Rebuilding the image every time we make changes is tedious and slows us down in our development workflow. But Docker wouldn't be Docker if we couldn't work around this problem. The solution here are so called bind-mounts. A bind mount allows us to mount a local file or directory into the containers file system. When using the Docker CLI, you can specify the bind-mount using the -v flag. With Docker Compose, we simply add the definition the docker-compose.yml via the volumes directive. The resulting service definition will look like this:
app:
image: your_docker_id/rails_app:v1
build:
context: .
command: ["rails", "server", "--pid=/tmp/server.pid"]
environment:
- POSTGRES_HOST=pg
- POSTGRES_USER=postgres
- POSTGRES_PASSWORD=secret
- RAILS_ENV
volumes:
- ./:/usr/src/app
ports:
- 3000:3000
Please also note the --pid=/tmp/server.pid argument that we appended to rails server. This makes sure that we don't share the pidfile between multiple containers by storing it outside of the project directory (and bind mount).
Check out _examples/docker-compose.yml.with_bind_mount for a complete example. We can restart our containers with
docker-compose up -d
Docker Compose will pick up our changes and re-create the container for our app service. Make sure that everything is running with docker-compose ps and use docker-compose logs to troubleshoot any issues.
With the bind-mount in place, we can start iterating on our application. Here are a few things you can try:
- Fix the failing spec in the
ProgressUpdateJob(spec/jobs/progress_update_job_spec.rb) - Change some of the text in
app/views/books/ - Create a new model using the Rails generators
- Change one of the validations on books