implicitly handle load balancers

This preserves load balancers as being part of the node lists,
but makes it possible to handle the case where the user
did not provide a LB in the config.

The LB is added in the derived config.

Includes minor cleanup in types.go and validate.go.

pkg/cluster/config/v1alpha2/types.go

@@ -28,7 +28,7 @@ type Config struct {
 	// TypeMeta representing the type of the object and its API schema version.
 	metav1.TypeMeta `json:",inline"`
 
-	// nodes constains the list of nodes defined in the `kind` Config
+	// Nodes constains the list of nodes defined in the `kind` Config
 	Nodes []Node `json:"nodes"`
 }
 
@@ -39,7 +39,7 @@ type Node struct {
 	// Replicas is the number of desired node replicas.
 	// Defaults to 1
 	Replicas *int32 `json:"replicas,omitempty"`
-	// Role defines the role of the nodw in the in the Kubernetes cluster managed by `kind`
+	// Role defines the role of the node in the in the Kubernetes cluster managed by `kind`
 	// Defaults to "control-plane"
 	Role NodeRole `json:"role,omitempty"`
 	// Image is the node image to use when running the cluster
@@ -70,7 +70,7 @@ const (
 	ExternalEtcdRole NodeRole = "external-etcd"
 	// ExternalLoadBalancerRole identifies a node that hosts an external load balancer for API server
 	// in HA configurations.
-	// WARNING: this node type is not yet implemented!
-	// Please note that `kind` nodes hosting external load balancer are not kubernetes nodes
+	// If multiple control-plane nodes exists, a node with this role will be added automatically if missing.
+	// Please note that `kind` nodes hosting external load balancer are not Kubernetes nodes.
 	ExternalLoadBalancerRole NodeRole = "external-load-balancer"
 )

pkg/cluster/config/validate.go

@@ -30,7 +30,7 @@ func (c *Config) Validate() error {
 	// All nodes in the config should be valid
 	for i, n := range c.Nodes {
 		if err := n.Validate(); err != nil {
-			errs = append(errs, errors.Errorf("invalid configuration for node %d", i))
+			errs = append(errs, errors.Errorf("invalid configuration for node %d: %v", i, err))
 		}
 	}
 

pkg/cluster/internal/create/derivedconfig.go

@@ -24,6 +24,7 @@ import (
 	"sigs.k8s.io/kind/pkg/util"
 
 	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
 )
 
 // DerivedConfig contains config-like data computed from pkg/cluster/config.Config
@@ -141,6 +142,16 @@ func Derive(c *config.Config) (*DerivedConfig, error) {
 		}
 	}
 
+	// Add a load balancer automatically if one does not exists already and if the number
+	// of control plane nodes is more than one
+	if d.ExternalLoadBalancer() == nil && len(d.ControlPlanes()) > 1 {
+		n := config.Node{
+			Role:  config.ExternalLoadBalancerRole,
+			Image: d.BootStrapControlPlane().Image, // should always return non-nil in this branch
+		}
+		log.Info("Automatically creating a load balancer node")
+		d.Add(&n)
+	}
 	return d, nil
 }