Dockerizing Spring Boot Applications

Docker packages your Spring Boot app with its dependencies into a portable container that runs anywhere.

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Multi-Stage Dockerfile

# Stage 1: Build
FROM eclipse-temurin:21-jdk AS builder
WORKDIR /app
COPY pom.xml mvnw ./
COPY .mvn .mvn
RUN ./mvnw dependency:resolve
COPY src src
RUN ./mvnw package -DskipTests

# Stage 2: Run
FROM eclipse-temurin:21-jre
WORKDIR /app
COPY --from=builder /app/target/*.jar app.jar

# Non-root user
RUN groupadd -r appuser && useradd -r -g appuser appuser
USER appuser

EXPOSE 8080
ENTRYPOINT ["java", "-jar", "app.jar"]

docker build -t bookstore-api .
docker run -p 8080:8080 bookstore-api

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Docker Compose — Full Stack

services:
  app:
    build: .
    ports:
      - "8080:8080"
    environment:
      SPRING_PROFILES_ACTIVE: prod
      SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/bookstore
      SPRING_DATASOURCE_USERNAME: admin
      SPRING_DATASOURCE_PASSWORD: secret
      SPRING_DATA_REDIS_HOST: redis
    depends_on:
      postgres:
        condition: service_healthy
      redis:
        condition: service_started

  postgres:
    image: postgres:16
    environment:
      POSTGRES_DB: bookstore
      POSTGRES_USER: admin
      POSTGRES_PASSWORD: secret
    ports:
      - "5432:5432"
    volumes:
      - pgdata:/var/lib/postgresql/data
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U admin -d bookstore"]
      interval: 5s
      timeout: 5s
      retries: 5

  redis:
    image: redis:7
    ports:
      - "6379:6379"

volumes:
  pgdata:

docker compose up -d
docker compose logs -f app

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Spring Boot Docker Support (Buildpacks)

Spring Boot can build optimized images without a Dockerfile:

./mvnw spring-boot:build-image -Dspring-boot.build-image.imageName=bookstore-api

Uses Cloud Native Buildpacks — creates layered, optimized images automatically.

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Jib — Build Without Docker

<plugin>
    <groupId>com.google.cloud.tools</groupId>
    <artifactId>jib-maven-plugin</artifactId>
    <version>3.4.1</version>
    <configuration>
        <to>
            <image>registry.example.com/bookstore-api</image>
        </to>
    </configuration>
</plugin>

./mvnw jib:dockerBuild       # build to local Docker
./mvnw jib:build              # push to registry (no Docker needed)

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Image Optimization Tips

Tip	Impact
Use eclipse-temurin:21-jre (not JDK)	~200MB smaller
Multi-stage build	Build tools not in final image
Layer dependencies separately	Docker cache reuse
Non-root user	Security best practice
.dockerignore	Exclude target/, .git/, etc.

.dockerignore:

target/
.git/
.idea/
*.iml
.env

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Key Takeaways

1. Multi-stage builds — build with JDK, run with JRE.
2. Docker Compose for full-stack local development (app + DB + Redis).
3. Spring Boot Buildpacks create optimized images without Dockerfiles.
4. Jib builds images without Docker installed.
5. Always run as a non-root user in production containers.

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What’s Next?

Next: Async Processing — @Async, CompletableFuture, and non-blocking operations.