64 lines
2.7 KiB
Plaintext
64 lines
2.7 KiB
Plaintext
[[container-images.dockerfiles]]
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== Dockerfiles
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While it is possible to convert a Spring Boot fat jar into a docker image with just a few lines in the Dockerfile, we will use the <<container-images#container-images.efficient-images.layering,layering feature>> to create an optimized docker image.
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When you create a jar containing the layers index file, the `spring-boot-jarmode-layertools` jar will be added as a dependency to your jar.
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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.
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CAUTION: The `layertools` mode can not be used with a <<deployment#deployment.installing, fully executable Spring Boot archive>> that includes a launch script.
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Disable launch script configuration when building a jar file that is intended to be used with `layertools`.
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Here’s how you can launch your jar with a `layertools` jar mode:
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[source,shell,indent=0,subs="verbatim"]
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----
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$ java -Djarmode=layertools -jar my-app.jar
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----
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This will provide the following output:
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[subs="verbatim"]
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----
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Usage:
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java -Djarmode=layertools -jar my-app.jar
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Available commands:
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list List layers from the jar that can be extracted
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extract Extracts layers from the jar for image creation
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help Help about any command
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----
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The `extract` command can be used to easily split the application into layers to be added to the dockerfile.
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Here is an example of a Dockerfile using `jarmode`.
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[source,dockerfile,indent=0,subs="verbatim"]
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----
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FROM eclipse-temurin:17-jre as builder
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WORKDIR application
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ARG JAR_FILE=target/*.jar
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COPY ${JAR_FILE} application.jar
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RUN java -Djarmode=layertools -jar application.jar extract
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FROM eclipse-temurin:17-jre
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WORKDIR application
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COPY --from=builder application/dependencies/ ./
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COPY --from=builder application/spring-boot-loader/ ./
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COPY --from=builder application/snapshot-dependencies/ ./
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COPY --from=builder application/application/ ./
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ENTRYPOINT ["java", "org.springframework.boot.loader.JarLauncher"]
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----
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Assuming the above `Dockerfile` is in the current directory, your docker image can be built with `docker build .`, or optionally specifying the path to your application jar, as shown in the following example:
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[source,shell,indent=0,subs="verbatim"]
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----
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$ docker build --build-arg JAR_FILE=path/to/myapp.jar .
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----
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This is a multi-stage dockerfile.
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The builder stage extracts the directories that are needed later.
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Each of the `COPY` commands relates to the layers extracted by the jarmode.
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Of course, a Dockerfile can be written without using the jarmode.
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You can use some combination of `unzip` and `mv` to move things to the right layer but jarmode simplifies that.
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