The Dockerfile is a simple update to use the golden image in the final stage:
courselabs/java:jre-21.12 for the runtimeThe POM should be updated so that Micrometer uses an explicit version instead of a range, and the JAR plugin uses the latest:
You can build the sample solution with a new tag:
docker build -t app-3:v2 ./labs/golden-images/lab/
Check the app images:
docker image ls app-3
On my system the v2 image is about 30% smaller:
REPOSITORY TAG IMAGE ID CREATED SIZE
app-3 v1 90f85a6e8be0 2 minutes ago 221MB
app-3 v2 cbc2c31a0685 2 minutes ago 184MB
And if you inspect the images to see the layers:
docker inspect app-3:v1
docker inspect app-3:v2
You'll see v1 has a different set of layers - no commonality with any of the other Java apps we've built. v2 shares the same base layers as the v2 images from app-1 and app-2, so we're maximizing the layer cache as well as enforcing an approved base image.
Back to the exercises.