Configure Docker host in build plugins

This commit adds the ability to configure the Maven and Gradle
plugins to use a remote Docker daemon using build file
configuration, as an alternative to setting environment variables
to specify remote host connection details.

Fixes gh-23400

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/asciidoc/packaging-oci-image.adoc

@@ -34,6 +34,24 @@ The following table shows the environment variables and their values:
 
 On Linux and macOS, these environment variables can be set using the command `eval $(minikube docker-env)` after minikube has been started.
 
+Docker daemon connection information can also be provided using `docker` properties in the plugin configuration.
+The following table summarizes the available properties:
+
+|===
+| Property | Description
+
+| `host`
+| URL containing the host and port for the Docker daemon - e.g. `tcp://192.168.99.100:2376`
+
+| `tlsVerify`
+| Enable secure HTTPS protocol when set to `true` (optional)
+
+| `certPath`
+| Path to certificate and key files for HTTPS (required if `tlsVerify` is `true`, ignored otherwise)
+|===
+
+For more details, see also <<build-image-example-docker,examples>>.
+
 
 
 [[build-image-docker-registry]]
@@ -220,7 +238,21 @@ The image name can be specified on the command line as well, as shown in this ex
 
 [[build-image-example-docker]]
 ==== Docker Configuration
-If the builder or run image are stored in a private Docker registry that supports user authentication, authentication details can be provided as shown in the following example:
+If you need the plugin to communicate with the Docker daemon using a remote connection instead of the default local connection, the connection details can be provided using `docker` properties as shown in the following example:
+
+[source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
+.Groovy
+----
+include::../gradle/packaging/boot-build-image-docker-host.gradle[tags=docker-host]
+----
+
+[source,kotlin,indent=0,subs="verbatim,attributes",role="secondary"]
+.Kotlin
+----
+include::../gradle/packaging/boot-build-image-docker-host.gradle.kts[tags=docker-host]
+----
+
+If the builder or run image are stored in a private Docker registry that supports user authentication, authentication details can be provided using `docker.registry` properties as shown in the following example:
 
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy
@@ -234,7 +266,7 @@ include::../gradle/packaging/boot-build-image-docker-auth-user.gradle[tags=docke
 include::../gradle/packaging/boot-build-image-docker-auth-user.gradle.kts[tags=docker-auth-user]
 ----
 
-If the builder or run image is stored in a private Docker registry that supports token authentication, the token value can be provided as shown in the following example:
+If the builder or run image is stored in a private Docker registry that supports token authentication, the token value can be provided using `docker.registry` as shown in the following example:
 
 [source,groovy,indent=0,subs="verbatim,attributes",role="primary"]
 .Groovy

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/gradle/packaging/boot-build-image-docker-host.gradle

@@ -0,0 +1,18 @@
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{gradle-project-version}'
+}
+
+bootJar {
+	mainClassName 'com.example.ExampleApplication'
+}
+
+// tag::docker-host[]
+bootBuildImage {
+	docker {
+		host = "tcp://192.168.99.100:2376"
+		tlsVerify = true
+		certPath = "/home/users/.minikube/certs"
+	}
+}
+// end::docker-host[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/docs/gradle/packaging/boot-build-image-docker-host.gradle.kts

@@ -0,0 +1,21 @@
+import org.springframework.boot.gradle.tasks.bundling.BootJar
+import org.springframework.boot.gradle.tasks.bundling.BootBuildImage
+
+plugins {
+	java
+	id("org.springframework.boot") version "{gradle-project-version}"
+}
+
+tasks.getByName<BootJar>("bootJar") {
+	mainClassName = "com.example.ExampleApplication"
+}
+
+// tag::docker-host[]
+tasks.getByName<BootBuildImage>("bootBuildImage") {
+	docker {
+		host = "tcp://192.168.99.100:2376"
+		tlsVerify = true
+		certPath = "/home/users/.minikube/certs"
+	}
+}
+// end::docker-host[]

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/bundling/DockerSpec.java

@@ -35,6 +35,12 @@ import org.springframework.boot.buildpack.platform.docker.configuration.DockerCo
  */
 public class DockerSpec {
 
+	private String host;
+
+	private boolean tlsVerify;
+
+	private String certPath;
+
 	private final DockerRegistrySpec registry;
 
 	public DockerSpec() {
@@ -45,6 +51,36 @@ public class DockerSpec {
 		this.registry = registry;
 	}
 
