Java Spring Boot auf Kubernetes containerisieren

# Build Stage
FROM eclipse-temurin:21-jdk-alpine AS builder
WORKDIR /app
COPY gradle/ gradle/
COPY gradlew build.gradle.kts settings.gradle.kts ./
RUN ./gradlew dependencies --no-daemon
COPY src/ src/
RUN ./gradlew bootJar --no-daemon -x test

# Runtime Stage
FROM eclipse-temurin:21-jre-alpine
RUN addgroup -S appgroup && adduser -S appuser -G appgroup
WORKDIR /app
COPY --from=builder /app/build/libs/*.jar app.jar
USER appuser
EXPOSE 8080

ENTRYPOINT ["java", \
  "-XX:MaxRAMPercentage=75.0", \
  "-XX:InitialRAMPercentage=50.0", \
  "-XX:+UseG1GC", \
  "-jar", "app.jar"]

{/* pom.xml */}
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-actuator</artifactId>
</dependency>

management:
  endpoints:
    web:
      exposure:
        include: health,info,prometheus
  endpoint:
    health:
      probes:
        enabled: true
      show-details: always
  health:
    livenessState:
      enabled: true
    readinessState:
      enabled: true

apiVersion: apps/v1
kind: Deployment
metadata:
  name: spring-app
  labels:
    app: spring-app
spec:
  replicas: 2
  selector:
    matchLabels:
      app: spring-app
  strategy:
    type: RollingUpdate
    rollingUpdate:
      maxUnavailable: 0
      maxSurge: 1
  template:
    metadata:
      labels:
        app: spring-app
    spec:
      containers:
        - name: spring-app
          image: registry.example.com/spring-app:1.0.0
          ports:
            - containerPort: 8080
          resources:
            requests:
              memory: "512Mi"
              cpu: "250m"
            limits:
              memory: "512Mi"
              cpu: "1000m"
          livenessProbe:
            httpGet:
              path: /actuator/health/liveness
              port: 8080
            initialDelaySeconds: 30
            periodSeconds: 10
            failureThreshold: 3
          readinessProbe:
            httpGet:
              path: /actuator/health/readiness
              port: 8080
            initialDelaySeconds: 15
            periodSeconds: 5
          startupProbe:
            httpGet:
              path: /actuator/health/liveness
              port: 8080
            initialDelaySeconds: 10
            periodSeconds: 5
            failureThreshold: 12
          env:
            - name: JAVA_TOOL_OPTIONS
              value: "-XX:MaxRAMPercentage=75.0"
---
apiVersion: v1
kind: Service
metadata:
  name: spring-app
spec:
  selector:
    app: spring-app
  ports:
    - port: 80
      targetPort: 8080
  type: ClusterIP

// build.gradle.kts
plugins {
    id("com.google.cloud.tools.jib") version "3.4.4"
}

jib {
    from {
        image = "eclipse-temurin:21-jre-alpine"
    }
    to {
        image = "registry.example.com/spring-app"
        tags = setOf("latest", project.version.toString())
    }
    container {
        jvmFlags = listOf(
            "-XX:MaxRAMPercentage=75.0",
            "-XX:+UseG1GC"
        )
        ports = listOf("8080")
        user = "1000"
    }
}

./gradlew jibDockerBuild    # Lokales Docker-Image
./gradlew jib               # Direkt in Registry pushen