Docker: Use sockets for communication between 2 containers

Question

I have 2 Docker containers: App & Web.

App — simple container with php application code. It is used only for storage and deliver the code to the remote Docker host.

App image Dockerfile:

FROM debian:jessie
COPY . /var/www/app/
VOLUME ["/var/www/app"]
CMD ["true"]

Web — web service container, consist of PHP-FPM + Nginx.

Web image Dockerfile:

FROM nginx

# Remove default nginx configs.
RUN rm -f /etc/nginx/conf.d/*

# Install packages
RUN apt-get update && apt-get install -my \
  supervisor \
  curl \
  wget \
  php5-cli \
  php5-curl \
  php5-fpm \
  php5-gd \
  php5-memcached \
  php5-mysql \
  php5-mcrypt \
  php5-sqlite \
  php5-xdebug \
  php-apc

# Ensure that PHP5 FPM is run as root.
RUN sed -i "s/user = www-data/user = root/" /etc/php5/fpm/pool.d/www.conf
RUN sed -i "s/group = www-data/group = root/" /etc/php5/fpm/pool.d/www.conf

# Pass all docker environment
RUN sed -i '/^;clear_env = no/s/^;//' /etc/php5/fpm/pool.d/www.conf

# Add configuration files
COPY config/nginx.conf          /etc/nginx/
COPY config/default.vhost        /etc/nginx/conf.d
COPY config/supervisord.conf    /etc/supervisor/conf.d/
COPY config/php.ini             /etc/php5/fpm/conf.d/40-custom.ini

VOLUME ["/var/www", "/var/log"]

EXPOSE 80 443 9000

ENTRYPOINT ["/usr/bin/supervisord"]

My question: Is it possible to link Web container and App container by the socket?

The main reason for this - using App container for deploy updated code to remote Docker host. Using volumes/named volumes for share code between containers is not a good idea. But Sockets can help.

Thank you very much for your help and support!

Answer 1

If both containers run on the same host, it's possible to share a socket between the two as they are plain files.

You can create a local docker volume and mount that volume on both containers. Then configure you program(s) to use that path.

docker volume create --name=phpfpm
docker run phpfpm:/var/phpfpm web
docker run phpfpm:/var/phpfpm app

If the socket can be generated on the host you can mount the file into both containers. This is the method used to get a docker container to control the hosts docker.

docker run -v /var/container/some.sock:/var/run/some.sock web
docker run -v /var/container/some.sock:/var/run/some.sock app