Say I have organization/db, which runs a Postgres instance, running and exposing port 5432; I also have organization/app running, which is linked to my database instance. If I want to upgrade my version of Postgres and restart the database, I also have to restart organization/app, since the database link will be broken when the database container is restarted.

It would be cool if we could docker replace a running container with a new container running a different image, which replaces the running container and usurps its port and virtual interface, so that the app won't even be able to tell its database was replaced, and the most downtime users would see would be one or two misc. network errors when trying to reach the database.