Improve behaviour of --node{-(min|max)}

- update help messages
- bail when --nodes is above --nodes-max
- set --nodes when --nodes-min and --nodes-max are given and it is
  outside the ragne
- print a message when --nodes is default, but --nodes-min as well
  as --nodes-max are set

pkg/cfn/builder/nodegroup.go

@@ -6,6 +6,8 @@ import (
 	cfn "github.com/aws/aws-sdk-go/service/cloudformation"
 	gfn "github.com/awslabs/goformation/cloudformation"
 
+	"github.com/kubicorn/kubicorn/pkg/logger"
+
 	"github.com/weaveworks/eksctl/pkg/eks/api"
 
 	"github.com/weaveworks/eksctl/pkg/nodebootstrap"
@@ -51,9 +53,25 @@ func (n *NodeGroupResourceSet) AddAllResources() error {
 	}
 	n.userData = gfn.NewString(userData)
 
-	if n.spec.MinSize == 0 && n.spec.MaxSize == 0 {
+	switch {
+	case n.spec.MinSize == 0 && n.spec.MaxSize == 0:
 		n.spec.MinSize = n.spec.DesiredCapacity
 		n.spec.MaxSize = n.spec.DesiredCapacity
+	case n.spec.MinSize > 0 && n.spec.MaxSize > 0:
+		if n.spec.DesiredCapacity == api.DefaultNodeCount {
+			msgPrefix := fmt.Sprintf("as --nodes-min=%d and --nodes-max=%d were given", n.spec.MinSize, n.spec.MaxSize)
+			if n.spec.DesiredCapacity < n.spec.MinSize {
+				n.spec.DesiredCapacity = n.spec.MaxSize
+				logger.Info("%s, --nodes=%d was set automatically as default value (--node=%d) was outside the set renge",
+					msgPrefix, n.spec.DesiredCapacity, api.DefaultNodeCount)
+			} else {
+				logger.Info("%s, default value of --nodes=%d was kept as it is within the set range",
+					msgPrefix, n.spec.DesiredCapacity)
+			}
+		}
+		if n.spec.DesiredCapacity > n.spec.MaxSize {
+			return fmt.Errorf("cannot use --nodes-max=%d and --nodes=%d at the same time", n.spec.MaxSize, n.spec.DesiredCapacity)
+		}
 	}
 
 	n.addResourcesForIAM()

pkg/ctl/create/cluster.go

@@ -57,11 +57,11 @@ func createClusterCmd() *cobra.Command {
 	fs.StringToStringVarP(&cfg.Tags, "tags", "", map[string]string{}, `A list of KV pairs used to tag the AWS resources (e.g. "Owner=John Doe,Team=Some Team")`)
 
 	fs.StringVarP(&ng.InstanceType, "node-type", "t", defaultNodeType, "node instance type")
-	fs.IntVarP(&ng.DesiredCapacity, "nodes", "N", api.DefaultNodeCount, "total number of nodes (for a static ASG)")
+	fs.IntVarP(&ng.DesiredCapacity, "nodes", "N", api.DefaultNodeCount, "total number of nodes (desired capacity of AGS)")
 
 	// TODO: https://github.com/weaveworks/eksctl/issues/28
-	fs.IntVarP(&ng.MinSize, "nodes-min", "m", 0, "minimum nodes in ASG")
-	fs.IntVarP(&ng.MaxSize, "nodes-max", "M", 0, "maximum nodes in ASG")
+	fs.IntVarP(&ng.MinSize, "nodes-min", "m", 0, "minimum nodes in ASG (leave unset for a static nodegroup)")
+	fs.IntVarP(&ng.MaxSize, "nodes-max", "M", 0, "maximum nodes in ASG (leave unset for a static nodegroup)")
 
 	fs.IntVarP(&ng.VolumeSize, "node-volume-size", "", 0, "Node volume size (in GB)")
 	fs.IntVar(&ng.MaxPodsPerNode, "max-pods-per-node", 0, "maximum number of pods per node (set automatically if unspecified)")