Running JVM in Docker
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This document discusses running Java applications in Docker containers. It begins with a minimal example of dockerizing a Java HTTP server application and shows that the default Docker image is quite large at 726 MB. Alternative base images and techniques are explored to significantly reduce the image size, such as using Alpine Linux, Java 9+ modules, and building a native Java runtime. Memory limits are also discussed, noting that the default Docker memory settings are not optimal and cgroups values or Java ergonomics should be used instead. With these techniques, the example application's Docker image size was reduced to as small as 35 MB.
![A minimal Dockerfile
[ Demo ]](https://image.slidesharecdn.com/runningjvmindocker-181022151055/85/Running-JVM-in-Docker-4-320.jpg)
![A problem
● The JAR file size is 3.6 KB
● The Docker image size is 726 MB
● Is it something weird?
Why should I care about it?
● Larger image - slower deployment
● More unused stuff - more room for exploits
● Technical excellence
[ Demo ]](https://image.slidesharecdn.com/runningjvmindocker-181022151055/85/Running-JVM-in-Docker-5-320.jpg)
![Project Jigsaw
● Module system for Java
● Available starting from Java9
● Allows to build native JRE
Special thanks to Mikko Värri - https://github.com/vmj/http-server
[ Demo ]](https://image.slidesharecdn.com/runningjvmindocker-181022151055/85/Running-JVM-in-Docker-7-320.jpg)
![Dealing with memory limits
[ Demo ]](https://image.slidesharecdn.com/runningjvmindocker-181022151055/85/Running-JVM-in-Docker-10-320.jpg)
Running JVM in Docker
- 1. Running JVM in Docker Just scratching the surface © 2018 Zalando SE / Uri Savelchev This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License
- 2. Agenda 1. The quick way to dockerize your Java app 2. Reduce the container image footprint ○ Alternative base images ○ Jigsaw and native JRE 3. Setting memory limits ○ Out of the box default is wrong ○ Using cgroups and new JVM features ○ JVM ergonomics
- 3. A minimal HTTP server in Java
- 4. A minimal Dockerfile [ Demo ]
- 5. A problem ● The JAR file size is 3.6 KB ● The Docker image size is 726 MB ● Is it something weird? Why should I care about it? ● Larger image - slower deployment ● More unused stuff - more room for exploits ● Technical excellence [ Demo ]
- 6. So far we have shrunk the image by factor “9”! Docker image Local tag Size OpenJDK8 + Debian Stretch default 726 MB OpenJRE8 + Debian Strech “Slim” slim 205 MB OpenJRE8-musl + Alpine ultraslim 82 MB Can we do better?
- 7. Project Jigsaw ● Module system for Java ● Available starting from Java9 ● Allows to build native JRE Special thanks to Mikko Värri - https://github.com/vmj/http-server [ Demo ]
- 8. Got image smaller by factor 20 Docker image Local tag Size OpenJDK8 + Debian Stretch default 726 MB OpenJRE8 + Debian Strech “Slim” slim 205 MB OpenJRE8-musl + Alpine ultraslim 82 MB Jigsaw + OpenJRE11-musl + Alpine modular 35 MB Jigsaw + OpenJRE11-musl + Alpine - add Jolokia modular-jolokia 41 MB
- 9. Conclusions 1. Using Alpine allows to get images lesser than hundred megs 2. Jigsaw and modularization allows to make it even smaller, but a. You have to use Java9+ b. You have to build the native JRE inside Docker c. It’s more complex and therefore more fragile
- 10. Dealing with memory limits [ Demo ]
- 11. Conclusions 1. Don’t rely upon the default memory settings in Docker! 2. Use cgroups-provided value instead of environment variable 3. The default ergonomics is not good for Docker a. Either compute the memory limit yourself b. Or use -XX:MaxRAMPercentage=N for Java10+
- 12. References ● Materials for Helsinki Java meetup talk ● A Java HTTP server in 35MB Docker image ● Java inside Docker: What you must know to not FAIL Email: uri.savelchev@zalando.fi GitHub: https://github.com/alterrebe
- 13. Q&A