Dockerfiles

雖然可以僅在 Dockerfile 中使用幾行程式碼將 Spring Boot uber jar 轉換為 Docker 映像檔，但使用分層功能將產生最佳化的映像檔。當您建立包含圖層索引檔案的 jar 時，spring-boot-jarmode-tools jar 將作為依賴項新增至您的 jar。將此 jar 放在類別路徑中，您可以使用特殊模式啟動應用程式，讓引導程式碼執行與應用程式完全不同的操作，例如，提取圖層的操作。

`tools` 模式不能與包含啟動腳本的完全可執行的 Spring Boot 歸檔檔一起使用。在建置旨在與 layertools 一起使用的 jar 檔案時，請停用啟動腳本組態。

以下說明如何使用 tools jar 模式啟動 jar

$ java -Djarmode=tools -jar my-app.jar

這將提供以下輸出

Usage:
  java -Djarmode=tools -jar my-app.jar

Available commands:
  extract      Extract the contents from the jar
  list-layers  List layers from the jar that can be extracted
  help         Help about any command

`extract` 命令可用於輕鬆地將應用程式分割成圖層，以新增至 Dockerfile。以下是使用 jarmode 的 Dockerfile 範例。

# 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/ ./
# 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
ENTRYPOINT ["java", "-jar", "application.jar"]

假設上述 Dockerfile 位於目前目錄中，您的 Docker 映像檔可以使用 docker build . 建置，或者選擇性地指定應用程式 jar 的路徑，如下列範例所示

$ docker build --build-arg JAR_FILE=path/to/myapp.jar .

這是一個多階段 Dockerfile。建置器階段提取稍後需要的目錄。每個 COPY 命令都與 jarmode 提取的圖層相關。

當然，可以編寫 Dockerfile 而不使用 jarmode。您可以使用 unzip 和 mv 的某種組合將內容移動到正確的圖層，但 jarmode 簡化了這一點。此外，jarmode 建立的佈局開箱即用即 CDS 友善。

CDS

如果您還想啟用 CDS，可以使用此 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/ ./
# 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"]

這與上述 Dockerfile 大致相同。作為最後步驟，它透過執行訓練執行來建立 CDS 歸檔檔，並將 CDS 參數傳遞給 java -jar。