Docker Volume overwriting file permissions - linux

Question

I have a Dockerfile where I bring in some files and change permissions.
I also have a docker-compose that creates a volume for nodemon to watch. I believe that these volumes are overwriting the permissions that I set. When I remove the volumes the app works but I don't get the server restarting. When the volumes are there the app crashes due to permissions. I've tried creating the volume first but perhaps I was doing that wrong.
FROM ubuntu:16.04
RUN apt-get update && apt-get install -y --no-install-recommends curl sudo
RUN curl -sL https://deb.nodesource.com/setup_9.x | sudo -E bash -
RUN apt-get install -y nodejs && \
apt-get install --yes build-essential
RUN apt-get install --yes npm
#VOLUME "/usr/local/app"
# Set up C++ dev env
RUN apt-get update && \
apt-get dist-upgrade -y && \
apt-get install gcc-multilib g++-multilib cmake wget -y && \
apt-get clean autoclean && \
apt-get autoremove -y
#wget -O /tmp/conan.deb -L https://github.com/conan-io/conan/releases/download/0.25.1/conan-ubuntu-64_0_25_1.deb && \
#dpkg -i /tmp/conan.deb
#ADD ./scripts/cmake-build.sh /build.sh
#RUN chmod +x /build.sh
#RUN /build.sh
RUN curl -sL https://deb.nodesource.com/setup_9.x | sudo -E bash -
RUN apt-get install -y nodejs sudo
RUN mkdir -p /usr/local/app
WORKDIR /usr/local/app
COPY package.json /usr/local/app
RUN ["npm", "install"]
RUN npm install --global nodemon
COPY . .
RUN echo "/usr/local/app/dm" > /etc/ld.so.conf.d/mythrift.conf
RUN echo "/usr/lib/x86_64-linux-gnu" >> /etc/ld.so.conf.d/mythrift.conf
RUN echo "/usr/local/lib64" >> /etc/ld.so.conf.d/mythrift.conf
RUN ldconfig
EXPOSE 9090
RUN ["chmod", "+x", "dm/dm3"]
RUN ["chmod", "777", "policy"]
RUN ls -al .
RUN npm -v
RUN node -v
notice at the end where i'm changing permissions.
version: '3'
services:
web:
build: .
volumes:
- .:/usr/local/app/
- /usr/app/node_modules
command: nodemon
ports:
- "3000:3000"

Answer 1

When you mount volumes into a docker container, the files inside are on a lower layer so they are hidden.
In your case, /usr/local/app from the Dockerfile is hidden. Its contents are the files from the host machine (the parent directory of docker-compose.yml). You should set the permissions in the host machine.