Why is the Docker Image Size for OpenJDK 11 (openjdk:11-jre-slim) Larger Than That of OpenJDK 8?

What factors contribute to the larger size of the Java 11 base Docker image (openjdk:11-jre-slim) compared to Java 8 (openjdk:8-jre-alpine)?

The size discrepancy between the OpenJDK 11 Docker image and its predecessor OpenJDK 8 can be attributed to various factors, including base image selections, package size differences, and structural changes in the JDK.

...1. Dockerfile Example  
   
   FROM openjdk:11-jre-slim  
   COPY target/my-app.jar app.jar  
   ENTRYPOINT ["java","-jar","/app.jar"]  
   
   # Use multi-stage builds for size optimization  
   FROM openjdk:11-jre-slim AS build  
   COPY . /src  
   RUN javac /src/MyApp.java  
...

Causes

• The openjdk:11-jre-slim image is based on debian:sid-slim, which is inherently larger than alpine:3.8 used for Java 8.
• Debian sid is an unstable version, potentially increasing the image size and complexity.
• The size of the openjdk-11-jre-headless package is approximately three times larger than that of openjdk-8-jre.
• The introduction of the 'modules' system in JDK 11 significantly increases the size due to the larger lib directory.

Solutions

• Consider using the openjdk:11-jre-alpine image if minimal size is a priority, though it may come with compatibility trade-offs.
• Look into optimizing Docker images using multi-stage builds to strip unnecessary layers and reduce the final image size.
• Evaluate whether your application can utilize a different base image that better fits your size requirements.

Mistake: Using the wrong base image for a Java application without considering size and stability.

Solution: Carefully evaluate the base image based on the application requirements and deployment environment.

Mistake: Not utilizing multi-stage builds to reduce Docker image size.

Solution: Incorporate multi-stage Docker builds to create leaner images by separating build dependencies from runtime.