Four Approaches to Reducing Java Startup Time

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Catherine Edelveis 🥑 Developer Advocate at BellSoft 😍Love Java, Spring, JavaFX 👩‍💻Tech writer cat_edelveis cat-edelveis.bsky.social

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Pasha Finkelshteyn 🥑 Developer Advocate at BellSoft ≈15 years in JVM, mostly @asm0dey.site asm0di0

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Together, we are…

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Together, we are… The BellSoft’s DevRel Gang!

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About BellSoft Member of: JCP Executive Committee OpenJDK Vulnerability Group GraalVM Advisory Board Linux Foundation Cloud Native Computing Foundation Founded in 2017 by Java and Linux experts with 15+ years of experience working at Sun/Oracle.

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About BellSoft Products: Liberica JDK Liberica Native Image Kit Alpaquita Linux Liberica is the JDK officially recommended by

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Enough about us :) We are here today to tell you a story about…

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YOU! Enough about us :) We are here today to tell you a story about…

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But first, four quick questions ;)

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Who knows one way to reduce the startup of their Java application?

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Who knows two ways to reduce the startup of their Java application?

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Who knows three ways to reduce the startup of their Java application?

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Who knows four ways to reduce the startup of their Java application?

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Once upon a time, all was well in one startup…

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Our startup is doing well! Java 21 LTS Spring Boot 3.4 Spring AI MongoDB, Redis JTE Deploying to the cloud @GetMapping(value = "/assistant", produces = TEXT_HTML_VALUE) public JteModel assistant() { return templates.assistantView("Bot Assistant - Chat"); }

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Starting point: Dockerfile FROM bellsoft/liberica-runtime-container:jdk-21-musl as builder ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw package FROM bellsoft/liberica-runtime-container:jre-21-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app COPY --from=builder /app/${project}/target/*.jar /app/app.jar ["j " " j " "/ / j "]

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Starting point: Dockerfile FROM bellsoft/liberica-runtime-container:jdk-21-musl as builder RUN cd ${project} && ./mvnw package ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ FROM bellsoft/liberica-runtime-container:jre-21-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app COPY --from=builder /app/${project}/target/*.jar /app/app.jar ["j " " j " "/ / j "]

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Starting point: Dockerfile FROM bellsoft/liberica-runtime-container:jre-21-musl COPY --from=builder /app/${project}/target/*.jar /app/app.jar / j ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw package ARG project ENV project=${project} RUN apk add curl WORKDIR /app ENTRYPOINT ["java", "-jar", "/app/app.jar"]

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Starting point: Dockerfile ENTRYPOINT ["java", "-jar", "/app/app.jar"] / j ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw package FROM bellsoft/liberica-runtime-container:jre-21-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app COPY --from=builder /app/${project}/target/*.jar /app/app.jar

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Starting point: Startup Total startup time of both services: 6.5 s docker compose logs chat-api bot-assistant | grep Started Started BotAssistantApplication in 2.108 seconds (process running for 3.181) Started ChatApiApplication in 2.83 seconds (process running for 3.469)

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We are growing! So many new users! Scale the services to meet the traffic

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We are growing! So many new users! Scale the services to meet the traffic But wait...

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We are growing! So many new users! Scale the services to meet the traffic But wait... Why the rollout is so slow?

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We are an agile team, we need a fast feedback loop!

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We are an agile team, we need a fast feedback loop! Need faster rollout for faster feedback

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We are an agile team, we need a fast feedback loop! Need faster rollout for faster feedback The longer the start, the slower the rollout

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We are an agile team, we need a fast feedback loop! Need faster rollout for faster feedback The longer the start, the slower the rollout Maybe Java is not cut out for the cloud?

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We are an agile team, we need a fast feedback loop! Need faster rollout for faster feedback The longer the start, the slower the rollout Maybe Java is not cut out for the cloud? Maybe it’s not too late to migrate to Go?

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Luckily, four brave developers work at this startup: The Defender The Sage The Explorer The Rebel

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They are very different, but have something in common: They care about their software product and can’t sit idle in the troubled time.

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And that’s where YOU take the stage!

