Avoid double bundle install when using docker - ruby-on-rails

Question

I'm using docker as my dev environment for my rails app with the following docker-compose.yml :
app:
build: .
ports:
- "3000:3000"
links:
- db
- mail
volumes:
- .:/usr/src/app
- gemrc:/etc/gemrc
db:
image: mdillon/postgis
ports:
- "5432:5432"
environment:
- POSTGRES_USER=user
- POSTGRES_PASSWORD=password
- POSTGRES_DB=database
volumes:
- ./docker/pgdata:/var/lib/postgresql/data
mail:
image: djfarrelly/maildev
ports:
- "1080:80"
And my Dockerfile :
FROM rails:onbuild
When I need to add a new gem to my Gemfile, I have to first generate my Gemfile.lock :
docker run --rm -v gemrc:/etc/gemrc -v /home/user/project:/usr/src/app -w /usr/src/app ruby bundle install
And the rebuild the docker image:
docker-compose build
docker-compose up
Because of this I have to run bundle install twice without being able to add the --without development test flag. In order to do it quicker I added this to my gemrc file:
gem: --no-document
But is there a way to avoid the double bundle install ?

Answer 1

Perhaps you might want to try the following docker-compose workflow for development environment.
Similar to database.yml our docker-compose.yml is not included in our CVS (git), providing the similar benefits for developer custom config.
Build your image locally before starting your app container and tag it something like foo_app:latest. It makes sense because you're in dev. Just execute docker build . in your app's root directory, assuming your Dockefile is in that directory.
Define a data volume container for bundle and mount it in your app container. Your docker-compose.yml might look something like:
app:
image: foo_app
ports:
- "3000:3000"
links:
- db
- mail
volumes:
- .:/usr/src/app
volumes_from:
- bundle
bundle:
image: foo_app:latest
volumes:
- /home/app/bundle
db:
image: mdillon/postgis
ports:
- "5432:5432"
environment:
- POSTGRES_USER=user
- POSTGRES_PASSWORD=password
- POSTGRES_DB=database
volumes:
- ./docker/pgdata:/var/lib/postgresql/data
mail:
image: djfarrelly/maildev
ports:
- "1080:80"
Every time you need to add a new gem, just add it to your Gemfile and execute bundle install inside your app container. For example if your app container's name is foo_app_1:
docker exec foo_app_1 bundle install
The data volume container will always have the latest/edge snapshot of your app's gems.
Tag your releases and build the "official release image" in a central repository accessible for your staging/production/team.
With this approach every time you start/recreate your app container, all of your gems be just as they were the last time you updated them. You can also use this approach for other kind of data you want to be persisted across containers life cycles, adding "components" to manage state in your stateless applications.
See https://docs.docker.com/engine/userguide/containers/dockervolumes/ for more information