly returns true if the cluster has only control plane node(s). False otherwise.
+func (tf *TemplateFunctions) IsControlPlaneOnly() bool {
+	var cp, wn int
+	for _, ig := range tf.InstanceGroups {
+		switch ig.Spec.Role {
+		case kops.InstanceGroupRoleControlPlane:
+			cp++
+		case kops.InstanceGroupRoleNode:
+			wn++
+		default:
+			// Ignore Bastion and APIServer
+		}
+	}
+	return cp > 0 && wn == 0
+}
+
 // CloudControllerConfigArgv returns the args to external cloud controller
 func (tf *TemplateFunctions) CloudControllerConfigArgv() ([]string, error) {
 	cluster := tf.Cluster