+	@Input
+	@Optional
+	public String getHost() {
+		return this.host;
+	}
+
+	public void setHost(String host) {
+		this.host = host;
+	}
+
+	@Input
+	@Optional
+	public Boolean isTlsVerify() {
+		return this.tlsVerify;
+	}
+
+	public void setTlsVerify(boolean tlsVerify) {
+		this.tlsVerify = tlsVerify;
+	}
+
+	@Input
+	@Optional
+	public String getCertPath() {
+		return this.certPath;
+	}
+
+	public void setCertPath(String certPath) {
+		this.certPath = certPath;
+	}
+
 	/**
 	 * Returns the {@link DockerRegistrySpec} that configures registry authentication.
 	 * @return the registry spec
@@ -77,14 +113,28 @@ public class DockerSpec {
 	 * @return the Docker configuration
 	 */
 	DockerConfiguration asDockerConfiguration() {
+		DockerConfiguration dockerConfiguration = new DockerConfiguration();
+		dockerConfiguration = customizeHost(dockerConfiguration);
+		dockerConfiguration = customizeAuthentication(dockerConfiguration);
+		return dockerConfiguration;
+	}
+
+	private DockerConfiguration customizeHost(DockerConfiguration dockerConfiguration) {
+		if (this.host != null) {
+			return dockerConfiguration.withHost(this.host, this.tlsVerify, this.certPath);
+		}
+		return dockerConfiguration;
+	}
+
+	private DockerConfiguration customizeAuthentication(DockerConfiguration dockerConfiguration) {
 		if (this.registry == null || this.registry.hasEmptyAuth()) {
-			return null;
+			return dockerConfiguration;
 		}
 		if (this.registry.hasTokenAuth() && !this.registry.hasUserAuth()) {
-			return DockerConfiguration.withRegistryTokenAuthentication(this.registry.getToken());
+			return dockerConfiguration.withRegistryTokenAuthentication(this.registry.getToken());
 		}
 		if (this.registry.hasUserAuth() && !this.registry.hasTokenAuth()) {
-			return DockerConfiguration.withRegistryUserAuthentication(this.registry.getUsername(),
+			return dockerConfiguration.withRegistryUserAuthentication(this.registry.getUsername(),
 					this.registry.getPassword(), this.registry.getUrl(), this.registry.getEmail());
 		}
 		throw new GradleException(

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/DockerSpecTests.java

@@ -20,6 +20,7 @@ import org.gradle.api.GradleException;
 import org.junit.jupiter.api.Test;
 
 import org.springframework.boot.buildpack.platform.docker.configuration.DockerConfiguration;
+import org.springframework.boot.buildpack.platform.docker.configuration.DockerHost;
 import org.springframework.boot.buildpack.platform.docker.configuration.DockerRegistryAuthentication;
 import org.springframework.util.Base64Utils;
 
@@ -35,15 +36,36 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 public class DockerSpecTests {
 
 	@Test
-	void asDockerConfigurationWithoutRegistry() {
+	void asDockerConfigurationWithDefaults() {
 		DockerSpec dockerSpec = new DockerSpec();
-		assertThat(dockerSpec.asDockerConfiguration()).isNull();
+		assertThat(dockerSpec.asDockerConfiguration().getHost()).isNull();
+		assertThat(dockerSpec.asDockerConfiguration().getRegistryAuthentication()).isNull();
 	}
 
 	@Test
-	void asDockerConfigurationWithEmptyRegistry() {
-		DockerSpec dockerSpec = new DockerSpec(new DockerSpec.DockerRegistrySpec());
-		assertThat(dockerSpec.asDockerConfiguration()).isNull();
+	void asDockerConfigurationWithHostConfiguration() {
+		DockerSpec dockerSpec = new DockerSpec();
+		dockerSpec.setHost("docker.example.com");
+		dockerSpec.setTlsVerify(true);
+		dockerSpec.setCertPath("/tmp/ca-cert");
+		DockerConfiguration dockerConfiguration = dockerSpec.asDockerConfiguration();
+		DockerHost host = dockerConfiguration.getHost();
+		assertThat(host.getAddress()).isEqualTo("docker.example.com");
+		assertThat(host.isSecure()).isEqualTo(true);
+		assertThat(host.getCertificatePath()).isEqualTo("/tmp/ca-cert");
+		assertThat(dockerSpec.asDockerConfiguration().getRegistryAuthentication()).isNull();
+	}
+
+	@Test
+	void asDockerConfigurationWithHostConfigurationNoTlsVerify() {
+		DockerSpec dockerSpec = new DockerSpec();
+		dockerSpec.setHost("docker.example.com");
+		DockerConfiguration dockerConfiguration = dockerSpec.asDockerConfiguration();
+		DockerHost host = dockerConfiguration.getHost();
+		assertThat(host.getAddress()).isEqualTo("docker.example.com");
+		assertThat(host.isSecure()).isEqualTo(false);
+		assertThat(host.getCertificatePath()).isNull();
+		assertThat(dockerSpec.asDockerConfiguration().getRegistryAuthentication()).isNull();
 	}
 
 	@Test
@@ -61,6 +83,7 @@ public class DockerSpecTests {
 				.contains("\"username\" : \"user\"").contains("\"password\" : \"secret\"")
 				.contains("\"email\" : \"docker@example.com\"")
 				.contains("\"serveraddress\" : \"https://docker.example.com\"");
+		assertThat(dockerSpec.asDockerConfiguration().getHost()).isNull();
 	}
 
 	@Test