Add builderFor label to ephemeral builder image

Adding a label to the ephemeral builder image cloned from the base
builder image eliminates contention between builds that are run
concurrently. Without this label, concurrent builds could result in
a race condition in the Docker daemon if the ephemeral builder image
shared by builds was deleted by both builds at exactly the same time.

Fixes gh-27888

Author: scottfrederick

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/build/Builder.java

@@ -96,8 +96,8 @@ public void build(BuildRequest request) throws DockerEngineException, IOExceptio
 		BuilderMetadata builderMetadata = BuilderMetadata.fromImage(builderImage);
 		BuildOwner buildOwner = BuildOwner.fromEnv(builderImage.getConfig().getEnv());
 		request = determineRunImage(request, builderImage, builderMetadata.getStack());
-		EphemeralBuilder builder = new EphemeralBuilder(buildOwner, builderImage, builderMetadata, request.getCreator(),
-				request.getEnv());
+		EphemeralBuilder builder = new EphemeralBuilder(buildOwner, builderImage, request.getName(), builderMetadata,
+				request.getCreator(), request.getEnv());
 		this.docker.image().load(builder.getArchive(), UpdateListener.none());
 		try {
 			executeLifecycle(request, builder);

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/main/java/org/springframework/boot/buildpack/platform/build/EphemeralBuilder.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -34,6 +34,8 @@
  */
 class EphemeralBuilder {
 
+	static final String BUILDER_FOR_LABEL_NAME = "org.springframework.boot.builderFor";
+
 	private final BuildOwner buildOwner;
 
 	private final BuilderMetadata builderMetadata;
@@ -45,20 +47,22 @@ class EphemeralBuilder {
 	/**
 	 * Create a new {@link EphemeralBuilder} instance.
 	 * @param buildOwner the build owner
-	 * @param builderImage the image
+	 * @param builderImage the base builder image
+	 * @param targetImage the image being built
 	 * @param builderMetadata the builder metadata
 	 * @param creator the builder creator
 	 * @param env the builder env
 	 * @throws IOException on IO error
 	 */
-	EphemeralBuilder(BuildOwner buildOwner, Image builderImage, BuilderMetadata builderMetadata, Creator creator,
-			Map<String, String> env) throws IOException {
+	EphemeralBuilder(BuildOwner buildOwner, Image builderImage, ImageReference targetImage,
+			BuilderMetadata builderMetadata, Creator creator, Map<String, String> env) throws IOException {
 		ImageReference name = ImageReference.random("pack.local/builder/").inTaggedForm();
 		this.buildOwner = buildOwner;
 		this.creator = creator;
 		this.builderMetadata = builderMetadata.copy(this::updateMetadata);
 		this.archive = ImageArchive.from(builderImage, (update) -> {
 			update.withUpdatedConfig(this.builderMetadata::attachTo);
+			update.withUpdatedConfig((config) -> config.withLabel(BUILDER_FOR_LABEL_NAME, targetImage.toString()));
 			update.withTag(name);
 			if (env != null && !env.isEmpty()) {
 				update.withNewLayer(getEnvLayer(env));

spring-boot-project/spring-boot-tools/spring-boot-buildpack-platform/src/test/java/org/springframework/boot/buildpack/platform/build/EphemeralBuilderTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -42,6 +42,7 @@
 import org.springframework.boot.buildpack.platform.json.AbstractJsonTests;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.entry;
 
 /**
  * Tests for {@link EphemeralBuilder}.
@@ -58,15 +59,18 @@ class EphemeralBuilderTests extends AbstractJsonTests {
 
 	private Image image;
 
+	private ImageReference targetImage;
+
 	private BuilderMetadata metadata;
 
 	private Map<String, String> env;
 
-	private Creator creator = Creator.withVersion("dev");
+	private final Creator creator = Creator.withVersion("dev");
 
 	@BeforeEach
 	void setup() throws Exception {
 		this.image = Image.of(getContent("image.json"));
+		this.targetImage = ImageReference.of("my-image:latest");
 		this.metadata = BuilderMetadata.fromImage(this.image);
 		this.env = new HashMap<>();
 		this.env.put("spring", "boot");
@@ -75,15 +79,18 @@ void setup() throws Exception {
 
 	@Test
 	void getNameHasRandomName() throws Exception {
-		EphemeralBuilder b1 = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
-		EphemeralBuilder b2 = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
+		EphemeralBuilder b1 = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
+		EphemeralBuilder b2 = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
 		assertThat(b1.getName().toString()).startsWith("pack.local/builder/").endsWith(":latest");
 		assertThat(b1.getName().toString()).isNotEqualTo(b2.getName().toString());
 	}
 
 	@Test
 	void getArchiveHasCreatedByConfig() throws Exception {
-		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
+		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
 		ImageConfig config = builder.getArchive().getImageConfig();
 		BuilderMetadata ephemeralMetadata = BuilderMetadata.fromImageConfig(config);
 		assertThat(ephemeralMetadata.getCreatedBy().getName()).isEqualTo("Spring Boot");
@@ -92,14 +99,16 @@ void getArchiveHasCreatedByConfig() throws Exception {
 
 	@Test
 	void getArchiveHasTag() throws Exception {
-		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
+		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
 		ImageReference tag = builder.getArchive().getTag();
 		assertThat(tag.toString()).startsWith("pack.local/builder/").endsWith(":latest");
 	}
 
 	@Test
 	void getArchiveHasFixedCreateDate() throws Exception {
-		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
+		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
 		Instant createInstant = builder.getArchive().getCreateDate();
 		OffsetDateTime createDateTime = OffsetDateTime.ofInstant(createInstant, ZoneId.of("UTC"));
 		assertThat(createDateTime.getYear()).isEqualTo(1980);
@@ -112,12 +121,22 @@ void getArchiveHasFixedCreateDate() throws Exception {
 
 	@Test
 	void getArchiveContainsEnvLayer() throws Exception {
-		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.metadata, this.creator, this.env);
+		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
 		File directory = unpack(getLayer(builder.getArchive(), 0), "env");
 		assertThat(new File(directory, "platform/env/spring")).usingCharset(StandardCharsets.UTF_8).hasContent("boot");
 		assertThat(new File(directory, "platform/env/empty")).usingCharset(StandardCharsets.UTF_8).hasContent("");
 	}
 
+	@Test
+	void getArchiveHasBuilderForLabel() throws Exception {
+		EphemeralBuilder builder = new EphemeralBuilder(this.owner, this.image, this.targetImage, this.metadata,
+				this.creator, this.env);
+		ImageConfig config = builder.getArchive().getImageConfig();
+		assertThat(config.getLabels())
+				.contains(entry(EphemeralBuilder.BUILDER_FOR_LABEL_NAME, this.targetImage.toString()));
+	}
+
 	private TarArchiveInputStream getLayer(ImageArchive archive, int index) throws Exception {
 		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
 		archive.writeTo(outputStream);