- To successfully follow this guide you will first need to install Docker on your local machine.
- You will also need a Docker Hub account, which includes 1 free private repository.
- We will be using Docker Hub throughout this learn guide, but GitLab (including the self-hosted version) comes with a built-in container registry for unlimited repositories and is a great alternative.
Dockerfile in the root of your project.
# We're currently using Ruby 2.5.1 FROM ruby:2.5.1-alpine # Always nice to know who to contact LABEL maintainer="email@example.com" # In a single step - install the dependences (apk is Alpine Linux's # equivalent to apt) and then remove the cached files (to keep the image # as small as we can) RUN apk add --update bash build-base nodejs mariadb-dev tzdata && \ rm -rf /var/cache/apk/* # Make a directory to hold our app and set the working directory to it RUN mkdir /app WORKDIR /app # Do the gem installation stuff first, in a separate step, because they # Don't change as often as the code (so we can cache them in a separate # Docker image layer) COPY Gemfile Gemfile.lock ./ RUN bundle install --binstubs # Now copy the current folder to the WORKDIR and drop root privileges COPY . . RUN chown -R nobody:nogroup /app # Compile all assets RUN bundle exec rake assets:precompile # Inform Docker what port our container listens on at runtime EXPOSE 3000 # Set a default command to start the Rails server (can override this for workers, etc.) CMD ["bundle", "exec", "rails", "server", "-p", "3000"]
Build the Docker image and tag it
docker build -t <your_username>/k8s-sample-app:v0.1 .
Once this completes you can list all images using the
docker images command:
$ docker images REPOSITORY TAG IMAGE ID CREATED SIZE <your_username>/k8s-sample-app v0.1 104edfbbe440 2 minutes ago 617MB
To create a remote private repository, sign into Docker Hub, click on Repositories then Create Repository.
Log in via your local command line (to allow you to push):
docker login # enter Docker Hub username and press enter # enter Docker Hub password and press enter
Push the image to Docker Hub:
docker push <your_username>/k8s-sample-app:v0.1
After you've made some changes to your Rails app you will need to rebuild the image (ideally with a new tag) and then push it to Docker Hub.
docker build -t <your_username>/k8s-sample-app:v0.2 . docker push <your_username>/k8s-sample-app:v0.2