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I want painless integration with no incompatibilities! The Defender

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AppCDS Save class metadata to the disc and read it from the archive Even better with Spring AOT (load even more classes!) Considerations: Use the same JVM Use the same classpath Bigger Docker image due to the archive Legal JVM Dopes Fo Legal JVM Dopes Fo… …

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process-aot org.springframework.boot spring-boot-maven-plugin process-aot

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FROM bellsoft/liberica-runtime-container:jdk-21.0.7_9-musl as builder RUN cd ${project} && ./mvnw package ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl as optimizer ARG project ENV project=${project} WORKDIR /app COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted

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FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl as optimizer COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted ADD ../pom.xml ./ RUN cd ${project} && ./mvnw package ARG project ENV project=${project} WORKDIR /app FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./

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FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted RUN apk add curl WORKDIR /app RUN java -Dspring.aot.enabled=true \ -XX:ArchiveClassesAtExit=./application.jsa \ -Dspring.context.exit=onRefresh -jar /app/app.jar ENTRYPOINT ["java", "-Dspring.aot.enabled=true", \ "-XX:SharedArchiveFile=application.jsa", \ "-jar", "/app/app.jar"]

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RUN java -Dspring.aot.enabled=true \ -XX:ArchiveClassesAtExit=./application.jsa \ -Dspring.context.exit=onRefresh -jar /app/app.jar j j j pp j y FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ ENTRYPOINT ["java", "-Dspring.aot.enabled=true", \ "-XX:SharedArchiveFile=application.jsa", \ "-jar", "/app/app.jar"]

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ENTRYPOINT ["java", "-Dspring.aot.enabled=true", \ "-XX:SharedArchiveFile=application.jsa", \ "-jar", "/app/app.jar"] j j j pp j y FROM bellsoft/liberica-runtime-container:jre-21.0.7_9-cds-musl RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ RUN java -Dspring.aot.enabled=true \ -XX:ArchiveClassesAtExit=./application.jsa \ -Dspring.context.exit=onRefresh -jar /app/app.jar

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We need to prepare ourselves and gather knowledge! The Sage

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Project Leyden Beyond AppCDS: AOT Cache with pre-compiled code Condensers -> optimizations Considerations: Still in the makings The more condensers applied, the bigger the cache

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Project Leyden Beyond AppCDS: AOT Cache with pre-compiled code Condensers -> optimizations Considerations: Still in the makings The more condensers applied, the bigger the cache Meanwhile, we can experiment!

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Let’s start with what is already implemented JEP 483: Ahead-of-Time Class Loading & Linking (JDK 24) Improve startup time by making the classes of an application instantly available, in a loaded and linked state, when the HotSpot Java Virtual Machine starts. Achieve this by monitoring the application during one run and storing the loaded and linked forms of all classes in a cache for use in subsequent runs. Lay a foundation for future improvements to both startup and warmup time.

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FROM bellsoft/liberica-runtime-container:jdk-24-musl AS builder RUN cd ${project} && ./mvnw package ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS optimizer ARG project ENV project=${project} WORKDIR /app COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS runner

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FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS optimizer COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted / pp ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw package ARG project ENV project=${project} WORKDIR /app FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS runner RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ f i i / / d/ li i / /

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FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS runner COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ WORKDIR /app COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted RUN apk add curl WORKDIR /app RUN java -Dspring.aot.enabled=true -XX:AOTMode=record \ -XX:AOTConfiguration=app.aotconf -Dspring.context.exit=onRefresh -jar /app/app.jar RUN java -Dspring.aot.enabled=true -XX:AOTMode=create \ -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -jar /app/app.jar ENTRYPOINT ["java", "-Dspring.aot.enabled=true", "-XX:AOTCache=app.aot", " j " "/ / j "]

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RUN java -Dspring.aot.enabled=true -XX:AOTMode=record \ -XX:AOTConfiguration=app.aotconf -Dspring.context.exit=onRefresh -jar /app/app.jar RUN java -Dspring.aot.enabled=true -XX:AOTMode=create \ -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -jar /app/app.jar COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS runner RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ ENTRYPOINT ["java", "-Dspring.aot.enabled=true", "-XX:AOTCache=app.aot", "-jar", "/app/app.jar"]

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ENTRYPOINT ["java", "-Dspring.aot.enabled=true", "-XX:AOTCache=app.aot", "-jar", "/app/app.jar"] COPY --from=builder /app/${project}/target/*.jar app.jar RUN java -Djarmode=tools -jar app.jar extract --layers --destination extracted FROM bellsoft/liberica-runtime-container:jre-24-cds-musl AS runner RUN apk add curl WORKDIR /app COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ RUN java -Dspring.aot.enabled=true -XX:AOTMode=record \ -XX:AOTConfiguration=app.aotconf -Dspring.context.exit=onRefresh -jar /app/app.jar RUN java -Dspring.aot.enabled=true -XX:AOTMode=create \ -XX:AOTConfiguration=app.aotconf -XX:AOTCache=app.aot -jar /app/app.jar

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Not enough? Let’s push it even further and use the builds of premain in Leyden! We will be happy to get your feedback on what’s broken!

