背景

早期我们对于 Docker 构建 Spring Boot 工程的方式很简单，直接构建生成 jar 可执行程序，通过 java $JAVA_OPTS -jar 启动。在 Kubernetes 环境下，如果要调整 JVM 参数，则通过 ConfigMap 维护 JAVA_OPTS 变量，方便统一管理同一个 Nacos 配置中心，如下：

-Xmn1G
-Xmx1G
-Xss256k
-Dspring.cloud.nacos.config.username=nacos 
-Dspring.cloud.nacos.config.password=nacos
-Dspring.cloud.nacos.config.server-addr=127.0.0.1:8848

在实际的生产环境，可能定义了十几个甚至上百个 Deployment，每个 Deployment 根据不同的负载设置不同的 JVM 参数，没办法共享同一份 ConfigMap 文件。为了解决这个问题，我们应该优化下 Dockerfile 构建模板，把 JVM 参数和运行环境变量分离出去。

目标

制定一套标准 Docker 构建模板，简化 JVM 配置流程。

实现

首先从 Dockerfile 文件着手，需要考虑几个方面：

镜像分层：分离基础镜像（固定）、辅助工具（固定）、Maven 依赖（基本不变）和应用程序代码（变化），并减少镜像体积，通过镜像缓存提高构建速度。
变量简化：提取研发团队比较关心的 JVM 参数作为环境变量，例如 XMS 最小堆、XMX 最大堆、XSS 线程栈、GC 模式、GC 日志、堆转储、开启大页内存等。
容器安全：基于最小权限原则，运行容器时，以非 root 用户运行，只允许持有特定目录的读写权限。
脚本分离：将启动脚本与 Dockerfile 分离，方便从 ConfigMap 维护。

Dockerfile 内容如下，因 DockerHub 镜像仓库访问不稳定，代码使用了 m.daocloud.io 代理，您可以根据实际情况调整。

# 使用基础镜像
FROM m.daocloud.io/eclipse-temurin:11-jdk-alpine AS builder

# 指定构建模块
ARG MODULE=eden-demo-cola-start

# 设置工作目录
WORKDIR /app

# 复制必要文件
COPY $MODULE/target/$MODULE.jar application.jar
COPY docker/entrypoint.sh entrypoint.sh

# 安装最小依赖项
RUN sed -i 's|https://dl-cdn.alpinelinux.org|https://mirrors.aliyun.com|g' /etc/apk/repositories \
	&& apk update \
	&& apk add --no-cache tar binutils dos2unix \
    && dos2unix entrypoint.sh \
    && jdeps --ignore-missing-deps -q \
		--recursive \
		--multi-release 11 \
		--print-module-deps \
		--class-path '/BOOT-INF/lib/*' \
		application.jar > modules.txt

# 构建运行环境
RUN $JAVA_HOME/bin/jlink \
		--verbose \
		--add-modules $(cat modules.txt),sun.misc \
		--strip-debug \
		--no-man-pages \
		--no-header-files \
		--compress=2 \
		--output /jre

# 使用 Spring Boot 的分层模式提取 JAR 文件的依赖项
RUN java -Djarmode=layertools -jar application.jar extract

# 创建容器镜像
FROM m.daocloud.io/alpine:latest

# 定义元数据
LABEL maintainer="梦想歌 <shiyindaxiaojie@gmail.com>"
LABEL version="1.0.0"

# 指定构建参数
ARG USER=tmpuser
ARG GROUP=tmpgroup

# 设置环境变量
ENV JAVA_HOME /opt/jdk/jdk-11
ENV PATH "${JAVA_HOME}/bin:${PATH}"
ENV HOME "/app"
ENV TZ "Asia/Shanghai"
ENV LANG "C.UTF-8"
ENV XMS "1g"
ENV XMX "1g"
ENV XSS "256k"
ENV GC_MODE "G1"
ENV USE_GC_LOG "Y"
ENV USE_HEAP_DUMP "Y"
ENV USE_LARGE_PAGES "N"
ENV SPRING_PROFILES_ACTIVE "dev"
ENV SERVER_PORT "8080"
ENV MANAGEMENT_SERVER_PORT "9080"

