Let's reiterate: Docker is a virtual machine with an OS that is capable of managing containers. So, how to bring the container image to a required tools, libs and settings? Via an instruction file, of course, because this process has to be reproducible on a dev machine, in staging, in production, and anywhere else.
A Dockerfile is a set of instructions that take a source image and bring it to a desired state, which results in an image too. Any existing Dockerfile's outcome image could in turn be taken as a source for another one, and so on.
Let's start with a super-minimal set of packages:
$ npm i react react-dom isomorphic-unfetch --save
$ npm i next --save-dev
Next, we create scripts in package.json as usual:
"build": "next build",