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FROM bellsoft/alpaquita-linux-base:glibc AS downloader ADD https://is.gd/tZhyPF /java.tar.gz # just a placeholder RUN tar -zxvf java.tar.gz && mv /jdk-24 /java RUN apk add tar FROM bellsoft/alpaquita-linux-base:glibc AS builder ARG project WORKDIR /app COPY --from=downloader /java /java ADD ../pom.xml ./ ADD ${project} /app/${project} ENV JAVA_HOME=/java \ project=${project} RUN cd ${project} && ./mvnw package FROM bellsoft/alpaquita-linux-base:glibc AS optimizer ARG project

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FROM bellsoft/alpaquita-linux-base:glibc AS builder COPY --from=downloader /java /java ADD ../pom.xml ./ ADD ${project} /app/${project} ENV JAVA_HOME=/java \ RUN cd ${project} && ./mvnw package p / g / y /j g j p RUN apk add tar RUN tar -zxvf java.tar.gz && mv /jdk-24 /java ARG project WORKDIR /app project=${project} FROM bellsoft/alpaquita-linux-base:glibc AS optimizer ARG project WORKDIR /app f b ild / /${ j }/ * j j

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FROM bellsoft/alpaquita-linux-base:glibc AS optimizer COPY --from=builder /app/${project}/target/*.jar app.jar COPY --from=downloader /java /java RUN /java/bin/java -Djarmode=tools -jar app.jar extract --layers --destination extracted _ /j \ project=${project} RUN cd ${project} && ./mvnw package ARG project WORKDIR /app ENV project=${project} FROM bellsoft/alpaquita-linux-base:glibc AS runner RUN apk add curl WORKDIR /app f d l d /j /j

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FROM bellsoft/alpaquita-linux-base:glibc AS runner COPY --from=downloader /java /java COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ ENV project=${project} RUN /java/bin/java -Djarmode=tools -jar app.jar extract --layers --destination extracted RUN apk add curl WORKDIR /app RUN /java/bin/java -XX:CacheDataStore=./application.cds \ -Dspring.context.exit=onRefresh -jar /app/app.jar ENTRYPOINT ["/java/bin/java", "-XX:CacheDataStore=./application.cds", "-jar", "/app/app.jar"]

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RUN /java/bin/java -XX:CacheDataStore=./application.cds \ -Dspring.context.exit=onRefresh -jar /app/app.jar ENV project=${project} RUN /java/bin/java -Djarmode=tools -jar app.jar extract --layers --destination extracted FROM bellsoft/alpaquita-linux-base:glibc AS runner RUN apk add curl WORKDIR /app COPY --from=downloader /java /java COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ ENTRYPOINT ["/java/bin/java", "-XX:CacheDataStore=./application.cds", "-jar", "/app/app.jar"]

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ENTRYPOINT ["/java/bin/java", "-XX:CacheDataStore=./application.cds", "-jar", "/app/app.jar"] ENV project=${project} RUN /java/bin/java -Djarmode=tools -jar app.jar extract --layers --destination extracted FROM bellsoft/alpaquita-linux-base:glibc AS runner RUN apk add curl WORKDIR /app COPY --from=downloader /java /java COPY --from=optimizer /app/extracted/dependencies/ ./ COPY --from=optimizer /app/extracted/spring-boot-loader/ ./ COPY --from=optimizer /app/extracted/snapshot-dependencies/ ./ COPY --from=optimizer /app/extracted/application/ ./ RUN /java/bin/java -XX:CacheDataStore=./application.cds \ -Dspring.context.exit=onRefresh -jar /app/app.jar

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I found something exciting… Can’t wait to explore! The Explorer

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GraalVM Native Image Ahead-of-time compilation Standalone executable (.exe) No OpenJDK required to run

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Native Image: Any Considerations? Resource-demanding build process Several minutes to build the image Static compilation instead of dynamic one

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Native Image: Any Considerations? Resource-demanding build process Several minutes to build the image Static compilation instead of dynamic one Let the journey begin!

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First, let’s try it locally Build a fat JAR Build the image: The image was built, let’s run it! $JAVA_HOME/bin/native-image \ -jar bot-assistant/target/bot-assistant-1.0-SNAPSHOT-spring-boot.jar

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I never knew the journey can be so pleasant!

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I never knew the journey can be so pleasant! Uh-oh…

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A dragon! Exception in thread "main" java.lang.IllegalStateException: java.util.zip.ZipException: zip END header not found at org.springframework.boot.loader.ExecutableArchiveLauncher.(ExecutableArchiveLaun at org.springframework.boot.loader.JarLauncher.(JarLauncher.java:42) at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:65) Caused by: java.util.zip.ZipException: zip END header not found

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A dragon! java.util.zip.ZipException: zip END header not found Exception in thread "main" java.lang.IllegalStateException: at org.springframework.boot.loader.ExecutableArchiveLauncher.(ExecutableArchiveLaun at org.springframework.boot.loader.JarLauncher.(JarLauncher.java:42) at org.springframework.boot.loader.JarLauncher.main(JarLauncher.java:65) Caused by: java.util.zip.ZipException: zip END header not found

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Apparently, a known issue ➡️ Use mvn -Pnative native:compile to build the image. Maven plugin calls native-image java -jar under the hood but uses lots of flags that solve problems like the one above.

