Add template function for upgrade version

docs/operations/cluster_template.md

@@ -121,6 +121,18 @@ spec:
 
 ### Template Functions
 
+#### Kops specific functions
+
+##### ChannelRecommendedKopsKubernetesVersion
+
+This function returns the kubernetes version recommended for the running kops version.
+
+##### ChannelRecommendedKopsUpgradeVersion <kuberneteVersion>
+
+This function returns the kubernetes upgrade recommendation given that you run `<kubernetesVersion>`. Typically this is the latest minor version supported by the given channel.
+
+#### Sprig functions
+
 The entire set of https://github.com/Masterminds/sprig functions are available within the templates for you. Note if you want to use the 'defaults' functions switch off the verification check on the command line by `--fail-on-missing=false`;
 
 ```YAML

docs/releases/1.20-NOTES.md

@@ -4,6 +4,8 @@
 
 # Significant changes
 
+* Added [template funtions](https://kops.sigs.k8s.io/operations/cluster_template/#template-functions) for kubernetes version based on channel data.
+
 # Breaking changes
 
 * Support for Kubernetes 1.11 and 1.12 has been removed.
@@ -14,6 +16,8 @@
 
 # Required Actions
 
+* If you are running `kops toolbox template` in an airgapped environment, you have to set `--channel` to point to a local channel file.
+
 # Deprecations
 
 * Support for Kubernetes versions 1.13 and 1.14 are deprecated and will be removed in kOps 1.21.

pkg/util/templater/BUILD.bazel

@@ -11,6 +11,7 @@ go_library(
     deps = [
         "//:go_default_library",
         "//pkg/apis/kops:go_default_library",
+        "//pkg/apis/kops/util:go_default_library",
         "//vendor/github.com/Masterminds/sprig/v3:go_default_library",
     ],
 )

pkg/util/templater/template_functions.go

@@ -22,6 +22,7 @@ import (
 	"github.com/Masterminds/sprig/v3"
 	"k8s.io/kops"
 	kopsapi "k8s.io/kops/pkg/apis/kops"
+	"k8s.io/kops/pkg/apis/kops/util"
 )
 
 // templateFuncsMap returns a map if the template functions for this template
@@ -40,8 +41,25 @@ func (r *Templater) templateFuncsMap(tm *template.Template) template.FuncMap {
 		return content
 	}
 
-	funcs["ChannelRecommendedKubernetesVersion"] = func() string {
+	funcs["ChannelRecommendedKubernetesUpgradeVersion"] = func(version string) string {
+
+		parsed, err := util.ParseKubernetesVersion(version)
+		if err != nil {
+			panic(err.Error())
+		}
+
+		versionInfo := kopsapi.FindKubernetesVersionSpec(r.channel.Spec.KubernetesVersions, *parsed)
+		recommended, err := versionInfo.FindRecommendedUpgrade(*parsed)
+		if err != nil {
+			panic(err.Error())
+		}
+		return recommended.String()
+
+	}
+
+	funcs["ChannelRecommendedKopsKubernetesVersion"] = func() string {
 		return kopsapi.RecommendedKubernetesVersion(r.channel, kops.Version).String()
+
 	}
 
 	return funcs

pkg/util/templater/templater_test.go

@@ -18,6 +18,7 @@ package templater
 
 import (
 	"io/ioutil"
+	"os"
 	"testing"
 
 	"k8s.io/kops/pkg/diff"
@@ -86,9 +87,14 @@ func TestRenderChannelFunctions(t *testing.T) {
 	cases := []renderTest{
 		{
 			Context:  map[string]interface{}{},
-			Template: `{{ ChannelRecommendedKubernetesVersion }}`,
+			Template: `{{ ChannelRecommendedKopsKubernetesVersion }}`,
 			Expected: "1.5.2",
 		},
+		{
+			Context:  map[string]interface{}{},
+			Template: `{{ ChannelRecommendedKubernetesUpgradeVersion "1.4.2" }}`,
+			Expected: "1.4.8",
+		},
 	}
 	makeRenderTests(t, cases)
 }
@@ -194,9 +200,13 @@ type renderTest struct {
 }
 
 func makeRenderTests(t *testing.T, tests []renderTest) {
-	channel, err := simple.NewMockChannel()
+
+	sourcePath := "../../../tests/integration/channel/simple/channel.yaml"
+	s, _ := os.Getwd()
+
+	channel, err := simple.NewMockChannel(sourcePath)
 	if err != nil {
-		t.Fatalf("could not load channel: %v", err)
+		t.Fatalf("could not load channel: %v, %s", err, s)
 	}
 	r := NewTemplater(channel)
 	for i, x := range tests {

tests/integration/channel/integration_test.go

@@ -28,8 +28,9 @@ import (
 
 // TestKopsUpgrades tests the version logic for kops versions
 func TestKopsUpgrades(t *testing.T) {
+	sourcePath := "simple/channel.yaml"
 
-	channel, err := simple.NewMockChannel()
+	channel, err := simple.NewMockChannel(sourcePath)
 	if err != nil {
 		t.Fatalf("failed to create channel: %v", err)
 	}

tests/integration/channel/simple/mock_channel.go

@@ -23,8 +23,7 @@ import (
 	"k8s.io/kops/pkg/apis/kops"
 )
 
-func NewMockChannel() (*kops.Channel, error) {
+func NewMockChannel(sourcePath string) (*kops.Channel, error) {
-	sourcePath := "simple/channel.yaml"
 	sourceBytes, err := ioutil.ReadFile(sourcePath)
 	if err != nil {
 		return nil, fmt.Errorf("unexpected error reading sourcePath %q: %v", sourcePath, err)