From 05092f8389aeb7e95e9009a4fbca07fb62948582 Mon Sep 17 00:00:00 2001
From: Ole Markus With <o.with@sportradar.com>
Date: Sat, 30 Jan 2021 08:34:09 +0100
Subject: [PATCH] Add template function returning the latest image

Apply suggestions from code review

Co-authored-by: Peter Rifel <rifelpet@users.noreply.github.com>
---
 docs/operations/cluster_template.md      | 12 ++++++++----
 pkg/util/templater/BUILD.bazel           |  1 +
 pkg/util/templater/template_functions.go |  7 +++++++
 pkg/util/templater/templater_test.go     |  5 +++++
 4 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/docs/operations/cluster_template.md b/docs/operations/cluster_template.md
index bfc302c8cb..2dcbd81a5c 100644
--- a/docs/operations/cluster_template.md
+++ b/docs/operations/cluster_template.md
@@ -16,8 +16,8 @@ metadata:
   kops.k8s.io/cluster: {{ '{{.clusterName}}.{{.dnsZone}}' }}
   name: nodes
 spec:
-  image: coreos.com/CoreOS-stable-1409.6.0-hvm
-  kubernetesVersion: {{ '{{.kubernetesVersion}}' }}
+  image: {{ ChannelRecommendedImage .cloud .kubernetesVersion }}
+  kubernetesVersion: {{ '{{ ChannelRecommendedKubernetesUpgradeVersion .kubernetesVersion }}' }}
   machineType: m4.large
   maxPrice: "0.5"
   maxSize: 20
@@ -127,9 +127,13 @@ spec:
 
 This function returns the kubernetes version recommended for the running kops version.
 
-##### ChannelRecommendedKopsUpgradeVersion <kuberneteVersion>
+##### ChannelRecommendedKubernetesUpgradeVersion <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.
+This function returns the recommended kubernetes version given that you currently run `<kubernetesVersion>`. Typically this is the latest patch version supported by the given channel.
+
+##### ChannelRecommendedImage <cloudProvider> <kuberneteVersion>
+
+This function returns the recommended image for the given cloud provider and kubernetes version.
 
 #### Sprig functions
 
diff --git a/pkg/util/templater/BUILD.bazel b/pkg/util/templater/BUILD.bazel
index 87b96665be..58de4dd77c 100644
--- a/pkg/util/templater/BUILD.bazel
+++ b/pkg/util/templater/BUILD.bazel
@@ -13,6 +13,7 @@ go_library(
         "//pkg/apis/kops:go_default_library",
         "//pkg/apis/kops/util:go_default_library",
         "//vendor/github.com/Masterminds/sprig/v3:go_default_library",
+        "//vendor/github.com/blang/semver/v4:go_default_library",
     ],
 )
 
diff --git a/pkg/util/templater/template_functions.go b/pkg/util/templater/template_functions.go
index bac7fac431..2f9e2010e4 100644
--- a/pkg/util/templater/template_functions.go
+++ b/pkg/util/templater/template_functions.go
@@ -20,6 +20,7 @@ import (
 	"text/template"
 
 	"github.com/Masterminds/sprig/v3"
+	"github.com/blang/semver/v4"
 	"k8s.io/kops"
 	kopsapi "k8s.io/kops/pkg/apis/kops"
 	"k8s.io/kops/pkg/apis/kops/util"
@@ -62,5 +63,11 @@ func (r *Templater) templateFuncsMap(tm *template.Template) template.FuncMap {
 
 	}
 
+	funcs["ChannelRecommendedImage"] = func(cloud, k8sVersion string) string {
+		ver, _ := semver.ParseTolerant(k8sVersion)
+		imageSpec := r.channel.FindImage(kopsapi.CloudProviderID(cloud), ver)
+		return imageSpec.Name
+	}
+
 	return funcs
 }
diff --git a/pkg/util/templater/templater_test.go b/pkg/util/templater/templater_test.go
index f557cf0eaf..38663a3b6b 100644
--- a/pkg/util/templater/templater_test.go
+++ b/pkg/util/templater/templater_test.go
@@ -95,6 +95,11 @@ func TestRenderChannelFunctions(t *testing.T) {
 			Template: `{{ ChannelRecommendedKubernetesUpgradeVersion "1.4.2" }}`,
 			Expected: "1.4.8",
 		},
+		{
+			Context:  map[string]interface{}{},
+			Template: `{{ ChannelRecommendedImage "aws" "1.4.2" }}`,
+			Expected: "kope.io/k8s-1.4-debian-jessie-amd64-hvm-ebs-2016-10-21",
+		},
 	}
 	makeRenderTests(t, cases)
 }