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If you use Spring Boot Parent POM, the Native Image profile is already configured! ➡️ Enable it by simply running mvn -Pnative native:compile

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Another dragon! Error: Classes that should be initialized at run time got initialized during image building: com.ctc.wstx.api.CommonConfig was unintentionally initialized at build time. com.ctc.wstx.stax.WstxInputFactory was unintentionally initialized at build time. com.ctc.wstx.api.ReaderConfig was unintentionally initialized at build time. com.ctc.wstx.util.DefaultXmlSymbolTable was unintentionally initialized at build time. To see how the classes got initialized, use --trace-class-initialization=com.ctc.wstx.api.CommonConfig,com.ctc.wstx.stax.WstxInputFactory,com

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Another dragon! Error: Classes that should be initialized at run time got initialized during image building: To see how the classes got initialized, use --trace-class-initialization=com.ctc.wstx.api.CommonConfig,com.ctc.wstx.stax.WstxInputFactory,com com.ctc.wstx.api.CommonConfig was unintentionally initialized at build time. com.ctc.wstx.stax.WstxInputFactory was unintentionally initialized at build time. com.ctc.wstx.api.ReaderConfig was unintentionally initialized at build time. com.ctc.wstx.util.DefaultXmlSymbolTable was unintentionally initialized at build time.

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Add native profile: native org.graalvm.buildtools native-maven-plugin build-native

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Add native profile: org.graalvm.buildtools native-maven-plugin native build-native

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Add native profile: com.github.asm0dey.botassistant.BotAssistantApplication bot-assistant target/native

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Add the --trace-class-initialization argument: Run native org.graalvm.buildtools native-maven-plugin build-native mvn -Pnative native:compile

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Add the --trace-class-initialization argument: Run --trace-class-initialization=com.ctc.wstx.util.DefaultXmlSymbolT bot-assistant target/native com.github.asm0dey.botassistant.BotAssistantApplication mvn -Pnative native:compile

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More detailed output: Error: Classes that should be initialized at run time got initialized during image building: com.ctc.wstx.api.CommonConfig was unintentionally initialized at build time. org.springframework.http.codec.xml.XmlEventDecoder caused initialization of this class with the following trace: at com.ctc.wstx.api.CommonConfig.(CommonConfig.java:59) at com.ctc.wstx.stax.WstxInputFactory.(WstxInputFactory.java:149) at java.lang.invoke.DirectMethodHandle$Holder.newInvokeSpecial(DirectMethodHandle$Holder) at java.lang.invoke.Invokers$Holder.invokeExact_MT(Invokers$Holder) at jdk.internal.reflect.DirectConstructorHandleAccessor.invokeImpl(DirectConstructorHandle at jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandl

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More detailed output: We found the culprit! org.springframework.http.codec.xml.XmlEventDecoder caused initialization of this class Error: Classes that should be initialized at run time got initialized during image building: com.ctc.wstx.api.CommonConfig was unintentionally initialized at build time. with the following trace: at com.ctc.wstx.api.CommonConfig.(CommonConfig.java:59) at com.ctc.wstx.stax.WstxInputFactory.(WstxInputFactory.java:149) at java.lang.invoke.DirectMethodHandle$Holder.newInvokeSpecial(DirectMethodHandle$Holder) at java.lang.invoke.Invokers$Holder.invokeExact_MT(Invokers$Holder) at jdk.internal.reflect.DirectConstructorHandleAccessor.invokeImpl(DirectConstructorHandle at jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandl

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Alright, let’s add the option to initialize org.springframework.http.codec.xml.XmlEventDecoder at runtime: Run native org.graalvm.buildtools native-maven-plugin build-native mvn -Pnative native:compile

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Alright, let’s add the option to initialize org.springframework.http.codec.xml.XmlEventDecoder at runtime: Run --initialize-at-run-time=org.springframework.http.codec.xml.XmlE bot-assistant target/native com.github.asm0dey.botassistant.BotAssistantApplication mvn -Pnative native:compile

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The same dragon! This is one evasive dragon… Error: Classes that should be initialized at run time got initialized during image building: com.ctc.wstx.api.CommonConfig was unintentionally initialized at build time. To see why com.ctc.w com.ctc.wstx.stax.WstxInputFactory was unintentionally initialized at build time. To see why com. com.ctc.wstx.api.ReaderConfig was unintentionally initialized at build time. To see why com.ctc.ws com.ctc.wstx.util.DefaultXmlSymbolTable was unintentionally initialized at build time. To see why To see how the classes got initialized, use --trace-class-initialization=com.ctc.wstx.api.CommonCo

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Apparently, another known issue ➡️ Need to add the --strict-image-heap option. This mode requires only the classes that are stored in the image heap to be marked with –initialize-at- build-time. This effectively reduces the number of configuration entries necessary to achieve build-time initialization. Note that --strict-image-heap is enabled by default in Native Image starting from GraalVM for JDK 22.

