CAP on SapMachine on Garden Linux Demo

Demo goal

Highligh thow easy it is to run JAVA apps based on SAP stack

• SAP Cloud Application Programming Model (CAP) is a framework of languages, libraries, and tools for building enterprise-grade services and applications. (from https://cap.cloud.sap/docs/about/)
• SapMachine is a free, open-source, non-commercial, cross-platform, and fully-functional production-grade version of the Open Java Development Kit (OpenJDK). Built and supported by SAP, it provides a robust and reliable Java environment. (from https://sap.github.io/SapMachine/)
• Garden Linux Container base image is a slim base image maintained by SAP Garden Linux team and well integrated with SapMachine for Java use-cases.
• Garden Linux OS as container runtime worker node orchestrated by Gardener

Demo Steps

1. Bootstrap locally a cap project
2. Package the app in SapMachine on Garden Linux container and demo that it works locally
3. Publish the container to a public image registry
4. Schedule the new app in a Gardener managed Kubernetes Cluster runing Garden Linux worker node (why not on Iron Core?)
5. Show the app works with kubectl port-forward

Demo execution flow

Local dev setup (before the demo)

Uses https://cap.cloud.sap/docs/java/getting-started

Expected state is that the cap prerequisites for Java local development are met and tooling is available

cds --version
java --version
mvn --version

Demo init (app init)

cds init demoapp --add java
mvn com.sap.cds:cds-maven-plugin:add -Dfeature=TINY_SAMPLE

Demo run (app local run)

mvn spring-boot:run
curl http://localhost:8080/odata/v4/CatalogService/

Package (app build)

mvn clean package spring-boot:repackage
mvn package spring-boot:repackage
java -jar ./srv/target/demoapp.jar
curl http://localhost:8080
curl http://localhost:8080/odata/v4/CatalogService/Books | jq

Build optimized JRE (jlink)

# For convenience, cd into the build directory
cd srv/target
# Unpack the jar so we can analyze the Java modules needed by our app's dependencies
jar xf demoapp.jar
# Identify the Java modules needed by our app and it's dependencies
jdeps --ignore-missing-deps -q --recursive --multi-release 21 --print-module-deps --class-path 'BOOT-INF/lib/*' demoapp.jar > deps.info
# Build an optimized version of the SAPMachine JRE with just the dependencies our app needs
jlink --add-modules $(cat deps.info) --strip-debug --no-header-files --no-man-pages --output ./tinysapmachine
# Show that our smaller JRE can run our app
./tinysapmachine/bin/java -jar demoapp.jar

With this we slimmed down the ~150 MiB JRE to about ~86 MiB (values might be different on your system, depending on your operating system and which dependencies your application has).

Publishing the app

podman build -t gcr.io/demoapp .
podman run --rm -ti -p 8080:8080 gcr.io/demoapp 
podman push gcr.io/demoapp

Scheduling the app

gardenctl ...
kubectl run gcr.io/demoapp
kubectl port-forward demoapp
curl http://localhost:8080
curl http://localhost:8080/odata/v4/CatalogService/Books | jq