How to share Docker Volume between two docker containers? - docker

Question

I have the following Problem: I have two Docker containers, one for my App and one for NGINX. Now I want to share uploaded images from my app with the NGINX container. I tried to do that using a volume. But when I restart my app container, the images are lost. What can I do to save the images, even after I restarted or recreated the container?
My configuration:
docker-compose.yml
version: '3'
services:
# the application
app:
build:
context: .
dockerfile: ./docker/app/Dockerfile
environment:
- DB_USERNAME=postgres
- DB_PASSWORD=postgres
- DB_PORT=5432
volumes:
- .:/app
- gallery:/app/public/gallery
ports:
- 3000:3000
depends_on:
- db
# the database
db:
image: postgres:11.5
volumes:
- postgres_data:/var/lib/postgresql/data
# the nginx server
web:
build:
context: .
dockerfile: ./docker/web/Dockerfile
volumes:
- gallery:/app/public/gallery
depends_on:
- app
ports:
- 80:80
networks:
default:
external:
name: app-network
volumes:
gallery:
postgres_data:
app/Dockerfile:
FROM ruby:2.7.3
RUN apt-get update -qq
RUN apt-get install -y make autoconf libtool make gcc perl gettext gperf && git clone https://github.com/FreeTDS/freetds.git && cd freetds && sh ./autogen.sh && make && make install
# for imagemagick
RUN apt-get install imagemagick
# for postgres
RUN apt-get install -y libpq-dev
# for nokogiri
RUN apt-get install -y libxml2-dev libxslt1-dev
# for a JS runtime
RUN apt-get install -y nodejs
# Setting an Envioronment-Variable for the Rails App
ENV RAILS_ROOT /var/www/app
RUN mkdir -p $RAILS_ROOT
# Setting the working directory
WORKDIR $RAILS_ROOT
# Setting up the Environment
ENV RAILS_ENV='production'
ENV RACK_ENV='production'
# Adding the Gems
COPY Gemfile Gemfile
COPY Gemfile.lock Gemfile.lock
RUN bundle install --jobs 20 --retry 5 --without development test
# Adding all Project files
COPY . .
RUN bundle exec rake assets:clobber
RUN bundle exec rake assets:precompile
EXPOSE 3000
CMD ["bundle", "exec", "puma", "-p", "3000"]
web/Dockerfile:
# Base Image
FROM nginx
# Dependiencies
RUN apt-get update -qq && apt-get -y install apache2-utils
# Establish where Nginx should look for files
ENV RAILS_ROOT /var/www/app
# Working Directory
WORKDIR $RAILS_ROOT
# Creating the Log-Directory
RUN mkdir log
# Copy static assets
COPY public public/
# Copy the NGINX Config-Template
COPY docker/web/nginx.conf /tmp/docker.nginx
# substitute variable references in the Nginx config template for real values from the environment
# put the final config in its place
RUN envsubst '$RAILS_ROOT' < /tmp/docker.nginx > /etc/nginx/conf.d/default.conf
EXPOSE 80
CMD ["nginx", "-g", "daemon off;"]

Answer 1

Rather than a volume, you can mount the same directory on the host to multiple Docker containers simultaneously. So long as the containers are not writing to the same file simultaneously, which is not in your described use case, you shouldn’t have a problem.
For example:
docker run -d --name Web1 -v /home/ubuntu/images:/var/www/images httpd
docker run -d --name Other1 -v /home/ubuntu/images:/etc/app/images my-docker-image:latest
If you would rather a Docker volume, this article will give you everything you need to know.