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18.1 Dockerizing a Spring Boot Application

1. Writing a Dockerfile (Multi-Stage Build)​

Multi-stage builds exclude build tools (Gradle, JDK) from the final image, keeping only the minimal JRE and JAR needed to run — dramatically reducing image size.

# ─── Stage 1: Build ───
FROM gradle:8.6-jdk21 AS builder
WORKDIR /app
COPY . .
RUN gradle bootJar --no-daemon

# ─── Stage 2: Runtime (final image) ───
FROM eclipse-temurin:21-jre-jammy
WORKDIR /app

# Security: run as non-root user
RUN addgroup --system spring && adduser --system --ingroup spring spring
USER spring:spring

COPY --from=builder /app/build/libs/*-SNAPSHOT.jar app.jar

ENV TZ=Asia/Seoul
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "app.jar"]

2. Docker Compose — Unified Local Development Environment​

services:
  app:
    build: .
    ports:
      - "8080:8080"
    environment:
      - SPRING_DATASOURCE_URL=jdbc:mysql://db:3306/tododb
      - SPRING_DATASOURCE_USERNAME=root
      - SPRING_DATASOURCE_PASSWORD=secret
      - SPRING_DATA_REDIS_HOST=redis
    depends_on:
      db:
        condition: service_healthy
      redis:
        condition: service_started

  db:
    image: mysql:8.0
    environment:
      MYSQL_ROOT_PASSWORD: secret
      MYSQL_DATABASE: tododb
    ports:
      - "3306:3306"
    healthcheck:
      test: ["CMD", "mysqladmin", "ping", "-h", "localhost"]
      interval: 10s
      retries: 5

  redis:
    image: redis:7.0
    ports:
      - "6379:6379"

A single docker compose up --build gives you a complete dev environment with the app, MySQL, and Redis running together.

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