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Multi-Cloud Apps with GraalVM - Up and Running

This workshop is for developers looking to understand better how to build size-optimized cloud native Java applications using GraalVM Native Image. You are going to discover ways to minimize application footprint by taking advantage of different Native Image linking options and packaging into various base containers.

For the demo part, you will run a Spring Boot web server application, hosting the GraalVM website. Spring Boot 3 has integrated support for GraalVM Native Image, making it easier to set up and configure a project. Compiling a Spring Boot application ahead of time can significantly boost the performance and reduce its footprint.

Workshop Objectives

In this workshop you will:

  • Learn how to compile a Spring Boot application ahead-of-time into a native executable and optimize it for file size.
  • See how to use the GraalVM Native Image Maven Plugin.
  • Create native executables and run them inside different Docker containers.
  • Shrink a container image size by taking advantage of different Native Image containerisation and linking options.
  • Compare the deployed container images sizes.
  • See how to use GitHub Actions to automate the build of native executables as part of a CI/CD pipeline.

Prerequisites

Setup

Clone this repository with Git and enter the application directory:

git clone https://github.com/olyagpl/spring-boot-webserver.git 
cd spring-boot-webserver

STEP 1: Compile and Run the Application from a JAR File Inside a Container

Start by compiling and running the application from a JAR file inside a Docker container. It requires a container image with a full JDK and runtime libraries.

Explanation

The Dockerfile, provided for this step, Dockerfile.distroless-base.uber-jar, uses Oracle GraalVM for JDK 23 container image for the builder, and Debian Slim Linux image for the runtime. The entrypoint for this image is equivalent to java -jar, so only a path to a JAR file is specified in CMD.

Action

  1. Run the build-jar.sh script from the application directory:

    ./build-jar.sh

  2. Once the script finishes, a container image debian-slim.jar should be available. Start the application using docker run:

    docker run --rm -p8080:8080 webserver:debian-slim.jar

    The container started in hundreds of milliseconds, 1.135 seconds.

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C. (The Docker runs in an attached mode.)

  5. Check the container size:

    docker images

    The expected size is ~240MB. Note that the website pages added 44MB to the container size.

    REPOSITORY   TAG               IMAGE ID       CREATED             SIZE
webserver    debian-slim.jar   5c69f06a3972   About an hour ago   238MB

STEP 2: Build and Run a Jlink Custom Runtime Image Inside a Container

In this step, you will create a custom runtime of this Spring Boot web server with Jlink and run it inside a container image. See how much reduction in size you can gain.

Explanation

Jlink, or jlink, is a tool that generates a custom Java runtime image that contains only the platform modules that are required for your application. This is one of the approaches to create cloud native applications introduced in Java 11.

The script build-jlink.sh that runs docker build using the Dockerfile.distroless-java-base.jlink. The Dockerfile contains a multistage build: first it generates a Jlink custom runtime on a full JDK; then copies the runtime image folder along with static website pages into a Java base container image, and sets the entrypoint.

The application does not have to be modular, but you need to figure out which modules the application depends on to be able to jlink it. In the builder stage, running on a full JDK, after compiling the project, Docker generates a file cp.txt containing the classpath with all the dependencies:

RUN ./mvnw dependency:build-classpath -Dmdep.outputFile=cp.txt

Then, Docker runs the jdeps command with the classpath to check required modules for this Spring Boot application:

RUN jdeps --ignore-missing-deps -q  --recursive --multi-release 23 --print-module-deps --class-path $(cat cp.txt) target/webserver-0.0.1-SNAPSHOT.jar

Finally, Docker runs jlink to create a custom runtime in the specified output directory jlink-jre. The ENTRYPOINT for the application would be java from the custom runtime.

Action

  1. Run the script:

    ./build-jlink.sh

  2. Once the script finishes, a container image distroless-java-base.jlink should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:distroless-java-base.jlink

    The container started in 1.224 seconds.

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C.

  5. Compare the file size of container images:

    docker images

    The expected output is:

    REPOSITORY   TAG                          IMAGE ID       CREATED          SIZE
webserver    distroless-java-base.jlink   687f7683ad58   16 minutes ago   192MB
webserver    debian-slim.jar              5c69f06a3972   2 hours ago      238MB

    Jlink shrinked the container by 46MB.

