Handle the dynamic Kustomize overlay in memory

kustomize/data_source_kustomization_overlay.go

@@ -665,22 +665,25 @@ func refuseExistingKustomization(fSys filesys.FileSystem) error {
 func kustomizationOverlay(d *schema.ResourceData, m interface{}) error {
 	k := getKustomization(d)
 
-	fSys := filesys.MakeFsOnDisk()
-
 	var b bytes.Buffer
 	ye := yaml.NewEncoder(io.Writer(&b))
 	ye.Encode(k)
 	ye.Close()
 	data, _ := ioutil.ReadAll(io.Reader(&b))
 
+	fSys := makeOverlayFS(
+		filesys.MakeFsInMemory(),
+		filesys.MakeFsOnDisk(),
+	)
+
 	// error if the current working directory is already a Kustomization
 	err := refuseExistingKustomization(fSys)
 	if err != nil {
 		return err
 	}
 
-	fSys.WriteFile("Kustomization", data)
-	defer fSys.RemoveAll("Kustomization")
+	fSys.WriteFile(KFILENAME, data)
+	defer fSys.RemoveAll(KFILENAME)
 
 	rm, err := runKustomizeBuild(fSys, ".")
 	if err != nil {

kustomize/data_source_kustomization_overlay_fs.go

@@ -0,0 +1,120 @@
+package kustomize
+
+import (
+	"fmt"
+	"path/filepath"
+	"strings"
+
+	"sigs.k8s.io/kustomize/api/filesys"
+)
+
+var KFILENAME string = "Kustomization"
+
+var _ filesys.FileSystem = overlayFileSystem{}
+
+type overlayFileSystem struct {
+	upper filesys.FileSystem
+	lower filesys.FileSystem
+}
+
+// When two kustmization_overlay data sources are defined in the same root module the shared
+// file system prevents parallel execution.
+// This filesys.FileSystem implementation solves this by handling the dynamic Kustomization in memory.
+func makeOverlayFS(upper filesys.FileSystem, lower filesys.FileSystem) filesys.FileSystem {
+	return overlayFileSystem{
+		upper: upper,
+		lower: lower,
+	}
+}
+
+func (ofs overlayFileSystem) Create(name string) (filesys.File, error) {
+	return ofs.upper.Create(name)
+}
+
+func (ofs overlayFileSystem) Mkdir(name string) error {
+	return ofs.upper.Mkdir(name)
+}
+
+func (ofs overlayFileSystem) MkdirAll(name string) error {
+	return ofs.upper.MkdirAll(name)
+}
+
+func (ofs overlayFileSystem) RemoveAll(name string) error {
+	return ofs.upper.RemoveAll(name)
+}
+
+func (ofs overlayFileSystem) Open(name string) (filesys.File, error) {
+	of, err := ofs.lower.Open(name)
+
+	if err != nil {
+		return ofs.upper.Open(name)
+	}
+
+	return of, err
+}
+
+func (ofs overlayFileSystem) CleanedAbs(path string) (filesys.ConfirmedDir, string, error) {
+	cd, n, err := ofs.lower.CleanedAbs(path)
+
+	if err != nil && strings.HasSuffix(path, KFILENAME) {
+		cd, _, err = ofs.lower.CleanedAbs(".")
+		return cd, KFILENAME, err
+	}
+
+	return cd, n, err
+}
+
+func (ofs overlayFileSystem) Exists(name string) bool {
+	onDisk := ofs.lower.Exists(name)
+
+	if onDisk == false {
+		return ofs.upper.Exists(name)
+	}
+
+	return onDisk
+}
+
+func (ofs overlayFileSystem) Glob(pattern string) ([]string, error) {
+	lfs, err := ofs.lower.Glob(pattern)
+	if err != nil {
+		return lfs, err
+	}
+
+	// Glob only errors if the pattern is invalid
+	ufs, _ := ofs.lower.Glob(pattern)
+
+	return append(lfs, ufs...), nil
+
+}
+
+func (ofs overlayFileSystem) IsDir(name string) bool {
+	exl := ofs.lower.IsDir(name)
+
+	if exl == false {
+		return ofs.upper.IsDir(name)
+	}
+
+	return exl
+}
+
+func (ofs overlayFileSystem) ReadFile(name string) ([]byte, error) {
+	d, err := ofs.lower.ReadFile(name)
+
+	if err != nil && strings.HasSuffix(name, KFILENAME) {
+		return ofs.upper.ReadFile(KFILENAME)
+	}
+
+	return d, err
+}
+
+func (ofs overlayFileSystem) WriteFile(name string, c []byte) error {
+	if ofs.lower.Exists(name) {
+		return fmt.Errorf("OverlayFS: %q already exists in lower FS.", name)
+	}
+
+	return ofs.upper.WriteFile(name, c)
+}
+
+func (ofs overlayFileSystem) Walk(path string, walkFn filepath.WalkFunc) error {
+	return ofs.lower.Walk(path, walkFn)
+}