Add set-default-labels function

Author: yuwenma

examples/set-default-labels-nested-package/.expected/diff.patch

@@ -0,0 +1,24 @@
+diff --git a/resources.yaml b/resources.yaml
+index 1e641f7..bb4be90 100644
+--- a/resources.yaml
++++ b/resources.yaml
+@@ -2,6 +2,9 @@ apiVersion: v1
+ kind: ConfigMap
+ metadata:
+   name: the-map
++  labels:
++    color: orange
++    fruit: apple
+ data:
+   some-key: some-value
+ ---
+@@ -10,6 +13,9 @@ kind: MyResource
+ metadata:
+   name: the-service
+   namespace: the-namespace
++  labels:
++    color: orange
++    fruit: apple
+ spec:
+   selector:
+     labels:

examples/set-default-labels-nested-package/.krmignore

@@ -0,0 +1 @@
+.expected

examples/set-default-labels-nested-package/Kptfile

@@ -0,0 +1,9 @@
+apiVersion: kpt.dev/v1
+kind: Kptfile
+metadata:
+  name: root-app
+  annotations:
+    config.kubernetes.io/local-config: "true"
+pipeline:
+  mutators:
+    - image: gcr.io/kpt-fn/set-default-labels:unstable

examples/set-default-labels-nested-package/README.md

@@ -0,0 +1,38 @@
+# set-default-labels: Nested Package Example
+
+### Overview
+
+This example shows how to run [`set-default-labels`] in a nested KPT package. 
+
+### Fetch the example package
+
+Get the example package by running the following commands:
+
+```shell
+kpt pkg get https://github.com/GoogleContainerTools/kpt-functions-catalog.git/examples/set-default-labels-nested-package your-app
+```
+
+We use the following `Kptfile` to configure the function.
+
+```yaml
+apiVersion: kpt.dev/v1
+kind: Kptfile
+metadata:
+  name: your-app
+pipeline:
+  mutators:
+    - image: gcr.io/kpt-fn/set-default-labels:unstable
+```
+
+### Function invocation
+
+Invoke the function by running the following commands:
+
+```shell
+$ kpt fn render your-app
+```
+
+### Expected result
+All resources should have `app.kubernetes.io/name: your-app` label added to the meta and label selector fields.
+
+[`set-default-labels`]: https://catalog.kpt.dev/set-labels/v0.1/

examples/set-default-labels-nested-package/app1_ghost/Kptfile

@@ -0,0 +1,8 @@
+apiVersion: kpt.dev/v1
+kind: Kptfile
+metadata:
+  name: app1_ghost
+  annotations:
+    config.kubernetes.io/local-config: "true"
+info:
+  description: sample description

examples/set-default-labels-nested-package/app1_ghost/resources.yaml

@@ -0,0 +1,18 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: ghost
+spec:
+  replicas: 2
+  template:
+    spec:
+      containers:
+        - name: ghost
+          image: ghost:3-alpine
+          ports:
+            - containerPort: 2368
+          env:
+            - name: url
+              value: http://localhost:8080
+            - name: database__connection__database
+              value: ghost

examples/set-default-labels-nested-package/app2_mysql/Kptfile

@@ -0,0 +1,8 @@
+apiVersion: kpt.dev/v1
+kind: Kptfile
+metadata:
+  name: app2_mysql
+  annotations:
+    config.kubernetes.io/local-config: "true"
+info:
+  description: sample description

examples/set-default-labels-nested-package/app2_mysql/README.md

@@ -0,0 +1,21 @@
+# app2
+
+## Description
+sample description
+
+## Usage
+
+### Fetch the package
+`kpt pkg get REPO_URI[.git]/PKG_PATH[@VERSION] app2`
+Details: https://kpt.dev/reference/cli/pkg/get/
+
+### View package content
+`kpt pkg tree app2`
+Details: https://kpt.dev/reference/cli/pkg/tree/
+
+### Apply the package
+```
+kpt live init app2
+kpt live apply app2 --reconcile-timeout=2m --output=table
+```
+Details: https://kpt.dev/reference/cli/live/

examples/set-default-labels-nested-package/app2_mysql/resources.yaml

@@ -0,0 +1,15 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: mysql
+spec:
+  template:
+    spec:
+      containers:
+        - name: mysql
+          image: mysql:5.7
+          ports:
+            - name: mysql
+              containerPort: 3306
+  strategy:
+    type: Recreate

functions/go/Makefile

@@ -37,6 +37,7 @@ FUNCTIONS := \
 	set-enforcement-action \
 	set-image \
 	set-labels \
+	set-default-labels \
 	set-namespace \
 	set-project-id \
 	source-gcloud-config \