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Let’s add the --strict-image-heap option: Run --strict-image-heap bot-assistant target/native com.github.asm0dey.botassistant.BotAssistantApplication mvn -Pnative native:compile

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Success!

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Success! …Or is it?

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Success! …Or is it? The image was build, let’s run it.

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Another dragon! 2025-04-11T12:25:33.511+03:00 ERROR 64619 --- [bot-assistant] [nio-8081-exec-2] o.a.c.c.C.[.[.[/] java.lang.UnsatisfiedLinkError: jdk.jfr.internal.JVM.isExcluded(Ljava/lang/Class;)Z [symbol: Java_jdk_jfr_internal_JVM_isExcluded or Java_jdk_jfr_internal_JVM_isExcluded__Ljava_lang_Class_2] at org.graalvm.nativeimage.builder/com.oracle.svm.core.jni.access.JNINativeLinkage.getOrF at org.graalvm.nativeimage.builder/com.oracle.svm.core.jni.JNIGeneratedMethodSupport.nativ at [email protected]/jdk.jfr.internal.JVM.isExcluded(Native Method) ~[na:na] at [email protected]/jdk.jfr.internal.MetadataRepository.register(MetadataRepository

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Another dragon! Apparently, when we create a connection to Redis, Spring creates a custom JFR event java.lang.UnsatisfiedLinkError: jdk.jfr.internal.JVM.isExcluded(Ljava/lang/Class;)Z [symbol: Java_jdk_jfr_internal_JVM_isExcluded or Java_jdk_jfr_internal_JVM_isExcluded__Ljava_lang_Class_2] 2025-04-11T12:25:33.511+03:00 ERROR 64619 --- [bot-assistant] [nio-8081-exec-2] o.a.c.c.C.[.[.[/] at org.graalvm.nativeimage.builder/com.oracle.svm.core.jni.access.JNINativeLinkage.getOrF at org.graalvm.nativeimage.builder/com.oracle.svm.core.jni.JNIGeneratedMethodSupport.nativ at [email protected]/jdk.jfr.internal.JVM.isExcluded(Native Method) ~[na:na] at [email protected]/jdk.jfr.internal.MetadataRepository.register(MetadataRepository

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Even the Tracing Agent doesn’t detect that! So, let’s enable JFR explicitly: Run --enable-monitoring=jfr bot-assistant target/native com.github.asm0dey.botassistant.BotAssistantApplication --strict-image-heap mvn -Pnative native:compile

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Finally, everything works!

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Finally, everything works! …on my machine

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Let’s move on to building a native image in a Docker container.

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FROM bellsoft/liberica-native-image-kit-container:jdk-21-nik-23.1.6-musl as builder ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw -Pnative native:compile FROM bellsoft/alpaquita-linux-base:stream-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app ENTRYPOINT ["/app/app"] COPY --from=builder /app/${project}/target/native/${project} /app/app

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FROM bellsoft/liberica-native-image-kit-container:jdk-21-nik-23.1.6-musl as builder RUN cd ${project} && ./mvnw -Pnative native:compile ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ FROM bellsoft/alpaquita-linux-base:stream-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app ENTRYPOINT ["/app/app"] COPY --from=builder /app/${project}/target/native/${project} /app/app

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FROM bellsoft/alpaquita-linux-base:stream-musl ENTRYPOINT ["/app/app"] COPY --from=builder /app/${project}/target/native/${project} /app/app FROM bellsoft/liberica-native-image-kit-container:jdk-21-nik-23.1.6-musl as builder ARG project ENV project=${project} WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw -Pnative native:compile ARG project ENV project=${project} RUN apk add curl WORKDIR /app

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Another dragon! 2189.3 [6/8] Compiling methods... [*************] 2189.3 2189.3 Fatal error: org.graalvm.compiler.debug.GraalError: org.graalvm.compiler.core.common.PermanentBailoutException: Compilation exceeded 300.000000 seconds during CFG traversal 2189.3 at method: Future

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Another dragon! 2189.3 Fatal error: org.graalvm.compiler.debug.GraalError: org.graalvm.compiler.core.common.PermanentBailoutException: Compilation exceeded 300.000000 seconds during CFG traversal 2189.3 [6/8] Compiling methods... [*************] 2189.3 2189.3 at method: Future

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The build was taking too long and never finished Solution: Increase timeout time Build the image on a powerful PC or in the CI Plug a laptop into a power socket

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The build was taking too long and never finished Solution: Increase timeout time Build the image on a powerful PC or in the CI Plug a laptop into a power socket

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The build was taking too long and never finished Solution: Increase timeout time Build the image on a powerful PC or in the CI Plug a laptop into a power socket Let's give it another try!

