The advantage that Docker brings isn't perfect guaranteed reusability, it's complete independence (or as close you can easily get while not wasting resources on

The advantage that Docker brings isn't perfect guaranteed reusability, it's complete independence (or as close you can easily get while not wasting resources on VMs) from the system on which the build is running, plus some resuability in practice in a certain period of time, and given other good practices. Sure, if I try to rebuild a docker image from 5 years ago, it may fail, or produce something different, because it was pulling in some packages that have changed significantly in apt, or perhaps pip has changed encryption and no longer accepts TLS1.1 or whatever. And if you use ':latest' or if your team has a habit of reusing build numbers or custom tags, you may break the assumptions even sooner. But even so, especially if using always incremented build numbers as image tags, a docker image will work the same way om the Jenkins system, the GitHub Actions pipeline, and every coworker's local build, for a while.