build: Add ability to override images with YAML

cmd/moby/build.go

@@ -201,6 +201,7 @@ func build(args []string) {
 		}
 		m = moby.AppendConfig(m, c)
 	}
+	m = moby.ApplyOverride(m)
 
 	if *buildDisableTrust {
 		log.Debugf("Disabling content trust checks for this build")

src/moby/config.go

@@ -36,6 +36,10 @@ type Moby struct {
 		Optional  bool
 		Mode      string
 	}
+	Overrides []struct {
+		Source     string
+		Substitute string
+	}
 }
 
 // TrustConfig is the type of a content trust config
@@ -149,6 +153,7 @@ func AppendConfig(m0, m1 Moby) Moby {
 	moby.Files = append(moby.Files, m1.Files...)
 	moby.Trust.Image = append(moby.Trust.Image, m1.Trust.Image...)
 	moby.Trust.Org = append(moby.Trust.Org, m1.Trust.Org...)
+	moby.Overrides = append(moby.Overrides, m1.Overrides...)
 
 	return moby
 }
@@ -776,3 +781,34 @@ func ConfigInspectToOCI(yaml Image, inspect types.ImageInspect) (specs.Spec, err
 
 	return oci, nil
 }
+
+// ApplyOverride applies an override to a given config
+func ApplyOverride(config Moby) Moby {
+	for _, o := range config.Overrides {
+		if strings.Contains(config.Kernel.Image, o.Source) {
+			log.Debugf("Replacing kernel image with %s", o.Substitute)
+			config.Kernel.Image = o.Substitute
+		}
+
+		for i, img := range config.Init {
+			if strings.Contains(img, o.Source) {
+				log.Debugf("Replacing init image with %s", o.Substitute)
+				config.Init[i] = o.Substitute
+			}
+		}
+		for i, img := range config.Onboot {
+			if strings.Contains(img.Image, o.Source) {
+				log.Debugf("Replacing onboot image with %s", o.Substitute)
+				config.Onboot[i].Image = o.Substitute
+			}
+		}
+
+		for i, img := range config.Services {
+			if strings.Contains(img.Image, o.Source) {
+				log.Debugf("Replacing services image with %s", o.Substitute)
+				config.Services[i].Image = o.Substitute
+			}
+		}
+	}
+	return config
+}

src/moby/config_test.go

@@ -73,3 +73,33 @@ func TestInvalidCap(t *testing.T) {
 		t.Error("expected error, got valid OCI config")
 	}
 }
+
+func TestApplyOverride(t *testing.T) {
+	config, err := NewConfig([]byte(`
+kernel:
+  image: "foo/bar:foo"
+init:
+- foo/bar:foo
+onboot:
+  - name: foo
+    image: foo/bar:foo
+overrides:
+  - source: foo/bar
+    substitute: foo/bar:quux
+`))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	c := ApplyOverride(config)
+
+	if c.Kernel.Image != "foo/bar:quux" {
+		t.Fatalf("No override!")
+	}
+	if c.Init[0] != "foo/bar:quux" {
+		t.Fatalf("No override1!")
+	}
+	if c.Onboot[0].Image != "foo/bar:quux" {
+		t.Fatalf("No override2!")
+	}
+}

src/moby/schema.go

@@ -100,6 +100,17 @@ var schema = string(`
     "images": {
         "type": "array",
         "items": { "$ref": "#/definitions/image" }
+    },
+    "override" : {
+        "type": "object",
+        "properties": {
+            "destination": { "type": "string" },
+            "source": { "type": "string" }
+        }
+    },
+    "overrides": {
+        "type": "array",
+	"items": { "$ref": "#/definitions/override" }
     }
   },
   "properties": {
@@ -108,7 +119,8 @@ var schema = string(`
     "onboot": { "$ref": "#/definitions/images" },
     "services": { "$ref": "#/definitions/images" },
     "trust": { "$ref": "#/definitions/trust" },
-    "files": { "$ref": "#/definitions/files" }
+    "files": { "$ref": "#/definitions/files" },
+    "overrides": { "$ref": "#/definitions/overrides" }
   }
 }
 `)