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Another dragon! 520.7 [8/8] Creating image... [*****] 520.7 --------------------------------------------------------------------------------------------- 520.7 53.2s (13.5% of total time) in 2385 GCs | Peak RSS: 6.77GB | CPU load: 520.7 --------------------------------------------------------------------------------------------- 520.7 Produced artifacts: 520.7 /app/bot-assistant/target/native/svm_err_b_20250415T153317.420_pid287.md (build_info) 520.7 ============================================================================================= 520.7 Failed generating 'bot' after 6m 32s. 520.7 520.7 The build process encountered an unexpected error: 520.7

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Another dragon! 520.7 The build process encountered an unexpected error: 520.7 > java.lang.RuntimeException: There was an error linking the native image: Linker command exited with 1 520.7 ============================================================================================ 520.7 Failed generating 'bot' after 6m 32s. 520.7 520.7 520.7 520.7 Linker command executed: 520.7 /usr/bin/gcc -z noexecstack -Wl,--gc-sections -Wl,--version-script,/tmp/SVM-1092355479500053 520.7

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Linking issue: musl libc lacks required tools Option 1: add required packages (libstc++, etc.) with apk add Option 2: switch from musl-based Alpaquita to glibc-based FROM bellsoft/liberica-native-image-kit-container:jdk-21-nik-23.1.6-stream-musl as builder WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw -Pnative native:compile FROM bellsoft/alpaquita-linux-base:stream-musl ARG project ENV project=${project} RUN apk add curl WORKDIR /app

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Linking issue: musl libc lacks required tools Option 1: add required packages (libstc++, etc.) with apk add Option 2: switch from musl-based Alpaquita to glibc-based FROM bellsoft/liberica-native-image-kit-container:jdk-21-nik-23.1.6-stream-glibc as builder WORKDIR /app ADD ${project} /app/${project} ADD ../pom.xml ./ RUN cd ${project} && ./mvnw -Pnative native:compile FROM bellsoft/alpaquita-linux-base:stream-glibc ARG project ENV project=${project} RUN apk add curl WORKDIR /app

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We did it!

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We did it! Both services compile and run successfully

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We need drastic changes, I won’t settle for half-measures! The Rebel

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Coordinated Restore at Checkpoint (CRaC) The CRaC (Coordinated Restore at Checkpoint) Project researches coordination of Java programs with mechanisms to checkpoint (make an image of, snapshot) a Java instance while it is executing. Restoring from the image could be a solution to some of the problems with the start-up and warm-up times. The primary aim of the Project is to develop a new standard mechanism-agnostic API to notify Java programs about the checkpoint and restore events. Other research activities will include, but will not be limited to, integration with existing checkpoint/restore mechanisms and development of new ones, changes to JVM and JDK to make images smaller and ensure they are correct. https://openjdk.org/projects/crac/

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TL;DR Pause and restart a Java application A snapshot of the current JVM state JVM is still there: dynamic performance optimization is possible after restore

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CRaC is not a canonical part of JDK Only some vendors provide it: BellSoft, Azul Azul was the first to implement, BellSoft supports a fork

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Project CRaC: Any Considerations? A snapshot may contain sensitive data May need to augment the code for reliable checkpoint and restore

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Trivial example public static void main(String args[]) throws InterruptedException { // This is a part of the saved state long startTime = System.currentTimeMillis(); for(int counter: IntStream.range(1, 10000).toArray()) { Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); startTime = currentTime; } }

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Trivial example // This is a part of the saved state public static void main(String args[]) throws InterruptedException { long startTime = System.currentTimeMillis(); for(int counter: IntStream.range(1, 10000).toArray()) { Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); startTime = currentTime; } }

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Trivial example long startTime = System.currentTimeMillis(); public static void main(String args[]) throws InterruptedException { // This is a part of the saved state for(int counter: IntStream.range(1, 10000).toArray()) { Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); startTime = currentTime; } }

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Trivial example for(int counter: IntStream.range(1, 10000).toArray()) { public static void main(String args[]) throws InterruptedException { // This is a part of the saved state long startTime = System.currentTimeMillis(); Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); startTime = currentTime; } }

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Trivial example Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); public static void main(String args[]) throws InterruptedException { // This is a part of the saved state long startTime = System.currentTimeMillis(); for(int counter: IntStream.range(1, 10000).toArray()) { startTime = currentTime; } }

