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Comment by rossmohax | Hacker News Reader

in Docker that would be something like

  COPY Gemfile Gemfile.lock /src
  RUN bundle install

even if they don't use docker to run application in prod, it can be [ab]used to perform efficient build layer (build step) caching and distribution.

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That's what a mistry recipe looks like, with some additional conventions (e.g. params are accessible in the project as files located in `/data/params`). mistry recipes are essentially Dockerfiles.

Problem with docker is there if something early on changes then everything after needs to be rebuild.

However with a build you might have A and B feed into C. If A changes and B hasn't you want to just build A and get B from cache.

One solution in Docker is multistage builds where A and B can be separated into intermediate images with results copied into C.

A pattern that I like to use is two multistage build Dockerfiles- `dev` and `prod`.

The `dev` image has 2 stages. The first stage copies only files required by the package manager, such as `package.json` into another directory using a combination of `find` and `cp --parents`, then restores dependencies. The second stage copies the dependencies from the first stage and overlays source code. The `dev` image is then instantiated to run all tests.

The `prod` image also has 2 stages. The first stage starts with the `dev` image and publishes a production bundle to a directory. The second stage starts with a clean image and copies the production bundle from the first stage.

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