STEP 3: Build and Run a Native Image Inside a Container Using Paketo Buildpacks

In this step, you will compile this Spring Boot application ahead of time with GraalVM Native Image and run it using Paketo Buildpacks container images.

Explanation

Spring Boot supports building a native image in a container using the Paketo Buildpack for Oracle which provides GraalVM Native Image.

The mechanism is that the Paketo builder pulls the Jammy Tiny Stack image (Ubuntu distroless-like image) which contains no buildpacks. Then you point the builder image to the creator image. For this workshop, you point to the Paketo Buildpack for Oracle explicitly requesting the Native Image tool.

If you open the pom.xml file, you see the spring-boot-maven-plugin declaration added for you:

<configuration>
    <image>
    <builder>paketobuildpacks/builder-jammy-buildpackless-tiny</builder>
    <buildpacks>
        <buildpack>paketobuildpacks/oracle</buildpack>
        <buildpack>paketobuildpacks/java-native-image</buildpack>
    </buildpacks>
    </image>
</configuration>

When java-native-image is requested, the buildpack downloads Oracle GraalVM, which includes Native Image. The Paketo documentation provides several examples that show you how to build applications with Native Image using buildpacks.

Note that if you do not specify Oracle's buildpack, it will pull the default buildpack, which can result in reduced performance.

Action

  1. Build a native executable for this Spring application using the Paketo buildpack:

    ./mvnw -Pnative spring-boot:build-image

  2. Once the build completes, a container image 0.0.1-SNAPSHOT should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 docker.io/library/webserver:0.0.1-SNAPSHOT

    The application is running from the native image inside a container. The container started in just 0.031 seconds!

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C.

  5. Check the size of this container image:

    docker images

    The expected output is:

    REPOSITORY   TAG                          IMAGE ID       CREATED          SIZE
webserver    distroless-java-base.jlink   687f7683ad58   31 minutes ago   192MB
webserver    debian-slim.jar              5c69f06a3972   2 hours ago      238MB
webserver    0.0.1-SNAPSHOT               0660806da4a2   44 years ago     163MB

    The new container, tagged as 0.0.1-SNAPSHOT, is much smaller now 163MB.

STEP 4: Build a Native Image Locally and Run Inside a Container (Default Configuration)

In this step, you will create a native image with the default configuration on a host machine, and only run it inside a container.

Explanation

Spring Boot 3 has integrated support for GraalVM Native Image, making it easier to set up and configure your project. Native Build Tools project, maintained by the GraalVM team, provide Maven and Gradle plugins for building native images. The project configuration already contains all necessary plugins, including Native Image Maven plugin:

<plugin>
    <groupId>org.graalvm.buildtools</groupId>
    <artifactId>native-maven-plugin</artifactId>
</plugin>

You can build this web server ahead of time into a native executable, on your host machine, just like this: ./mvnw -Pnative native:compile. The command will compile the application and create a fully dynamically linked native image, webserver, in the target/ directory.

However, there is a script build-dynamic-image.sh, for your convenience, that does that and packages this native image in a distroless base container image with just enough to run the application. No Java Runtime Environment (JRE) is required!

Distroless container images contain only your application and its runtime dependencies. They do not contain package managers, shells or any other programs you would expect to find in a standard Linux distribution. Learn more in "Distroless" Container Images.

Action

  1. Run the script:

    ./build-dynamic-image.sh

  2. Once the build completes, a container image distroless-java-base.dynamic should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:distroless-java-base.dynamic

    The application is running from the native image inside a container. The container started in 0.033 seconds.

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C.

  5. Check the size of this container image:

    docker images

    The expected output is:

    REPOSITORY   TAG                            IMAGE ID       CREATED          SIZE
webserver    distroless-java-base.dynamic   5a5de47579ef   2 minutes ago    164MB
webserver    distroless-java-base.jlink     687f7683ad58   37 minutes ago   192MB
webserver    debian-slim.jar                5c69f06a3972   2 hours ago      238MB
webserver    0.0.1-SNAPSHOT                 0660806da4a2   44 years ago     163MB

    The new container image size 164MB it almost matches the size of the container built with Paketo Buildpacks. It is expected because it is the same native executable packaged into a different base container.

