Add docs and demo for imageTags

docs/kustomization.yaml

@@ -184,3 +184,19 @@ vars:
       apiVersion: apps/v1
     fieldref:
       fieldpath: spec.template.spec.restartPolicy
+
+# ImageTags modify the tags for images without creating patches.
+# E.g. Given this fragment of a Deployment:
+# ```
+#  containers:
+#    - name: myapp
+#      image: mycontainerregistry/myimage:v0
+#    - name: nginxapp
+#      image: nginx:1.7.9
+#```
+# one can change the tag of myimage to v1 and the tag of nginx to 1.8.0 with the following:
+imageTags:
+  - name: mycontainerregistry/myimage
+    newTag: v1
+  - name: nginx
+    newTag: 1.8.0

examples/README.md

@@ -31,3 +31,5 @@ go get github.com/kubernetes-sigs/kustomize
    Alice and Bob.
 
  * [container args](wordpress/README.md) - Injecting k8s runtime data into container arguments (e.g. to point wordpress to a SQL service).
+
+ * [image tags](imageTags.md) - Updating image tags without applying a patch.

examples/imageTags.md

@@ -0,0 +1,75 @@
+# Demo: change image tags
+
+
+Define a place to work:
+
+<!-- @makeWorkplace @test -->
+```
+DEMO_HOME=$(mktemp -d)
+```
+
+Make a `kustomization` containing a pod resource
+
+<!-- @createKustomization @test -->
+```
+cat <<EOF >$DEMO_HOME/kustomization.yaml
+resources:
+- pod.yaml
+EOF
+```
+
+Declare the pod resource
+
+<!-- @createDeployment @test -->
+```
+cat <<EOF >$DEMO_HOME/pod.yaml
+apiVersion: v1
+kind: Pod
+metadata:
+  name: myapp-pod
+  labels:
+    app: myapp
+spec:
+  containers:
+  - name: myapp-container
+    image: busybox:1.29.0
+    command: ['sh', '-c', 'echo The app is running! && sleep 3600']
+  initContainers:
+  - name: init-mydb
+    image: busybox:1.29.0
+    command: ['sh', '-c', 'until nslookup mydb; do echo waiting for mydb; sleep 2; done;']
+EOF
+```
+
+The `myapp-pod` resource declares an initContainer and a container, both use the image `busybox:1.29.0`.
+The tag `1.29.0` can be changed by adding `imageTags` in `kustomization.yaml`.
+
+
+Add `imageTags`:
+<!-- @addImageTags @test -->
+```
+cd $DEMO_HOME
+kustomize edit set imagetag busybox:1.29.1
+```
+
+The `kustomization.yaml` will be added following `imageTags`.
+> ```
+> imageTags:
+> - name: busybox
+>   newTag: 1.29.1
+> ```
+
+Now build this `kustomization`
+<!-- @kustomizeBuild @test -->
+```
+kustomize build $DEMO_HOME
+```
+
+Confirm that this replaces _both_ busybox tags:
+
+<!-- @confirmTags @test -->
+```
+test 2 == \
+  $(kustomize build $DEMO_HOME | grep busybox:1.29.1 | wc -l); \
+  echo $?
+```