云原生 Java：GraalVM 原生镜像、镜像瘦身与 Serverless

# 构建原生镜像（关键参数）
native-image -jar app.jar \
  -H:ReflectionConfigurationResources=reflect-config.json \
  -H:ResourceConfigurationResources=resource-config.json \
  -H:JNIConfigurationResources=jni-config.json \
  --no-fallback \
  --enable-url-protocols=https \
  -o myapp

# Spring Boot 3.3+ 一行构建原生镜像
./mvnw -Pnative native:compile

# 自动收集反射/资源配置：
# spring-boot-starter-parent 的 native 插件会在构建期扫描
# @ConfigurationProperties 绑定、@EnableXxx、SPI 加载点自动登记

<!-- Quarkus 核心：quarkus-maven-plugin 负责构建期处理 -->
<dependency>
    <groupId>io.quarkus</groupId>
    <artifactId>quarkus-resteasy-reactive</artifactId>
</dependency>

# Quarkus 原生镜像构建（内置 GraalVM 集成）
./mvnw package -Pnative -Dquarkus.native.container-build=true

# 阶段一：Maven 构建（体积大，不进入最终镜像）
FROM maven:3.9-eclipse-temurin-21 AS builder
WORKDIR /app
COPY pom.xml .
RUN mvn -B dependency:go-offline
COPY src ./src
RUN mvn -B -Pnative package

# 阶段二：运行时镜像（只带运行产物）
FROM eclipse-temurin:21-jre-jammy
RUN useradd -m -u 10001 appuser \
    && mkdir /app && chown appuser /app
USER appuser
COPY --from=builder /app/target/app.jar /app/app.jar
EXPOSE 8080
ENTRYPOINT ["java", "-XX:MaxRAMPercentage=70", "-jar", "/app/app.jar"]

# 阶段一：构建 jar
FROM maven:3.9-eclipse-temurin-21 AS builder
WORKDIR /app
COPY pom.xml .
RUN mvn -B dependency:go-offline
COPY src ./src
RUN mvn -B package -DskipTests

# 阶段二：distroless（无 shell、无包管理器，攻击面最小）
FROM gcr.io/distroless/java21-debian12
COPY --from=builder /app/target/app.jar /app/app.jar
USER nonroot
EXPOSE 8080
ENTRYPOINT ["java", "-XX:MaxRAMPercentage=70", "-jar", "/app/app.jar"]

# 列出应用用到的模块
jdeps --print-module-deps --ignore-missing-deps app.jar
# 输出例如：java.base,java.logging,java.sql,java.naming,jdk.unsupported

# 生成最小运行时
jlink \
  --add-modules java.base,java.logging,java.sql,java.naming,jdk.unsupported \
  --output /opt/min-jre \
  --strip-debug \
  --no-man-pages \
  --no-header-files \
  --compress=zip-6

# 用裁剪后的运行时构建镜像（体积从 180M → 80M）
FROM eclipse-temurin:21-jre AS jre-builder
RUN jlink --add-modules java.base,java.logging,java.sql \
    --output /opt/min-jre --strip-debug --no-man-pages \
    --no-header-files --compress=zip-6

FROM debian:bookworm-slim
COPY --from=jre-builder /opt/min-jre /opt/min-jre
COPY app.jar /app/app.jar
ENTRYPOINT ["/opt/min-jre/bin/java", "-jar", "/app/app.jar"]

# 利用 Spring Boot 3 内置分层（layertools），把依赖层与业务层分离，加速 CI 缓存
FROM eclipse-temurin:21-jre AS builder
COPY app.jar /app.jar
RUN java -Djarmode=layertools -jar /app.jar extract --destination /extracted

FROM gcr.io/distroless/java21-debian12
COPY --from=builder /extracted/dependencies/ /app/
COPY --from=builder /extracted/spring-boot-loader/ /app/
COPY --from=builder /extracted/snapshot-dependencies/ /app/
COPY --from=builder /extracted/application/ /app/
ENTRYPOINT ["java", "-jar", "/app/app.jar"]

# Deployment：JVM 参数使用 MaxRAMPercentage，随容器内存自适应
apiVersion: apps/v1
kind: Deployment
metadata:
  name: order-service
spec:
  replicas: 3
  template:
    spec:
      containers:
        - name: order
          image: registry/order-service:1.4.0
          resources:
            requests:
              memory: 1Gi
              cpu: 500m
            limits:
              memory: 1Gi        # 容器内存上限
          env:
            - name: JAVA_OPTS
              value: >-
                -XX:MaxRAMPercentage=70
                -XX:InitialRAMPercentage=50
                -XX:+UseContainerSupport
                -Xlog:gc*:file=/dev/stdout
          readinessProbe:
            httpGet: { path: /actuator/health/readiness, port: 8080 }
            initialDelaySeconds: 5
          livenessProbe:
            httpGet: { path: /actuator/health/liveness, port: 8080 }
---
# HPA：按 CPU/内存/自定义指标伸缩
apiVersion: autoscaling/v2
kind: HorizontalPodAutoscaler
metadata:
  name: order-service-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: order-service
  minReplicas: 2
  maxReplicas: 20
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 60
    - type: Resource
      resource:
        name: memory
        target:
          type: Utilization
          averageUtilization: 70

# Knative Service：min-scale 0 表示无请求即缩到零
apiVersion: serving.knative.dev/v1
kind: Service
metadata:
  name: report-service
spec:
  template:
    spec:
      containerConcurrency: 20      # 每 Pod 并发上限
      timeoutSeconds: 300
      containers:
        - image: registry/report-service:native
          env:
            - name: JAVA_OPTS
              value: "-XX:MaxRAMPercentage=70"
---
# Autoscaler 参数
# - concurrency-based：按并发自动扩缩
# - 缩到零延迟默认 30s 无流量即缩零

// 原生镜像下「懒初始化」示例：把重初始化放到首次调用
@Component
public class LazyInitializer {
    private volatile HeavyComponent heavy;

    public HeavyComponent getHeavy() {
        HeavyComponent local = heavy;
        if (local == null) {
            synchronized (this) {
                if (heavy == null) {
                    heavy = HeavyComponent.load();   // 构建期不可完成的初始化
                }
                local = heavy;
            }
        }
        return local;
    }
}