  6. Check what is the size of the native executable itself:

    ls -lh target/webserver

    The expected size is 125M. Note that the static resources are "baked" into this native executable and added 44M to its size.

STEP 5: Build a Size-Optimized Native Image Locally and Run Inside a Container

This is where the fun begins.

In this step, you will build a fully dynamically linked native image with the file size optimization on, on a host machine, and run it inside a container.

Explanation

GraalVM Native Image provides the option -Os which optimizes the resulting native image for file size. -Os enables -O2 optimizations except those that can increase code or executable size significantly. Learn more in the Native Image documentation.

For that, a separate Maven profile is provided to differentiate this run from the default build, and giving a different name for the output file:

<profile>
    <id>dynamic-size-optimized</id>
    <build>
        <plugins>
            <plugin>
                <groupId>org.graalvm.buildtools</groupId>
                <artifactId>native-maven-plugin</artifactId>
                <configuration>
                    <imageName>webserver.dynamic</imageName>
                    <buildArgs>
                        <buildArg>-Os</buildArg>
                    </buildArgs>
                </configuration>
            </plugin>
        </plugins>
    </build>
</profile>

The script build-dynamic-image.sh, available in this repository for your convenience, creates a native image with fully dynamically linked shared libraries, optimized for size, and then packages it in a distroless base container image with just enough to run the application. No Java Runtime Environment (JRE) is required.

The -Os optimization will be on for all the subsequent builds.

Action

  1. Run the script to build a size-optimized native executable and package it into a container:

    ./build-dynamic-image-optimized.sh

  2. Once the build completes, a container image distroless-java-base.dynamic-optimized should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:distroless-java-base.dynamic-optimized

    The application is running from the native image inside a container. The container started in 0.035 seconds.

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C.

  5. Check the size of this container image:

    docker images

    The expected output is:

    REPOSITORY   TAG                                      IMAGE ID       CREATED              SIZE
webserver    distroless-java-base.dynamic-optimized   0bed48dadd11   About a minute ago   130MB
webserver    distroless-java-base.dynamic             5a5de47579ef   16 minutes ago       164MB
webserver    distroless-java-base.jlink               687f7683ad58   51 minutes ago       192MB
webserver    debian-slim.jar                          5c69f06a3972   2 hours ago          238MB
webserver    0.0.1-SNAPSHOT                           0660806da4a2   44 years ago         163MB

    The size of distroless-java-base.dynamic-optimized container is cut down from 164MB to 130MB. This is because the native executable reduced in size.

  6. Check what is the size of the native executable now:

    ls -lh target/webserver

    The size decreased from 125M to 92M by applying the file size optimization.

    -rwxr-xr-x. 1 opc opc 125M Aug 29 10:51 target/webserver
-rw-r--r--. 1 opc opc  45M Aug 29 10:39 target/webserver-0.0.1-SNAPSHOT.jar
-rw-r--r--. 1 opc opc  25M Aug 29 10:39 target/webserver-0.0.1-SNAPSHOT.jar.original
-rwxr-xr-x. 1 opc opc  92M Aug 29 11:06 target/webserver.dynamic-optimized

STEP 6: Build a Size-Optimized Mostly Static Native Image Locally and Run Inside a Container

In this step, you will build a mostly static native image, with the file size optimization on, on a host machine, then package it into a container image that provides glibc, and run.

Explanation

A mostly static native image links all the shared libraries on which it relies (zlib, JDK-shared static libraries) except the standard C library, libc. This type of native image is useful for deployment on a distroless base container image. You can build a mostly statically linked image by passing the --static-nolibc option at build time.

A separate Maven profile exists for this step:

<profile>
    <id>mostly-static</id>
    <build>
        <plugins>
            <plugin>
                <groupId>org.graalvm.buildtools</groupId>
                <artifactId>native-maven-plugin</artifactId>
                <configuration>
                    <imageName>webserver.mostly-static</imageName>
                    <buildArgs>
                        <buildArg>--static-nolibc</buildArg>
                        <buildArg>-Os</buildArg>
                    </buildArgs>
                </configuration>
            </plugin>
        </plugins>
    </build>
</profile>

Action

  1. Run the script:

    ./build-mostly-static-image.sh

  2. Once the build completes, a container image distroless-base.mostly-static should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:distroless-base.mostly-static

    The application is running from the mostly static native image inside a container. The container started in 0.036 seconds.

