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Using custom JREs (Java Runtime Environment) tailored to specific applications, instead of using the full JDK (Java Development Kit) or a larger JRE, offers several advantages.
Here's why every team should consider creating their custom JRE:
Reduced Image Size:
One of the most immediate benefits is a significant reduction in the image size, especially when used with containerized applications. A smaller image means faster deployments, quicker scaling, and reduced storage costs.
A smaller image size is particularly beneficial in cloud environments where bandwidth, storage, and startup times are crucial.
Faster Start-up Time:
Security:
Minimizing the runtime surface can reduce the security risk. Fewer components in the JRE mean fewer potential vulnerabilities.
Regularly updating a custom JRE can be simpler, ensuring that you're always using the most secure version of the modules you need.
Optimized Resource Utilization:
Simplified Dependency Management:
Improved Portability:
Version Consistency:
Better Understanding of Dependencies:
Tailored to Needs:
However, while there are many benefits, there are also considerations:
Maintenance Overhead: Creating and maintaining custom JREs does introduce some overhead. Teams need to ensure they keep their custom JREs up to date with security patches and updates.
Testing: With a custom JRE, thorough testing is paramount. Teams must ensure they haven't omitted crucial modules or made changes that affect the application's functionality.
Java's jlink tool offers the creation of custom JREs tailored to specific applications. This process can substantially reduce the image size of Java applications.
This guide illustrates how to create a custom JRE for Java services, including Java EE applications deployed in JBoss and Spring Boot applications with embedded Tomcat server.
Java 9 or later.
A Spring Boot or Java EE application.
Docker (if building Docker images).
Tomcat, JBoss or any application server
Analyze Dependencies with jdeps: jdeps is a dependency analysis tool.
jdeps --print-module-deps path/to/your/app.jar
This will give a list of modules your application needs.
If you get a lot "not found" modules which are external modules, then run the jdeps command with --ignore-missing-deps flag. This should give you a clearer result.
Create the Custom JRE using jlink:
jlink --no-header-files
--no-man-pages
--compress=2
--strip-debug
--add-modules java.base,java.sql,java.logging,...
--output customjre
Integrate with Docker
For non-JBoss services:
```java FROM openjdk:17 as jre-builder WORKDIR /jre-builder RUN jlink --no-header-files \ --no-man-pages --compress=2 \ --strip-debug \ --add-modules java.base,java.sql,java.logging,... \ --output custom-jre
FROM debian:bullseye-slim WORKDIR /app
COPY --from=jre-builder /jre-builder/custom-jre /opt/custom-jre
COPY --from=build /app/target/your-app-name.jar /app.jar
EXPOSE 8080
ENTRYPOINT ["/opt/custom-jre/bin/java", "-jar", "/app.jar"] ```
Iterative Testing: Errors like ClassNotFoundException suggest missing dependencies. If they arise:
Identify the missing module.
Re-run the jlink command to include the additional module.
Test again.
Document the Process:
Test applications thoroughly after applying a custom JRE.
While storage is relatively cheap, reducing image size provides faster deployments and start-ups, especially in containerized environments.
Regularly update the base image and regenerate the custom JRE to keep up with security patches.
Using a custom JRE can optimize your Spring Boot and Java EE services for various deployment environments.
By reducing image sizes, you achieve faster deployments and better resource utilization. Always test thoroughly and keep the JRE updated.