# 设置日志目录
RUN mkdir -p $HOME/logs \
	&& touch $HOME/logs/entrypoint.out \
	&& ln -sf /dev/stdout $HOME/logs/entrypoint.out \
	&& ln -sf /dev/stderr $HOME/logs/entrypoint.out

# 切换工作目录
WORKDIR $HOME

# 从基础镜像复制应用程序依赖项和模块
COPY --from=builder /jre $JAVA_HOME
COPY --from=builder /app/dependencies/ ./
COPY --from=builder /app/spring-boot-loader ./
COPY --from=builder /app/organization-dependencies ./
COPY --from=builder /app/modules-dependencies ./
COPY --from=builder /app/snapshot-dependencies/ ./
COPY --from=builder /app/application/ ./
COPY --from=builder /app/entrypoint.sh ./

# 创建普通用户
RUN addgroup -g 1000 $GROUP \
	&& adduser -u 1000 -G $GROUP -h $HOME -s /bin/bash -D $USER \
	&& chown -R $USER:$GROUP $HOME \
	&& chmod -R a+rwX $HOME

# 切换到容器用户
USER $USER

# 暴露容器端口
EXPOSE $SERVER_PORT $MANAGEMENT_SERVER_PORT

# 设置启动脚本
CMD ["./entrypoint.sh"]

笔者将启动脚本命名为 entrypoint.sh，内容如下：

#!/bin/sh

JAVA_MAJOR_VERSION=$(java -version 2>&1 | sed -E -n 's/.* version "([0-9]*).*$/\1/p')

JAVA_OPTS="${JAVA_OPTS} -server"
JAVA_OPTS="${JAVA_OPTS} -XX:+UnlockExperimentalVMOptions -XX:+UnlockDiagnosticVMOptions"
JAVA_OPTS="${JAVA_OPTS} -XX:+AlwaysPreTouch -XX:+PrintFlagsFinal -XX:-DisplayVMOutput -XX:-OmitStackTraceInFastThrow"
JAVA_OPTS="${JAVA_OPTS} -Xms${XMS:-1G} -Xmx${XMX:-1G} -Xss${XSS:-256K}"
JAVA_OPTS="${JAVA_OPTS} -XX:MetaspaceSize=${METASPACE_SIZE:-128M} -XX:MaxMetaspaceSize=${MAX_METASPACE_SIZE:-256M}"
JAVA_OPTS="${JAVA_OPTS} -XX:MaxGCPauseMillis=${MAX_GC_PAUSE_MILLIS:-200}"

if [ "${GC_MODE}" = "ShenandoahGC" ]; then
    echo "GC mode is ShenandoahGC"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseShenandoahGC"
elif [ "${GC_MODE}" = "ZGC" ]; then
    echo "GC mode is ZGC"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseZGC"
elif [ "${GC_MODE}" = "G1" ]; then
    echo "GC mode is G1"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseG1GC"
    JAVA_OPTS="${JAVA_OPTS} -XX:InitiatingHeapOccupancyPercent=${INITIATING_HEAP_OCCUPANCY_PERCENT:-45}"
    JAVA_OPTS="${JAVA_OPTS} -XX:G1ReservePercent=${G1_RESERVE_PERCENT:-10} -XX:G1HeapWastePercent=${G1_HEAP_WASTE_PERCENT:-5} "
    JAVA_OPTS="${JAVA_OPTS} -XX:G1NewSizePercent=${G1_NEW_SIZE_PERCENT:-50} -XX:G1MaxNewSizePercent=${G1_MAX_NEW_SIZE_PERCENT:-50}"
    JAVA_OPTS="${JAVA_OPTS} -XX:G1MixedGCCountTarget=${G1_MIXED_GCCOUNT_TARGET:-8}"
    JAVA_OPTS="${JAVA_OPTS} -XX:G1MixedGCLiveThresholdPercent=${G1_MIXED_GCLIVE_THRESHOLD_PERCENT:-65}"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseStringDeduplication -XX:+ParallelRefProcEnabled"
elif [ "${GC_MODE}" = "CMS" ]; then
    echo "GC mode is CMS"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseConcMarkSweepGC -Xmn${XMN:-512m}"
    JAVA_OPTS="${JAVA_OPTS} -XX:ParallelGCThreads=${PARALLEL_GC_THREADS:-2} -XX:ConcGCThreads=${CONC_GC_THREADS:-1}"
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseCMSInitiatingOccupancyOnly -XX:CMSInitiatingOccupancyFraction=${CMS_INITIATING_HEAP_OCCUPANCY_PERCENT:-92}"
    JAVA_OPTS="${JAVA_OPTS} -XX:+CMSClassUnloadingEnabled -XX:+CMSScavengeBeforeRemark"
    if [ "$JAVA_MAJOR_VERSION" -le "8" ] ; then
        JAVA_OPTS="${JAVA_OPTS} -XX:+CMSIncrementalMode -XX:CMSFullGCsBeforeCompaction=${CMS_FULL_GCS_BEFORE_COMPACTION:-5}"
        JAVA_OPTS="${JAVA_OPTS} -XX:+ExplicitGCInvokesConcurrent -XX:+ExplicitGCInvokesConcurrentAndUnloadsClasses"
    fi
fi

