Add the mergeStrategy option to resource patching (#1269)

* This adds the ability to pass a mergeStrategy to a patch resource.
  this is valuable because the default merge strategy for kubernetes is
  'strategic', which does not work with Custom Resources.
* This also updates the resource example to demonstrate how it is used

api/openapi-spec/swagger.json

@@ -538,6 +538,10 @@
           "description": "Manifest contains the kubernetes manifest",
           "type": "string"
         },
+        "mergeStrategy": {
+          "description": "MergeStrategy is the strategy used to merge a patch. It defaults to \"strategic\" Must be one of: strategic, merge, json",
+          "type": "string"
+        },
         "successCondition": {
           "description": "SuccessCondition is a label selector expression which describes the conditions of the k8s resource in which it is acceptable to proceed to the following step",
           "type": "string"

examples/README.md

@@ -1164,7 +1164,6 @@ spec:
   - name: pi-tmpl
     resource:                   # indicates that this is a resource template
       action: create            # can be any kubectl action (e.g. create, delete, apply, patch) 
-                                # Patch action will support only **json merge strategic**
       # The successCondition and failureCondition are optional expressions.
       # If failureCondition is true, the step is considered failed.
       # If successCondition is true, the step is considered successful.
@@ -1194,6 +1193,39 @@ spec:
 
 Resources created in this way are independent of the workflow. If you want the resource to be deleted when the workflow is deleted then you can use [Kubernetes garbage collection](https://kubernetes.io/docs/concepts/workloads/controllers/garbage-collection/) with the workflow resource as an owner reference ([example](./k8s-owner-reference.yaml)).
 
+**Note:**
+When patching, the resource will accept another attribute, `mergeStrategy`, which can either be `strategic`, `merge`, or `json`. If this attribute is not supplied, it will default to `strategic`. Keep in mind that Custom Resources cannot be patched with `strategic`, so a different strategy must be chosen. For example, suppose you have the [CronTab CustomResourceDefinition](https://kubernetes.io/docs/tasks/access-kubernetes-api/custom-resources/custom-resource-definitions/#create-a-customresourcedefinition) defined, and the following instance of a CronTab:
+
+```yaml
+apiVersion: "stable.example.com/v1"
+kind: CronTab
+spec:
+  cronSpec: "* * * * */5"
+  image: my-awesome-cron-image
+```
+
+This Crontab can be modified using the following Argo Workflow:
+
+```yaml
+apiVersion: argoproj.io/v1alpha1
+kind: Workflow
+metadata:
+  generateName: k8s-patch-
+spec:
+  entrypoint: cront-tmpl
+  templates:
+  - name: cront-tmpl
+    resource:
+      action: patch
+      mergeStrategy: merge                 # Must be one of [strategic merge json]
+      manifest: |
+        apiVersion: "stable.example.com/v1"
+        kind: CronTab
+        spec:
+          cronSpec: "* * * * */10"
+          image: my-awesome-cron-image
+```
+
 ## Docker-in-Docker Using Sidecars
 
 An application of sidecars is to implement Docker-in-Docker (DinD). DinD is useful when you want to run Docker commands from inside a container. For example, you may want to build and push a container image from inside your build container. In the following example, we use the docker:dind container to run a Docker daemon in a sidecar and give the main container access to the daemon.

pkg/apis/workflow/v1alpha1/types.go

@@ -781,6 +781,10 @@ type ResourceTemplate struct {
 	// Must be one of: get, create, apply, delete, replace
 	Action string `json:"action"`
 
+	// MergeStrategy is the strategy used to merge a patch. It defaults to "strategic"
+	// Must be one of: strategic, merge, json
+	MergeStrategy string `json:"mergeStrategy,omitempty"`
+
 	// Manifest contains the kubernetes manifest
 	Manifest string `json:"manifest"`
 

workflow/executor/resource.go

@@ -31,6 +31,13 @@ func (we *WorkflowExecutor) ExecResource(action string, manifestPath string, isD
 	}
 
 	if action == "patch" {
+		mergeStrategy := "strategic"
+		if we.Template.Resource.MergeStrategy != "" {
+			mergeStrategy = we.Template.Resource.MergeStrategy
+		}
+
+		args = append(args, "--type")
+		args = append(args, mergeStrategy)
 
 		args = append(args, "-p")
 		buff, err := ioutil.ReadFile(manifestPath)