Use COPY instead of ADD for files and folders

[avelino]

Problematic code:

ADD ./cmd/prestd/prest.toml /app/prest.toml
ADD ./etc/entrypoint.sh /app/entrtpoint.sh

Correct code:

COPY ./cmd/prestd/prest.toml /app/prest.toml
COPY ./etc/entrypoint.sh /app/entrtpoint.sh

here: https://github.com/prest/prest/blob/d9d3ebc0d554e6fa8250630524c289303781bd90/Dockerfile#L11:L12

Rationale:

https://docs.docker.com/develop/develop-images/dockerfile_best-practices/#add-or-copy

For other items (files, directories) that do not require ADD’s tar auto-extraction capability, you should always use COPY.

Rule also implemented in https://github.com/RedCoolBeans/dockerlint/blob/master/src/checks.coffee

Exceptions:

Consequently, the best use for ADD is local tar file auto-extraction into the image.