Chapter 20 · Azure Kubernetes App Deploy

Subchapter 20.8

Java

Python

Rust

Deploy

templates/k8s/11 files

12 more in the appendix

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templates/dockerfiles/java.Dockerfile

DOCKERFILE78 lines3 KB

1# =============================================================================
2# Java (Spring Boot / Maven) Production Dockerfile
3# =============================================================================
4# Customize the following before use:
5#   - JAR_FILE:    Adjust the glob pattern if your build output differs
6#   - PORT:        Change EXPOSE port if not 8080
7#   - JVM_OPTS:    Tune -Xmx, -Xms, GC flags, etc. via JAVA_OPTS env var
8#
9# Gradle users:
10#   Replace the Maven wrapper commands in the build stage with:
11#     COPY gradlew build.gradle.kts settings.gradle.kts ./
12#     COPY gradle ./gradle
13#     RUN ./gradlew dependencies --no-daemon
14#     COPY . .

java.Dockerfile on GitHub

# RUN ./gradlew bootJar --no-daemon

# And adjust the JAR_FILE path to "build/libs/*.jar"

# =============================================================================

# ---------------------------------------------------------------------------

# Stage 1: Build

# ---------------------------------------------------------------------------

# Base: current Java LTS (Temurin). See references/base-images.md for the Microsoft OpenJDK alternative.

FROM eclipse-temurin:<LATEST_STABLE_JAVA_JDK>-jdk-alpine AS build

WORKDIR /app

# Layer caching: copy Maven wrapper and POM first so dependency resolution is

# cached independently of source changes.

COPY mvnw pom.xml ./

COPY .mvn .mvn

# Download dependencies (offline-friendly layer)

RUN chmod +x mvnw \

&& ./mvnw dependency:go-offline -B

# Copy source and build the fat JAR

COPY src ./src

# -Dspring-boot.repackage.finalName=app ensures a single predictably named fat JAR,

# avoiding glob ambiguity when Maven produces both thin and fat JARs.

RUN ./mvnw package spring-boot:repackage -DskipTests -B \

-Dspring-boot.repackage.finalName=app \

&& mv target/app.jar app.jar

# ---------------------------------------------------------------------------

# Stage 2: Runtime

# ---------------------------------------------------------------------------

FROM eclipse-temurin:<LATEST_STABLE_JAVA_JRE>-jre-alpine

WORKDIR /app

# AKS Deployment Safeguards DS004: create and switch to a non-root user

RUN addgroup -S appuser && adduser -S appuser -G appuser

# Copy only the built JAR from the build stage

COPY --from=build --chown=appuser:appuser /app/app.jar ./app.jar

# Spring Boot Layered JARs: if using layered JARs, replace the COPY above

# with the extract + copy approach for even better layer caching:

# RUN java -Djarmode=layertools -jar app.jar extract

# COPY --from=build /app/dependencies/ ./

# COPY --from=build /app/spring-boot-loader/ ./

# COPY --from=build /app/snapshot-dependencies/ ./

# COPY --from=build /app/application/ ./

USER appuser

EXPOSE 8080

# MaxRAMPercentage caps heap relative to the container memory limit

# (container-aware by default in JDK 21).

ENV JAVA_OPTS="-XX:MaxRAMPercentage=75.0 -XX:+UseG1GC"

# No HEALTHCHECK: the JRE Alpine image does not include wget or curl.

# Kubernetes liveness/readiness probes (configured in deployment.yaml) handle

# health checking in AKS.

ENTRYPOINT ["sh", "-c", "exec java $JAVA_OPTS -jar app.jar"]