Step 7 — Deploy

If your code only runs on your laptop, it doesn't exist. Wrap it as a Docker image so it runs the same anywhere.

Dockerfile

FROM gradle:8.10-jdk21 AS builder
WORKDIR /app
COPY . .
RUN gradle bootJar --no-daemon

FROM eclipse-temurin:21-jre-alpine
WORKDIR /app
COPY --from=builder /app/build/libs/*.jar app.jar
EXPOSE 8080
ENTRYPOINT ["java", "-jar", "app.jar"]

bootJar is Spring's fat jar. Multi-stage shrinks the final image to ~1/3.

📌 Spring Boot 4 note: java -Djarmode=tools ... extract --layers for the four-layer split (dependencies/loader/snapshot/application) has a compatibility issue (verified in the warragon monorepo on 2026-05-14) — the standard directories come out empty and the actual content lands in a <artifact>-<version>/ directory, breaking the JarLauncher classpath. For now the safe path is a single COPY *.jar app.jar + ENTRYPOINT ["java", "-jar", "app.jar"]. Retry on Boot 5+.

docker-compose with DB

services:
  postgres:
    image: postgres:17-alpine
    environment:
      POSTGRES_DB: mydb
      POSTGRES_USER: user
      POSTGRES_PASSWORD: secret
    volumes: [pg-data:/var/lib/postgresql/data]
    healthcheck:
      test: ["CMD-SHELL", "pg_isready -U user"]
      interval: 5s

  app:
    build: .
    depends_on: { postgres: { condition: service_healthy } }
    environment:
      SPRING_DATASOURCE_URL: jdbc:postgresql://postgres:5432/mydb
      SPRING_DATASOURCE_USERNAME: user
      SPRING_DATASOURCE_PASSWORD: secret
    ports: ["8080:8080"]

volumes:
  pg-data:

docker compose up -d — DB and app together.

Pre-deploy checklist

• ✅ application-prod.yml separated
• ✅ actuator/health exposed
• ✅ Dockerfile HEALTHCHECK
• ✅ Caddy / Nginx for HTTPS
• ✅ Automated DB backups (cron or admin UI)

Caddy = HTTPS in one line

api.example.com {
    reverse_proxy app:8080
}

Caddy fetches Let's Encrypt certs automatically.

Try it

Add the Dockerfile + docker-compose.yml to your project, run docker compose up -d --build, and visit http://localhost:8080/api/posts.

Going deeper

• Docker basics
• docker-compose patterns
• Caddy

Next

Course complete. Try devops-cloud (cloud deployment) or python-data-pipeline (data flows).