Alpine is an option in some cases, but, like you said, it's not always straight forward. Native application modules, 3rd party OS packages and the overall package echosystem differences are important factors that need to be considered. This is why DockerSlim [1] was created. You use a regular distro like Ubuntu and you still get micro containers! Note that the sample node microcontainer with DockerSlim is 14MB and in this post it's 29MB :-) It uses hapi.js instead of express.js though, but it's probably not the main reason for the size difference.

[1] http://dockersl.im