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Trivial example startTime = currentTime; public static void main(String args[]) throws InterruptedException { // This is a part of the saved state long startTime = System.currentTimeMillis(); for(int counter: IntStream.range(1, 10000).toArray()) { Thread.sleep(1000); long currentTime = System.currentTimeMillis(); System.out.println("Counter: " + counter + "(passed " + (currentTime-startTime) + " ms)"); } }

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Docker… FROM bellsoft/liberica-runtime-container:jdk-crac-slim ADD Example.java /app/Example.java WORKDIR /app RUN javac Example.java ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example

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Docker… ...is not that simple FROM bellsoft/liberica-runtime-container:jdk-crac-slim ADD Example.java /app/Example.java WORKDIR /app RUN javac Example.java ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example

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Docker… ...is not that simple ADD Example.java /app/Example.java FROM bellsoft/liberica-runtime-container:jdk-crac-slim WORKDIR /app RUN javac Example.java ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example

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Docker… ...is not that simple RUN javac Example.java FROM bellsoft/liberica-runtime-container:jdk-crac-slim ADD Example.java /app/Example.java WORKDIR /app ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example

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Docker… ...is not that simple ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example FROM bellsoft/liberica-runtime-container:jdk-crac-slim ADD Example.java /app/Example.java WORKDIR /app RUN javac Example.java

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Docker… ...is not that simple This does not create the checkpoint yet! ENTRYPOINT java -XX:CRaCCheckpointTo=/app/checkpoint Example FROM bellsoft/liberica-runtime-container:jdk-crac-slim ADD Example.java /app/Example.java WORKDIR /app RUN javac Example.java

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And then

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And then Build it docker build -t pre_crack -f crac2/Dockerfile crac2

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run -d pre_crack

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run -d pre_crack # will fail

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --privileged -d pre_crack

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --privileged -d pre_crack # will work, but security folks will hate us

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -d pre_crack

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And then Build it Run it docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -d pre_crack # Not so frightening if you think about it

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And then Build it Run it CAP_SYS_PTRACE : we need to access the whole process tree transfer data to or from the memory of arbitrary processes using process_vm_readv(2) and process_vm_writev(2) docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -d pre_crack # Not so frightening if you think about it

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And then Build it Run it CAP_SYS_PTRACE : we need to access the whole process tree transfer data to or from the memory of arbitrary processes using process_vm_readv(2) and process_vm_writev(2) CAP_CHECKPOINT_RESTORE : somehow there is a special cap for this Update /proc/sys/kernel/ns_last_pid ; Read the contents of the symbolic links in /proc/pid/map_files for other processes docker build -t pre_crack -f crac2/Dockerfile crac2 docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -d pre_crack # Not so frightening if you think about it

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And then Checkpoint it ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint docker commit $ID cracked docker run --rm -d \ --entrypoint java \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Checkpoint it # wait some time ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac docker exec -it $ID jcmd 129 JDK.checkpoint docker commit $ID cracked docker run --rm -d \ --entrypoint java \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Checkpoint it docker exec -it $ID jcmd 129 JDK.checkpoint ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker commit $ID cracked docker run --rm -d \ --entrypoint java \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Checkpoint it docker commit $ID cracked ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint docker run --rm -d \ --entrypoint java \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Now we’re ready! Checkpoint it docker commit $ID cracked ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint docker run --rm -d \ --entrypoint java \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Now we’re ready! Checkpoint it docker commit $ID cracked ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint --entrypoint java \ docker run --rm -d \ --network host cracked:latest \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Now we’re ready! Checkpoint it docker commit $ID cracked ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint --network host cracked:latest \ docker run --rm -d \ --entrypoint java \ -XX:CRaCRestoreFrom=/app/checkpoint

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And then Now we’re ready! Checkpoint it docker commit $ID cracked ID=$(docker run --cap-add CAP_SYS_PTRACE --cap-add CAP_CHECKPOINT_RESTORE -p8080:8080 -d pre_crac # wait some time docker exec -it $ID jcmd 129 JDK.checkpoint -XX:CRaCRestoreFrom=/app/checkpoint docker run --rm -d \ --entrypoint java \ --network host cracked:latest \

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And it just works!

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And it just works! Until it doesn't

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In our startup

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In our startup bot-assistant module just works chat-api doesn’t work!

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In our startup bot-assistant module just works chat-api doesn’t work! Only some projects are guaranteed to work.

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In our startup bot-assistant module just works chat-api doesn’t work! Only some projects are guaranteed to work. Others… Request support from the team: is not supported for now :(

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What are the options?

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What are the options? Fall back to another solution

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What are the options? Fall back to another solution Request support

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What are the options? Fall back to another solution Request support Implement support on our own!

