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Assignment 3 - Running Rails

For this and the remaining assignments, we will work with the demo application that is part of this repository. Make sure to change into the directory that you cloned this repository into (see here).

The Dockerfile

Just as before, we will create a Dockerfile inside the demo applications directory:

FROM jfahrer/ruby-on-ice:2.5.3-alpine

RUN apk add --update --no-cache \
      bash \
      build-base \
      nodejs \
      sqlite-dev \
      tzdata \
      postgresql-dev

RUN gem update bundler

WORKDIR /usr/src/app

COPY . .

RUN bundle install

CMD ["rails", "console"]

For convenience, I already put a .dockerignore file in place. Similar to a .gitignore file, the files and directories listed in the .dockerignore file will be ignored when copying data into the container image.

So, let's go ahead and build the image:

docker image build -t your_docker_id/rails_app:v1 .

Once the command completed successfully, we should be able to start a rails console in a container:

docker container run -it your_docker_id/rails_app:v1

Feel free to play around with the Rails environment for a bit. You should for example be able to create some records in the database:

Book.create!(title: "Rails With Docker", pages: 312)

The data is currently stored in SQLite database that is part of this repository and hence part of the container image as well.

Press Ctrl-D to quit the rails console and terminate the container.

Running the tests

As we've seen before, we can run arbitrary commands in the context of the container image by appending the command after the image name. We can use this technique to execute the test suite using rspec:

docker container run -it your_docker_id/rails_app:v1 rspec

Side note: We don't need the -it flags here because we don't run an interactive program like the Rails console. However, we will only see the colors in the output with the -t flag.

Finding out what is going on

The Docker CLI is pretty straight forward. To get more information about what is possible, try just typing docker. You will see a list of Commands and Management Commands. To get more information about a command, just append --help. For example

docker container run --help

Here are a few useful commands that you should try out before moving on to the next exercise.

docker container ls  # List all running containers
docker container ls -a  # List all containers - running or not
docker container rm <id/name> # Delete a container. Use the `-f` flag to delete a running container
docker container stop # Stop a running container
docker container kill # Kill a running container

Go ahead an try them out!

Cleaning up

After you are done, it is time to clean up a little bit. If you never used Docker before or don't care about any of the containers on your system, you can run:

docker container prune

!!Attention!! This will delete all stopped containers on your system.

If you care about any of the containers on your system, delete just the ones you don't need using docker container ls -a and docker container rm.

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