  3. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  4. Return to the terminal and stop the running container by clicking CTRL+C.

  5. Check the size of this container image:

    docker images

    The expected output is:

    REPOSITORY   TAG                                      IMAGE ID       CREATED              SIZE
webserver    distroless-base.mostly-static            b49eec5bdfa6   About a minute ago   117MB
webserver    distroless-java-base.dynamic-optimized   0bed48dadd11   9 minutes ago        130MB
webserver    distroless-java-base.dynamic             5a5de47579ef   24 minutes ago       164MB
webserver    distroless-java-base.jlink               687f7683ad58   About an hour ago    192MB
webserver    debian-slim.jar                          5c69f06a3972   2 hours ago          238MB
webserver    0.0.1-SNAPSHOT                           0660806da4a2   44 years ago         163MB

    The size of the new distroless-base.mostly-static container is 117MB. The reduction in size is related to the fact that a smaller base image was pulled: gcr.io/distroless/base-debian12. Distroless images are very small, and the one used is only 48.3 MB. That's about 50% of the size of java-base-debian12(124 MB) used before, and 3 times less than java21-debian12 (192 MB) containing a full JDK.

    The size of the mostly static native image has not changed, and is 92MB.

STEP 7: Build a Size-Optimized Fully Static Native Image Locally and Run Inside a Container

In this step, you will build a fully static native image, with the file size optimization on, on a host machine, then package it into a scratch container.

Explanation

A fully static native image is a statically linked binary that you can use without any additional library dependencies. You can create a static native image by statically linking it against musl-libc, a lightweight, fast, and simple libc implementation. To build a fully static executable, pass the --static --libc=musl options at build time.

This static native image is easy to deploy on a slim or distroless container, even a scratch container. A scratch container is a Docker official image, useful for building super minimal images.

A separate Maven profile exists for this step:

<profile>
    <id>fully-static</id>
    <build>
        <plugins>
            <plugin>
                <groupId>org.graalvm.buildtools</groupId>
                <artifactId>native-maven-plugin</artifactId>
                <configuration>
                    <imageName>webserver.static</imageName>
                    <buildArgs>
                        <buildArg>--static --libc=musl</buildArg>
                        <buildArg>-Os</buildArg>
                    </buildArgs>
                </configuration>
            </plugin>
        </plugins>
    </build>
</profile>

Action

  1. This step requires the musl toolchain with zlib. Run the following script to download and configure the musl toolchain, and install zlib into the toolchain:

    ./setup-musl.sh

  2. Run the script to build a fully static native executable and package it into a scratch container:

    ./build-static-image.sh

  3. Once the build completes, a container image scratch.static should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:scratch.static

    The container started in 0.035 seconds. As a result you get a tiny container with a fully functional and deployable server application!

  4. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  5. Return to the terminal and stop the running container by clicking CTRL+C.

  6. Double-check if the native executable that was just created is indeed fully static with ldd:

    ldd target/webserver.static

    You should see "not a dynamic executable" for the response. Which means that the image does not rely on any libraries in the operating system environment and can be packaged in the tiniest container!

  7. Now check the size of this container image:

    docker images

    The expected output is:

    REPOSITORY   TAG                                      IMAGE ID       CREATED             SIZE
webserver    scratch.static                           6e8b25dacca6   7 minutes ago       96.4MB
webserver    distroless-base.mostly-static            b49eec5bdfa6   25 minutes ago      117MB
webserver    distroless-java-base.dynamic-optimized   0bed48dadd11   32 minutes ago      130MB
webserver    distroless-java-base.dynamic             5a5de47579ef   48 minutes ago      164MB
webserver    distroless-java-base.jlink               687f7683ad58   About an hour ago   192MB
webserver    debian-slim.jar                          5c69f06a3972   3 hours ago         238MB
webserver    0.0.1-SNAPSHOT                           0660806da4a2   44 years ago        163MB

    The container size shrinked to 96.4MB! A scratch container weights only 14.5MB.