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Implementing support on our own. Custom MongoClient public class MongoClientProxy implements MongoClient { volatile MongoClient delegate; public MongoClientProxy(MongoClient initialClient) { this.delegate = initialClient; } public void close() { delegate.close(); } // Delegate everything else the same way

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Implementing support on our own. Custom MongoClient volatile MongoClient delegate; public MongoClientProxy(MongoClient initialClient) { this.delegate = initialClient; } public class MongoClientProxy implements MongoClient { public void close() { delegate.close(); } // Delegate everything else the same way

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Implementing support on our own. Custom MongoClient public void close() { delegate.close(); } public class MongoClientProxy implements MongoClient { volatile MongoClient delegate; public MongoClientProxy(MongoClient initialClient) { this.delegate = initialClient; } // Delegate everything else the same way

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Implementing support on our own. Custom MongoClient // Delegate everything else the same way public class MongoClientProxy implements MongoClient { volatile MongoClient delegate; public MongoClientProxy(MongoClient initialClient) { this.delegate = initialClient; } public void close() { delegate.close(); }

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Implementing support on our own Custom CRaC Resource @Component static public class MongoClientResource implements Resource { private final MongoClientProxy mongoClientProxy; private final MongoConnectionDetails details; public MongoClientResource(MongoClient mongoClientProxy, MongoConnectionDetails details) { this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; this.details = details; Core.getGlobalContext().register(this); } @Override public void beforeCheckpoint(Context context) {

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Implementing support on our own Custom CRaC Resource public MongoClientResource(MongoClient mongoClientProxy, MongoConnectionDetails details) { this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; this.details = details; Core.getGlobalContext().register(this); } static public class MongoClientResource implements Resource { private final MongoClientProxy mongoClientProxy; private final MongoConnectionDetails details; @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); }

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Implementing support on our own Custom CRaC Resource private final MongoClientProxy mongoClientProxy; this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; @Component static public class MongoClientResource implements Resource { private final MongoConnectionDetails details; public MongoClientResource(MongoClient mongoClientProxy, MongoConnectionDetails details) { this.details = details; Core.getGlobalContext().register(this); } @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close();

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Implementing support on our own Custom CRaC Resource private final MongoConnectionDetails details; this.details = details; static public class MongoClientResource implements Resource { private final MongoClientProxy mongoClientProxy; public MongoClientResource(MongoClient mongoClientProxy, MongoConnectionDetails details) { this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; Core.getGlobalContext().register(this); } @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); }

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Implementing support on our own Custom CRaC Resource Core.getGlobalContext().register(this); private final MongoClientProxy mongoClientProxy; private final MongoConnectionDetails details; public MongoClientResource(MongoClient mongoClientProxy, MongoConnectionDetails details) { this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; this.details = details; } @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); }

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Implementing support on our own Custom CRaC Resource @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); } this.mongoClientProxy = (MongoClientProxy) mongoClientProxy; this.details = details; Core.getGlobalContext().register(this); } @Override public void afterRestore(Context context) { mongoClientProxy.delegate = MongoClients.create(details.getConnectionString()); } }

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Implementing support on our own Custom CRaC Resource @Override public void afterRestore(Context context) { mongoClientProxy.delegate = MongoClients.create(details.getConnectionString()); } this.details = details; Core.getGlobalContext().register(this); } @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); } }

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Implementing support on our own Custom CRaC Resource mongoClientProxy.delegate = MongoClients.create(details.getConnectionString()); this.details = details; Core.getGlobalContext().register(this); } @Override public void beforeCheckpoint(Context context) { mongoClientProxy.delegate.close(); } @Override public void afterRestore(Context context) { } }

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Implementing support on our own Replacing MongoClient in the context @Bean public MongoClient mongoClient(MongoConnectionDetails details) { @Primary MongoClient initialClient = MongoClients.create(details.getConnectionString()); return new MongoClientProxy(initialClient); }

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Implementing support on our own Replacing MongoClient in the context MongoClient initialClient = MongoClients.create(details.getConnectionString()); @Bean @Primary public MongoClient mongoClient(MongoConnectionDetails details) { return new MongoClientProxy(initialClient); }

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Implementing support on our own Replacing MongoClient in the context @Primary return new MongoClientProxy(initialClient); @Bean public MongoClient mongoClient(MongoConnectionDetails details) { MongoClient initialClient = MongoClients.create(details.getConnectionString()); }

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And they all lived happily ever after!

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Quick Recap 🛡 → AppCDS for the smoothest integration 🧙‍♂️ → Project Leyden EA builds to prepare to use it in the future 🎒 → Native Image for fast start ✊🏼 → CRaC for almost instant start Testing locally? Use a power cord! Which hero are you?

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This story came to an end, yours has just begun Go for it!

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Thank you for your attention! @asm0dey.site @cat-edelveis.bsky.social asm0di0 cat_edelveis Find us at