Revised onbuild images

[tsloughter]

I was trying out multi-stage builds and wanted to create a generic onbuild image others could use to build their minimal release images.

I think this would be a more appropriate onbuild set of instructions that what current exists:

ONBUILD WORKDIR /usr/src/app
ONBUILD COPY . /usr/src/app
ONBUILD RUN rebar3 as prod tar

ONBUILD RUN mkdir -p /opt/rel
ONBUILD RUN tar -zxvf /usr/src/app/_build/prod/rel/*/*.tar.gz -C /opt/rel

The use of tar is important because of how Erlang target systems are built that changes around a few things from just the built release and use of the prod profile so the user can specify how they want their project built for production.

Then the user can make their Dockerfile (with docker 17.05 and above):

FROM erlang:19.3.3-onbuild as builder

FROM ubuntu:16.04

ENV RELX_REPLACE_OS_VARS true
<any ENV vars they want defaults set of>

WORKDIR /opt/<RELEASE NAME>
COPY --from=builder /opt/rel /opt/<RELEASE NAME>
ENTRYPOINT ["/opt/<RELEASE NAME>/bin/<RELEASE NAME>"]

What do you think?

[c0b]

are you aware of https://github.com/docker-library/docs/pull/911/files it seems many users want to customize ONBUILD process but it doesn't have the flexibility

+The ONBUILD image variants are deprecated, and their usage is discouraged. For more details, see docker-library/official-images#2076.

I was keeping 19/onbuild/ directory only for travis-ci, but after I redesigned .travis-ci.yaml process the onbuild/ directory is no longer needed;

For your showed case, I agree it could be a good one, from above docker-library# the recommended way is we may document it as a good minimal example of using multi-stage build, it's just like for end users to copy all ONBUILD instructions

FROM erlang:19 as builder
# copy all ONBUILD instructions here

FROM ubuntu:16    # or from alpine:3.6
COPY --from=builder /opt/rel ...

[tsloughter]

Oh, weird, I was not aware. Then yea, your suggestion of it as a documentation piece is good.