[Feature] CoreDNS: Allow for Specification of external CoreFile

Allow users to provide entirely custom CoreFile for CoreDNS to provide improved flexibility.

docs/cluster_spec.md

@@ -458,6 +458,39 @@ Specifying KubeDNS will install kube-dns as the default service discovery.
 
 This will install [CoreDNS](https://coredns.io/) instead of kube-dns.
 
+If you are using CoreDNS and want to use an entirely custom CoreFile you can do this by specifying the file. This will not work with any other options which interact with the default CoreFile.
+
+```yaml
+spec:
+  kubeDNS:
+    provider: CoreDNS
+    ExternalCoreFile: |
+      amazonaws.com:53 {
+            errors
+            log . {
+                class denial error
+            }
+            health :8084
+            prometheus :9153
+            proxy . 169.254.169.253 {
+            }
+            cache 30
+        }
+        .:53 {
+            errors
+            health :8080
+            autopath @kubernetes
+            kubernetes cluster.local {
+                pods verified
+                upstream 169.254.169.253
+                fallthrough in-addr.arpa ip6.arpa
+            }
+            prometheus :9153
+            proxy . 169.254.169.253
+            cache 300
+        }
+```
+
 **Note:** If you are upgrading to CoreDNS, kube-dns will be left in place and must be removed manually (you can scale the kube-dns and kube-dns-autoscaler deployments in the `kube-system` namespace to 0 as a starting point). The `kube-dns` Service itself should be left in place, as this retains the ClusterIP and eliminates the possibility of DNS outages in your cluster. If you would like to continue autoscaling, update the `kube-dns-autoscaler` Deployment container command for `--target=Deployment/kube-dns` to be `--target=Deployment/coredns`.
 
 ### kubeControllerManager

pkg/apis/kops/cluster.go

@@ -356,6 +356,8 @@ type KubeDNSConfig struct {
 	CacheMaxConcurrent int `json:"cacheMaxConcurrent,omitempty"`
 	// Domain is the dns domain
 	Domain string `json:"domain,omitempty"`
+	// ExternalCoreFile is used to provide a complete CoreDNS CoreFile by the user - ignores other provided flags which modify the CoreFile.
+	ExternalCoreFile string `json:"externalCoreFile,omitempty"`
 	// Image is the name of the docker image to run - @deprecated as this is now in the addon
 	Image string `json:"image,omitempty"`
 	// Replicas is the number of pod replicas - @deprecated as this is now in the addon and controlled by autoscaler

pkg/apis/kops/v1alpha1/cluster.go

@@ -355,6 +355,8 @@ type KubeDNSConfig struct {
 	CacheMaxConcurrent int `json:"cacheMaxConcurrent,omitempty"`
 	// Domain is the dns domain
 	Domain string `json:"domain,omitempty"`
+	// ExternalCoreFile is used to provide a complete CoreDNS CoreFile by the user - ignores other provided flags which modify the CoreFile.
+	ExternalCoreFile string `json:"externalCoreFile,omitempty"`
 	// Image is the name of the docker image to run - @deprecated as this is now in the addon
 	Image string `json:"image,omitempty"`
 	// Replicas is the number of pod replicas - @deprecated as this is now in the addon, and controlled by autoscaler

pkg/apis/kops/v1alpha2/cluster.go

@@ -356,6 +356,8 @@ type KubeDNSConfig struct {
 	CacheMaxConcurrent int `json:"cacheMaxConcurrent,omitempty"`
 	// Domain is the dns domain
 	Domain string `json:"domain,omitempty"`
+	// ExternalCoreFile is used to provide a complete CoreDNS CoreFile by the user - ignores other provided flags which modify the CoreFile.
+	ExternalCoreFile string `json:"externalCoreFile,omitempty"`
 	// Image is the name of the docker image to run - @deprecated as this is now in the addon
 	Image string `json:"image,omitempty"`
 	// Replicas is the number of pod replicas - @deprecated as this is now in the addon, and controlled by autoscaler

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

@@ -59,6 +59,9 @@ metadata:
       addonmanager.kubernetes.io/mode: EnsureExists
 data:
   Corefile: |
+  {{- if KubeDNS.ExternalCoreFile }}
+    {{ KubeDNS.ExternalCoreFile }}
+  {{- else }}
     .:53 {
         errors
         health
@@ -74,6 +77,7 @@ data:
         loadbalance
         reload
     }
+  {{- end }}
 ---
 apiVersion: apps/v1
 kind: Deployment

upup/models/cloudup/resources/addons/coredns.addons.k8s.io/k8s-1.6.yaml.template

@@ -59,6 +59,9 @@ metadata:
       addonmanager.kubernetes.io/mode: EnsureExists
 data:
   Corefile: |
+  {{- if KubeDNS.ExternalCoreFile }}
+    {{ KubeDNS.ExternalCoreFile }}
+  {{- else }}
     .:53 {
         errors
         health
@@ -74,6 +77,7 @@ data:
         loadbalance
         reload
     }
+  {{- end }}
 ---
 apiVersion: apps/v1
 kind: Deployment

upup/pkg/fi/cloudup/bootstrapchannelbuilder.go

@@ -264,7 +264,7 @@ func (b *BootstrapChannelBuilder) buildAddons() *channelsapi.Addons {
 	if kubeDNS.Provider == "CoreDNS" {
 		{
 			key := "coredns.addons.k8s.io"
-			version := "1.3.1-kops.3"
+			version := "1.3.1-kops.4"
 
 			{
 				location := key + "/k8s-1.6.yaml"
@@ -283,7 +283,7 @@ func (b *BootstrapChannelBuilder) buildAddons() *channelsapi.Addons {
 
 		{
 			key := "coredns.addons.k8s.io"
-			version := "1.3.0-kops.2"
+			version := "1.3.0-kops.3"
 
 			{
 				location := key + "/k8s-1.12.yaml"