Multi-stage Docker builds in Spring Boot - Mini Project: Build & Apply

Multi-stage Docker builds with Spring Boot

📖 Scenario: You are creating a Docker image for a Spring Boot application. To keep the image small and efficient, you will use a multi-stage Docker build. This means you first build the application in one stage, then copy only the necessary files to a smaller runtime image.

🎯 Goal: Build a multi-stage Dockerfile that compiles a Spring Boot app using Maven in the first stage, then copies the built jar to a smaller OpenJDK runtime image in the second stage.

📋 What You'll Learn

Use maven:3.9.0-eclipse-temurin-17 as the build stage base image

Run mvn clean package to build the Spring Boot jar

Use eclipse-temurin:17-jre as the runtime stage base image

Copy the jar from the build stage to the runtime stage

Set the ENTRYPOINT to run the jar with java -jar

💡 Why This Matters

🌍 Real World

Multi-stage Docker builds help create smaller, efficient container images by separating build and runtime environments. This is common in real-world Spring Boot deployments.

💼 Career

Understanding multi-stage Docker builds is essential for developers and DevOps engineers to optimize container images and improve deployment workflows.

1

Create the build stage

Write the first stage of the Dockerfile named build using the base image maven:3.9.0-eclipse-temurin-17. Set the working directory to /app. Copy the pom.xml and src folder into /app.

Spring Boot

FROM maven:3.9.0-eclipse-temurin-17 AS build
WORKDIR /app
# Copy pom.xml and src folder
# Your code here

Need a hint?

Use FROM to specify the base image and name the stage build. Use WORKDIR to set the directory. Use COPY to copy files.

2

Add the build command

In the build stage, add a command to run mvn clean package to build the Spring Boot jar.

Spring Boot

FROM maven:3.9.0-eclipse-temurin-17 AS build
WORKDIR /app
COPY pom.xml .
COPY src ./src
# Run Maven package command
# Your code here

Need a hint?

Use RUN to execute the Maven build command inside the container.

3

Create the runtime stage and copy the jar

Create a second stage named runtime using the base image eclipse-temurin:17-jre. Set the working directory to /app. Copy the built jar file target/demo-0.0.1-SNAPSHOT.jar from the build stage to /app/app.jar in the runtime stage.

Spring Boot

FROM maven:3.9.0-eclipse-temurin-17 AS build
WORKDIR /app
COPY pom.xml .
COPY src ./src
RUN mvn clean package

# Create runtime stage
# Your code here

Need a hint?

Use FROM to start the runtime stage. Use COPY --from=build to copy the jar from the build stage.

4

Set the entrypoint to run the jar

In the runtime stage, add an ENTRYPOINT instruction to run the jar file with java -jar /app/app.jar.

Spring Boot

FROM maven:3.9.0-eclipse-temurin-17 AS build
WORKDIR /app
COPY pom.xml .
COPY src ./src
RUN mvn clean package

FROM eclipse-temurin:17-jre AS runtime
WORKDIR /app
COPY --from=build /app/target/demo-0.0.1-SNAPSHOT.jar ./app.jar
# Add ENTRYPOINT to run the jar
# Your code here

Need a hint?

Use the JSON array syntax for ENTRYPOINT to run the jar file.