if [ "${USE_GC_LOG}" = "Y" ]; then
    echo "GC log path is '${HOME}/logs/jvm_gc.log'."
    JAVA_OPTS="${JAVA_OPTS} -XX:+PrintVMOptions"
    if [ "$JAVA_MAJOR_VERSION" -gt "8" ] ; then
        JAVA_OPTS="${JAVA_OPTS} -Xlog:gc:file=${HOME}/logs/jvm_gc-%p-%t.log:tags,uptime,time,level:filecount=${GC_LOG_FILE_COUNT:-10},filesize=${GC_LOG_FILE_SIZE:-100M}"
    else
        JAVA_OPTS="${JAVA_OPTS} -Xloggc:${HOME}/logs/jvm_gc.log -verbose:gc -XX:+PrintGCDetails -XX:+PrintGCDateStamps -XX:+PrintGCTimeStamps"
        JAVA_OPTS="${JAVA_OPTS} -XX:+UseGCLogFileRotation -XX:NumberOfGCLogFiles=${GC_LOG_FILE_COUNT:-10} -XX:GCLogFileSize=${GC_LOG_FILE_SIZE:-100M}"
        JAVA_OPTS="${JAVA_OPTS} -XX:+PrintGCCause -XX:+PrintGCApplicationStoppedTime"
        JAVA_OPTS="${JAVA_OPTS} -XX:+PrintTLAB -XX:+PrintReferenceGC -XX:+PrintHeapAtGC"
        JAVA_OPTS="${JAVA_OPTS} -XX:+FlightRecorder -XX:+PrintSafepointStatistics -XX:PrintSafepointStatisticsCount=1"
        JAVA_OPTS="${JAVA_OPTS} -XX:+DebugNonSafepoints -XX:+SafepointTimeout -XX:SafepointTimeoutDelay=500"
    fi
fi

if [ ! -d "${HOME}/logs" ]; then
    mkdir ${HOME}/logs
fi

if [ "${USE_HEAP_DUMP}" = "Y" ]; then
    echo "Heap dump path is '${HOME}/logs/jvm_heap_dump.hprof'."
    JAVA_OPTS="${JAVA_OPTS} -XX:HeapDumpPath=${HOME}/logs/jvm_heap_dump.hprof -XX:+HeapDumpOnOutOfMemoryError"
fi

if [ "${USE_LARGE_PAGES}" = "Y" ]; then
    echo "Use large pages."
    JAVA_OPTS="${JAVA_OPTS} -XX:+UseLargePages"
fi

if [ "${JDWP_DEBUG:-N}" = "Y" ]; then
    echo "Attach to remote JVM using port ${JDWP_PORT:-5005}."
    JAVA_OPTS="${JAVA_OPTS} -Xdebug -Xrunjdwp:transport=dt_socket,address=${JDWP_PORT:-5005},server=y,suspend=n"
fi

JAVA_OPTS="${JAVA_OPTS} -Dserver.port=${SERVER_PORT} -Dmanagement.server.port=${MANAGEMENT_SERVER_PORT}"

exec java $JAVA_OPTS -noverify -Djava.security.egd=file:/dev/./urandom "org.springframework.boot.loader.JarLauncher" "$@"