Don't provision volumeMount for empty artifacts

workflow/controller/workflowpod.go

@@ -702,6 +702,11 @@ func (woc *wfOperationCtx) addInputArtifactsVolumes(pod *apiv1.Pod, tmpl *wfv1.T
 		if art.Path == "" {
 			return errors.Errorf(errors.CodeBadRequest, "inputs.artifacts.%s did not specify a path", art.Name)
 		}
+		if !art.HasLocation() && art.Optional {
+			woc.log.Infof("skip volume mount of %s (%s): optional artifact was not provided",
+				art.Name, art.Path)
+			continue
+		}
 		overlap := common.FindOverlappingVolume(tmpl, art.Path)
 		if overlap != nil {
 			// artifact path overlaps with a mounted volume. do not mount the

workflow/controller/workflowpod_test.go

@@ -77,6 +77,65 @@ func TestScriptTemplateWithVolume(t *testing.T) {
 	assert.NoError(t, err)
 }
 
+var scriptTemplateWithOptionalInputArtifactProvided = `
+name: script-with-input-artifact
+inputs:
+  artifacts:
+  - name: manifest
+    path: /manifest
+    optional: true
+    http:
+        url: https://raw.githubusercontent.com/argoproj/argo/stable/manifests/install.yaml
+script:
+  image: alpine:latest
+  command: [sh]
+  source: |
+    ls -al
+`
+
+var scriptTemplateWithOptionalInputArtifactNotProvided = `
+name: script-with-input-artifact
+inputs:
+  artifacts:
+  - name: manifest
+    path: /manifest
+    optional: true
+script:
+  image: alpine:latest
+  command: [sh]
+  source: |
+    ls -al
+`
+// TestScriptTemplateWithVolume ensure we can a script pod with input artifacts
+func TestScriptTemplateWithoutVolumeOptionalArtifact(t *testing.T) {
+	volumeMount := apiv1.VolumeMount{
+		Name: "input-artifacts",
+		ReadOnly: false,
+		MountPath: "/manifest",
+		SubPath: "manifest",
+		MountPropagation: nil,
+		SubPathExpr: "",
+	}
+
+	// Ensure that volume mount is added when artifact is provided
+	tmpl := unmarshalTemplate(scriptTemplateWithOptionalInputArtifactProvided)
+	woc := newWoc()
+	mainCtr := tmpl.Script.Container
+	mainCtr.Args = append(mainCtr.Args, common.ExecutorScriptSourcePath)
+	pod, err := woc.createWorkflowPod(tmpl.Name, mainCtr, tmpl, true)
+	assert.NoError(t, err)
+	assert.Contains(t, pod.Spec.Containers[1].VolumeMounts, volumeMount)
+
+	// Ensure that volume mount is not created when artifact is not provided
+	tmpl = unmarshalTemplate(scriptTemplateWithOptionalInputArtifactNotProvided)
+	woc = newWoc()
+	mainCtr = tmpl.Script.Container
+	mainCtr.Args = append(mainCtr.Args, common.ExecutorScriptSourcePath)
+	pod, err = woc.createWorkflowPod(tmpl.Name, mainCtr, tmpl, true)
+	assert.NoError(t, err)
+	assert.NotContains(t, pod.Spec.Containers[1].VolumeMounts, volumeMount)
+}
+
 // TestWFLevelServiceAccount verifies the ability to carry forward the service account name
 // for the pod from workflow.spec.serviceAccountName.
 func TestWFLevelServiceAccount(t *testing.T) {