On 16/06/2015, at 10:16 AM, Eibriel Inv <[email protected]> wrote:
> Hi!
> I've noticed that every time I make a change on the code I need to rebuild
> the container and the build script install the pip requirements (which is
> time consuming).
>
> How can I install my own requirements from Dockerfile to prevent that?
Is the issue with this because you are trying to use the docker image during
development and so are making fast turn around changes?
The reason you are seeing what you are seeing is because the 'onbuild' docker
image is written as:
FROM grahamdumpleton/mod-wsgi-docker:python-2.7
WORKDIR /app
ONBUILD COPY . /app
ONBUILD RUN mod_wsgi-docker-build
EXPOSE 80
ENTRYPOINT [ "mod_wsgi-docker-start" ]
Because the requirements.txt file is a part of the directory that needs to be
copied into the docker image, then any change to the project directory will
result in the latter build phase being triggered. It is the build phase that
pip is run from to install the requirements.
This sort of arrangement is quite typical for Python docker images.
If you weren't using this image with the mod_wsgi-docker-build script and doing
things explicitly, you could probably get away with using something like:
WORKDIR /app
COPY requirements.txt /app/requirements.txt
RUN pip install -r requirements.txt
COPY . /app
With this, because the requirements.txt file is copied separately, so long as
that file along isn't changed, the pip wouldn't be run.
The whole point with mod_wsgi-docker-build though is that it does other stuff
before pip is run to properly set up the environment. This means it cannot be
split out in that way.
If the problem is because you are trying to use it for quick turnaround changes
in a development environment, there may be a better way, although I would have
to tweak how the images work.
What one other person did, perhaps due to also wanting to do things in a
development environment, was to copy my docker images and change them to have
the application directory mounted in as a volume.
They possibly weren't thinking of the pip install problem, but wanted to be
able to modify code on the fly, touch the WSGI script file and have the
mod_wsgi in the docker instance automatically reload it.
In other words, wouldn't be necessary to stop the container.
Rather than copy my docker images and change them, notionally you could achieve
the same thing by doing:
docker build -t myapp .
docker run -it -v `pwd`:/app myapp
That is, build the docker image once, which will result in all the packages
being installed, and then run it, with it using the live code from your host.
You would only need to do a rebuild if you change the requirements.txt file.
Unfortunately, as written this will not work.
The problem is that the docker images themselves stored various stuff inside of
the /app directory and what is in it isn't just your application code. Thus the
script to start everything up isn't found.
What I could do though is change the images such that the special stuff from
the base image isn't stored under /app where your application is placed, and
puts it somewhere else.
If I do that, then the mounting volume trick should work and allow for this
sort of behaviour.
So can you explain the scenario of where this is a problem so I can understand
better the needs you have and whether this change would work?
Thanks.
Graham
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