[peterwwillis]

With multi-stage builds you get a bunch of benefits. You can pull the heavy SDK when you start building the app, and that gets cached. Then when you package the image, you copy the jar that was built, but not the heavy SDK. When you run this again, the heavy/expensive steps are skipped because they're cached. Now you have a single set of operations to build your app and its production image, so there are no chances for inconsistencies.

In addition, you can build a separate container from a specific part of your multi-stage build (for example, if you want to build more apps based on the SDK step, or run tests which require debugging). So from one Dockerfile you can have multiple images or tags to use for different parts of your pipeline. The resulting production image is still based on the same origin code, so you have more confidence that what's going to production was what was tested in the pipeline.

Furthermore, devs can iterate on this Dockerfile locally, rather than trying to replicate the CI pipeline in an ad-hoc way. The more of your pipeline you stuff into a Dockerfile, the less you have to focus on "building your pipeline".