fix: allow caching run layers with no filesystem changes

Fixes #326

Author: mafredri

envbuilder.go

@@ -456,17 +456,18 @@ func Run(ctx context.Context, opts options.Options) error {
 			}
 			kOpts := &config.KanikoOptions{
 				// Boilerplate!
-				CustomPlatform:    platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
-				SnapshotMode:      "redo",
-				RunV2:             true,
-				RunStdout:         stdoutWriter,
-				RunStderr:         stderrWriter,
-				Destinations:      destinations,
-				NoPush:            !opts.PushImage || len(destinations) == 0,
-				CacheRunLayers:    true,
-				CacheCopyLayers:   true,
-				CompressedCaching: true,
-				Compression:       config.ZStd,
+				CustomPlatform:     platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
+				SnapshotMode:       "redo",
+				RunV2:              true,
+				RunStdout:          stdoutWriter,
+				RunStderr:          stderrWriter,
+				Destinations:       destinations,
+				NoPush:             !opts.PushImage || len(destinations) == 0,
+				CacheRunLayers:     true,
+				CacheCopyLayers:    true,
+				ForceBuildMetadata: opts.PushImage, // Force layers with no changes to be cached, required for cache probing.
+				CompressedCaching:  true,
+				Compression:        config.ZStd,
 				// Maps to "default" level, ~100-300 MB/sec according to
 				// benchmarks in klauspost/compress README
 				// https://github.com/klauspost/compress/blob/67a538e2b4df11f8ec7139388838a13bce84b5d5/zstd/encoder_options.go#L188
@@ -1180,17 +1181,18 @@ func RunCacheProbe(ctx context.Context, opts options.Options) (v1.Image, error)
 	}
 	kOpts := &config.KanikoOptions{
 		// Boilerplate!
-		CustomPlatform:    platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
-		SnapshotMode:      "redo",
-		RunV2:             true,
-		RunStdout:         stdoutWriter,
-		RunStderr:         stderrWriter,
-		Destinations:      destinations,
-		NoPush:            !opts.PushImage || len(destinations) == 0,
-		CacheRunLayers:    true,
-		CacheCopyLayers:   true,
-		CompressedCaching: true,
-		Compression:       config.ZStd,
+		CustomPlatform:     platforms.Format(platforms.Normalize(platforms.DefaultSpec())),
+		SnapshotMode:       "redo",
+		RunV2:              true,
+		RunStdout:          stdoutWriter,
+		RunStderr:          stderrWriter,
+		Destinations:       destinations,
+		NoPush:             true,
+		CacheRunLayers:     true,
+		CacheCopyLayers:    true,
+		ForceBuildMetadata: true, // Force layers with no changes to be cached, required for cache probing.
+		CompressedCaching:  true,
+		Compression:        config.ZStd,
 		// Maps to "default" level, ~100-300 MB/sec according to
 		// benchmarks in klauspost/compress README
 		// https://github.com/klauspost/compress/blob/67a538e2b4df11f8ec7139388838a13bce84b5d5/zstd/encoder_options.go#L188

integration/integration_test.go

@@ -1312,6 +1312,56 @@ RUN date --utc > /root/date.txt`, testImageAlpine),
 		require.NotEmpty(t, strings.TrimSpace(out))
 	})
 
+	t.Run("CacheAndPushWithNoChangeLayers", func(t *testing.T) {
+		t.Parallel()
+
+		ctx, cancel := context.WithCancel(context.Background())
+		t.Cleanup(cancel)
+
+		srv := gittest.CreateGitServer(t, gittest.Options{
+			Files: map[string]string{
+				"Dockerfile": fmt.Sprintf(`
+FROM %[1]s
+RUN touch /foo
+RUN echo "Hi, please don't put me in a layer (I guess you won't listen to me...)"
+RUN touch /bar
+`, testImageAlpine),
+			},
+		})
+
+		// Given: an empty registry
+		testReg := setupInMemoryRegistry(t, setupInMemoryRegistryOpts{})
+		testRepo := testReg + "/test"
+		ref, err := name.ParseReference(testRepo + ":latest")
+		require.NoError(t, err)
+		_, err = remote.Image(ref)
+		require.ErrorContains(t, err, "NAME_UNKNOWN", "expected image to not be present before build + push")
+
+		opts := []string{
+			envbuilderEnv("GIT_URL", srv.URL),
+			envbuilderEnv("CACHE_REPO", testRepo),
+			envbuilderEnv("DOCKERFILE_PATH", "Dockerfile"),
+		}
+
+		// When: we run envbuilder with PUSH_IMAGE set
+		_ = pushImage(t, ref, nil, opts...)
+
+		cli, err := client.NewClientWithOpts(client.FromEnv, client.WithAPIVersionNegotiation())
+		require.NoError(t, err)
+		defer cli.Close()
+
+		// Then: re-running envbuilder with GET_CACHED_IMAGE should succeed
+		cachedRef := getCachedImage(ctx, t, cli, opts...)
+
+		// When: we run the image we just built
+		ctr := startContainerFromRef(ctx, t, cli, cachedRef)
+
+		// Then: the envbuilder binary exists in the image!
+		out := execContainer(t, ctr.ID, "/.envbuilder/bin/envbuilder --help")
+		require.Regexp(t, `(?s)^USAGE:\s+envbuilder`, strings.TrimSpace(out))
+		require.NotEmpty(t, strings.TrimSpace(out))
+	})
+
 	t.Run("CacheAndPushAuth", func(t *testing.T) {
 		t.Parallel()