Improve docker without buildpacks documentation

Explain how CDS can be enabled with plain Dockerfiles.

Closes gh-42106

spring-boot-project/spring-boot-docs/src/docs/antora/modules/how-to/pages/class-data-sharing.adoc

@@ -15,6 +15,12 @@ This will cause the buildpack to do a training run of the application, save the
 
 The Paketo Buildpack for Spring Boot https://github.com/paketo-buildpacks/spring-boot?tab=readme-ov-file#configuration[documentation] has information on other configuration options that can be enabled with builder environment variables, like `CDS_TRAINING_JAVA_TOOL_OPTIONS` that allows to override the default `JAVA_TOOL_OPTIONS`, only for the CDS training run.
 
+[[howto.class-data-sharing.dockerfiles]]
+== Packaging an Application Using CDS and Dockerfiles
+
+If you don't want to use Cloud Native Buildpacks, it is also possible to use CDS with a `Dockerfile`.
+For more information about that, please see the xref:reference:packaging/container-images/dockerfiles.adoc#packaging.container-images.dockerfiles.cds[Dockerfiles reference documentation].
+
 [[howto.class-data-sharing.training-run-configuration]]
 == Preventing Remote Services Interaction During the Training Run
 

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/pages/packaging/container-images/dockerfiles.adoc

@@ -1,7 +1,7 @@
 [[packaging.container-images.dockerfiles]]
 = Dockerfiles
 
-While it is possible to convert a Spring Boot uber jar into a Docker image with just a few lines in the Dockerfile, using the xref:packaging/container-images/efficient-images.adoc#packaging.container-images.efficient-images.layering[layering feature] will result in an optimized image.
+While it is possible to convert a Spring Boot uber jar into a Docker image with just a few lines in the `Dockerfile`, using the xref:packaging/container-images/efficient-images.adoc#packaging.container-images.efficient-images.layering[layering feature] will result in an optimized image.
 When you create a jar containing the layers index file, the `spring-boot-jarmode-tools` jar will be added as a dependency to your jar.
 With this jar on the classpath, you can launch your application in a special mode which allows the bootstrap code to run something entirely different from your application, for example, something that extracts the layers.
 
@@ -28,32 +28,12 @@ Available commands:
   help         Help about any command
 ----
 
-The `extract` command can be used to easily split the application into layers to be added to the Dockerfile.
-Here is an example of a Dockerfile using `jarmode`.
+The `extract` command can be used to easily split the application into layers to be added to the `Dockerfile`.
+Here is an example of a `Dockerfile` using `jarmode`.
 
 [source,dockerfile]
 ----
-# Perform the extraction in a separate builder container
-FROM bellsoft/liberica-openjre-debian:17-cds AS builder
-WORKDIR /builder
-# This points to the built jar file in the target folder
-# Adjust this to 'build/libs/*.jar' if you're using Gradle
-ARG JAR_FILE=target/*.jar
-# Copy the jar file to the working directory and rename it to application.jar
-COPY ${JAR_FILE} application.jar
-# Extract the jar file using an efficient layout
-RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted
-
-# This is the runtime container
-FROM bellsoft/liberica-openjre-debian:17-cds
-WORKDIR /application
-# Copy the extracted jar contents from the builder container into the working directory in the runtime container
-# Every copy step creates a new docker layer
-# This allows docker to only pull the changes it really needs
-COPY --from=builder /builder/extracted/dependencies/ ./
-COPY --from=builder /builder/extracted/spring-boot-loader/ ./
-COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
-COPY --from=builder /builder/extracted/application/ ./
+include::reference:partial$dockerfile[]
 # Start the application jar - this is not the uber jar used by the builder
 # This jar only contains application code and references to the extracted jar files
 # This layout is efficient to start up and CDS friendly
@@ -67,10 +47,31 @@ Assuming the above `Dockerfile` is in the current directory, your Docker image c
 $ docker build --build-arg JAR_FILE=path/to/myapp.jar .
 ----
 
-This is a multi-stage Dockerfile.
+This is a multi-stage `Dockerfile`.
 The builder stage extracts the directories that are needed later.
 Each of the `COPY` commands relates to the layers extracted by the jarmode.
 
-Of course, a Dockerfile can be written without using the `jarmode`.
+Of course, a `Dockerfile` can be written without using the `jarmode`.
 You can use some combination of `unzip` and `mv` to move things to the right layer but `jarmode` simplifies that.
 Additionally, the layout created by the `jarmode` is CDS friendly out of the box.
+
+
+
+[[packaging.container-images.dockerfiles.cds]]
+== CDS
+
+If you want to additionally enable xref:reference:packaging/class-data-sharing.adoc[CDS], you can use this `Dockerfile`:
+[source,dockerfile]
+----
+include::reference:partial$dockerfile[]
+# Execute the CDS training run
+RUN java -XX:ArchiveClassesAtExit=application.jsa -Dspring.context.exit=onRefresh -jar application.jar
+# Start the application jar with CDS enabled - this is not the uber jar used by the builder
+# This jar only contains application code and references to the extracted jar files
+# This layout is efficient to start up and CDS friendly
+ENTRYPOINT ["java", "-XX:SharedArchiveFile=application.jsa", "-jar", "application.jar"]
+----
+
+This is mostly the same as the above `Dockerfile`.
+As the last steps, it creates the CDS archive by doing a training run and passes the CDS parameter to `java -jar`.
+

spring-boot-project/spring-boot-docs/src/docs/antora/modules/reference/partials/dockerfile

@@ -0,0 +1,21 @@
+# Perform the extraction in a separate builder container
+FROM bellsoft/liberica-openjre-debian:17-cds AS builder
+WORKDIR /builder
+# This points to the built jar file in the target folder
+# Adjust this to 'build/libs/*.jar' if you're using Gradle
+ARG JAR_FILE=target/*.jar
+# Copy the jar file to the working directory and rename it to application.jar
+COPY ${JAR_FILE} application.jar
+# Extract the jar file using an efficient layout
+RUN java -Djarmode=tools -jar application.jar extract --layers --destination extracted
+
+# This is the runtime container
+FROM bellsoft/liberica-openjre-debian:17-cds
+WORKDIR /application
+# Copy the extracted jar contents from the builder container into the working directory in the runtime container
+# Every copy step creates a new docker layer
+# This allows docker to only pull the changes it really needs
+COPY --from=builder /builder/extracted/dependencies/ ./
+COPY --from=builder /builder/extracted/spring-boot-loader/ ./
+COPY --from=builder /builder/extracted/snapshot-dependencies/ ./
+COPY --from=builder /builder/extracted/application/ ./