Depends on the nature of the build artefacts? Gems, jars and NPM packages get posted to a jFrog artefactory. Go and Cocoapods just use straight Git, so Jenkins actually makes commits for those (and in the case of Go, version tags) from inside the Docker container. For the EMR clusters, there's a step in the build script that uploads the files to S3.
Another way to do it would be to have the `docker run` / `docker build` script be given a mounted volume that maps to the system's, and then it would write the blobs to that volume, where (I think?) they'd then be accessible to the outer system.
Another way to do it would be to have the `docker run` / `docker build` script be given a mounted volume that maps to the system's, and then it would write the blobs to that volume, where (I think?) they'd then be accessible to the outer system.