Docker 卷未安装在容器中

Question

I'm trying to mount a volume using docker-compose so I can hot reload some C code when developing. I've used Docker a couple times before and specifically hit this use case while working on a nodejs website but I'm completely at a loss here.

My docker-compose.yml and Dockerfile have been stripped down entirely to just the bare minimum. I would like to mount my current directory (all source code) into the container. My Dockerfile just installs some dependencies, sets the working directory and then attempts to run the makefile while my docker-compose.yml adds the volume. The result is a container that cannot access the mounted volume and resulting code (it's nothing wrong with the Makefile as it works on the host directory and when copied in, instead of using a volume). Does anyone see anything wrong with either of these files? It appears the /cfs folder isn't even being created in the container. I tried mounting it to the home directory to no avail.

docker-compose.yml

version: '3'

services:
  cfs:
    volumes:
      - ./:/cfs
    build:
        context: ./
        dockerfile: ./Dockerfile
    networks:
      - default
  
networks:
  default:
    internal: true    

Dockerfile

FROM ubuntu:20.04

# install dependencies
RUN apt-get -qy update                           \
    && apt-get -y install                        \
        cmake=3.16.3-1ubuntu1                    \
        make=4.2.1-1.2                           \
        gcc=4:9.3.0-1ubuntu2                     \
        g++=4:9.3.0-1ubuntu2

WORKDIR /cfs

RUN make prep
RUN make
RUN make install

Answer 1

Most Compose settings aren't visible during an image build. volumes: aren't mounted, environment: variables aren't set, networks: aren't accessible. Only the settings within the immediate build: block have an effect.

That means you should look at the Dockerfile in isolation, ignoring the docker-compose.yml file. At that point, the /cfs directory is empty (you don't COPY any source code into it), so the RUN make... commands will fail. It doesn't matter that the directory will eventually have something else mounted over it.

If you're just planning to recompile the application when the source code changes, delete the volumes: , COPY the source into the image, and run docker-compose build at the point you'd typically run make . If you do have a setup that can rebuild the application when its source changes, you need to set the image's CMD to launch that, but if you don't COPY the source in, you can't build it at image build time. (...and if you're going to overwrite the entire interesting content of the image with a volume, it will get lost anyways.)