Use one dockerfile to build from two different sources - docker

Question

I want to create a docker image using either git sources, or the already build app. I created two Dockerfiles like these (note: this is pseudo code):
Runtime-Image:
FROM <baseimage>
EXPOSE 1234/tcp
EXPOSE 4321/tcp
VOLUME /foobar
COPY myapp.tgz .
RUN tar -xzf myapp.tgz && rm -f myapp.tgz
ENTRYPOINT ["myapp"]
myapp.tgz is created on a buildserver or maybe by compiling manually. It is available on the docker host server locally.
To build directly from source I use:
FROM <devimage> AS buildenv
ARG GIT_USER
ARG GIT_PASSWORD
RUN git clone http://${GIT_USER}:${GIT_PASSWORD}#<my.git.host>
RUN ./makefile && cp /source/build/myapp.tgz /drop/myapp.tgz
FROM <baseimage> AS runenv
EXPOSE 1234/tcp
EXPOSE 4321/tcp
VOLUME /foobar
COPY --from=buildenv /drop/myapp.tgz .
RUN tar -xzf myapp.tgz && rm -f myapp.tgz
ENTRYPOINT ["myapp"]
The instructions in the second build stage of this are obviously a duplicate of the Runtime-Image Dockerfile.
I'd like to have just ONE Dockerfile, which can build from source, or from context on the docker host, as required. I could put the duplicated commands in a custom baseimage and reuse that to build onto (FROM), but this would obfuscate the Dockerfile.
What is the recommended, most elegant way to do this?
I can't use a bind mount to get myapp.tgz in the current directory on the docker host, can I? For this I would have to start a Container to build my app?
There is no IF directive in the Dockfile for conditions?
If there is no myapp.tgz on the docker host, COPY myapp.tgz . will fail
If there is no buildenv, COPY --from=buildenv /drop/myapp.tgz . will fail.
I could use COPY ./* . and then check with
[ -f /myapp.tgz ] && <prepare-container> || <build-from-git-source>
I guess? Our would you rather just create a seperate Dockerfile just for building from source and then use something like
docker run --rm -v /SomewhereOnHost/drop:/drop my-compile-image

Answer 1

For the past 2 days I have been trying to figure this out, now I have a good solution to achieve a conditional build (a if in Dockerfile)
ARG mode=local
FROM alpine as build_local
ONBUILD COPY myapp.tgz .
FROM alpine as build_remote
ONBUILD RUN git clone GIT_URL
ONBUILD RUN cd repo && ./makefile && cp /source/build/myapp.tgz .
FROM build_${mode} AS runenv
EXPOSE 1234/tcp
EXPOSE 4321/tcp
VOLUME /foobar
RUN tar -xzf myapp.tgz && rm -f myapp.tgz
ENTRYPOINT ["myapp"]
The toplevel mode allows you to pass the condition with docker build --build-arg mode=remote .. ONBUILD is used so the command is only executed if the corresponding branch is selected.