Docker promised containers like we knew them from the past, and improved building and packaging procedures. In the past, we never had an easy way to package va

Docker promised containers like we knew them from the past, and improved building and packaging procedures. In the past, we never had an easy way to package various applications (including all needed resources and executables). Each language ecosystem invented their own ways of packaging, distributing and installing the application, and this always relied on pre-existing environment. With Docker you don't care what versions of language runtime, or dependencies, each application runs, you can run them on the same machine. There are no incompatible dependencies between multiple Docker containers, everything almost always works. Same goes with building, image layers made building of images a lot easier, and doing incremental changes is fast. Of course there are downsides, image size can really grow if you are not careful, and you need to regularly rebuild images from the ground up, to ensure everything is patched.