STEP 8: Compress a Static Native Image with UPX and Run Inside a Container

Not convincing? What can you do next to reduce the size even more?

You can compress your fully static native image with UPX, then package into the same scratch container, and run.

Explanation

UPX - an advanced executable file compressor. It can significantly reduce the executable size, but note, that UPX loads the executable into the memory, unpackages it, and then recompresses.

  1. Download and install UPX:

    ./setup-upx.sh

  2. Run the script to compress the fully static executable, created at the previous step, and package it into a scratch container.

    ./build-static-upx-image.sh

  3. Once the build completes, a container image scratch.static-upx should be available. Run it, mapping the ports:

    docker run --rm -p8080:8080 webserver:scratch.static-upx

    The container started in 0.035 seconds.

  4. Open a browser and navigate to localhost:8080/. You see the GraalVM documentation pages served.

  5. Return to the terminal and stop the running container by clicking CTRL+C.

  6. Now check how much upx compressed the static native image:

    ls -lh target/webserver*

    The expected output is:

    -rwxr-xr-x. 1 opc opc 125M Aug 29 10:51 target/webserver
-rw-r--r--. 1 opc opc  45M Aug 29 11:30 target/webserver-0.0.1-SNAPSHOT.jar
-rwxr-xr-x. 1 opc opc  92M Aug 29 11:06 target/webserver.dynamic-optimized
-rwxr-xr-x. 1 opc opc  92M Aug 29 11:14 target/webserver.mostly-static
-rwxr-xr-x. 1 opc opc  92M Aug 29 11:32 target/webserver.static
-rwxr-xr-x. 1 opc opc  35M Aug 29 11:32 target/webserver.static-upx

    The webserver.static-upx is only 35MB! The upx compressed executable by 57MB from the "uncompressed" one.

  7. Lastly, check the size of all container images:

    docker images

    The expected output is:

    REPOSITORY   TAG                                      IMAGE ID       CREATED             SIZE
webserver    scratch.static-upx                       c87bfe44c7fb   6 seconds ago       36.2MB
webserver    scratch.static                           6e8b25dacca6   7 minutes ago       96.4MB
webserver    distroless-base.mostly-static            b49eec5bdfa6   25 minutes ago      117MB
webserver    distroless-java-base.dynamic-optimized   0bed48dadd11   32 minutes ago      130MB
webserver    distroless-java-base.dynamic             5a5de47579ef   48 minutes ago      164MB
webserver    distroless-java-base.jlink               687f7683ad58   About an hour ago   192MB
webserver    debian-slim.jar                          5c69f06a3972   3 hours ago         238MB
webserver    0.0.1-SNAPSHOT                           0660806da4a2   44 years ago        163MB

    The container size reduced dramatically to just 36.2MB. The application and container image's size were now shrinked to the minimum.

STEP 9: Clean up (Optional)

To clean up all images, run the ./clean.sh script provided for that purpose.

Conclusions

A fully functional and, at the same time, minimal, Java application was compiled into a native Linux executable and packaged into base, distroless, and scratch containers thanks to GraalVM Native Image's support for various linking options. All the versions of this Spring Boot application are functionally equivalent.

Sorted by size, it is clear that the fully static native image, compressed with upx, and then packaged on the scratch container is the smallest at just 36.2MB. Note that the website static pages added 44M to the container images size. Static resources are "baked” into native images.

Container Size of a build artefact
(JAR, Jlink runtime, native executable)		 Base image Container
debian-slim.jar webserver-0.0.1-SNAPSHOT.jar 44MB 192 MB 249MB
distroless-java-base.jlink jlink-jre custom runtime 68MB 128 MB 202MB
distroless-java-base.dynamic webserver 125MB 128 MB 164MB
0.0.1-SNAPSHOT 163MB
distroless-java-base.dynamic-optimized webserver-optimized 92MB 128 MB 130MB
distroless-base.mostly-static webserver.mostly-static 92MB 48.3 MB 117MB
scratch.static webserver.scratch.static 92MB 14.5 MB 96.4MB
scratch.static-upx webserver.scratch.static-upx 35MB 14.5 MB 36.2MB

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