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Ruby 3.0 container image

This container image includes Ruby 3.0 as a S2I base image for your Ruby 3.0 applications. Users can choose between RHEL, CentOS and Fedora based builder images. The RHEL images are available in the Red Hat Container Catalog, the CentOS images are available on Quay.io, and the Fedora images are available in Quay.io. The resulting image can be run using podman.

Note: while the examples in this README are calling podman, you can replace any such calls by docker with the same arguments

Description

Ruby 3.0 available as container is a base platform for building and running various Ruby 3.0 applications and frameworks. Ruby is the interpreted scripting language for quick and easy object-oriented programming. It has many features to process text files and to do system management tasks (as in Perl). It is simple, straight-forward, and extensible.

This container image includes an npm utility, so users can use it to install JavaScript modules for their web applications. There is no guarantee for any specific npm or nodejs version, that is included in the image; those versions can be changed anytime and the nodejs itself is included just to make the npm work.

Usage in Openshift

For this, we will assume that you are using the ubi9/ruby-30 image, available via ruby:3.0 imagestream tag in Openshift. Building a simple ruby-sample-app application in Openshift can be achieved with the following step:

```
oc new-app ruby:3.0~https://github.com/sclorg/rails-ex.git
```

Accessing the application:

$ oc get pods
$ oc exec <pod> -- curl 127.0.0.1:8080

Source-to-Image framework and scripts

This image supports the Source-to-Image (S2I) strategy in OpenShift. The Source-to-Image is an OpenShift framework which makes it easy to write images that take application source code as an input, use a builder image like this Ruby container image, and produce a new image that runs the assembled application as an output.

To support the Source-to-Image framework, important scripts are included in the builder image:

  • The /usr/libexec/s2i/assemble script inside the image is run to produce a new image with the application artifacts. The script takes sources of a given application and places them into appropriate directories inside the image. It utilizes some common patterns in Ruby application development (see the Environment variables section below).
  • The /usr/libexec/s2i/run script is set as the default command in the resulting container image (the new image with the application artifacts). It configures web server and runs this server on port 8080.

Building an application using a Dockerfile

Compared to the Source-to-Image strategy, using a Dockerfile is a more flexible way to build a Ruby container image with an application. Use a Dockerfile when Source-to-Image is not sufficiently flexible for you or when you build the image outside of the OpenShift environment.

To use the Ruby image in a Dockerfile, follow these steps:

1. Pull a base builder image to build on

podman pull ubi9/ruby-30

An RHEL7 image ubi9/ruby-30 is used in this example.

2. Pull and application code

An example application available at https://github.com/sclorg/rails-ex.git is used here. Feel free to clone the repository for further experiments.

git clone https://github.com/sclorg/rails-ex.git app-src

3. Prepare an application inside a container

This step usually consists of at least these parts:

  • putting the application source into the container
  • installing the dependencies
  • setting the default command in the resulting image

For all these three parts, users can use the Source-to-Image scripts inside the image (3.1.), or users can either setup all manually and use commands ruby, bundle and rackup explicitly in the Dockerfile (3.2.)

3.1 To use the Source-to-Image scripts and build an image using a Dockerfile, create a Dockerfile with this content:
FROM ubi9/ruby-30

# Add application sources to a directory that the assemble scriptexpects them
# and set permissions so that the container runs without root access
USER 0
ADD app-src /tmp/src
RUN chown -R 1001:0 /tmp/src
USER 1001

# Set up development mode
ENV RAILS_ENV=development

# Install the dependencies
RUN /usr/libexec/s2i/assemble

# Set the default command for the resulting image
CMD /usr/libexec/s2i/run

The s2i scripts are used to set-up and run common Ruby applications. More information about the scripts can be found in Source-to-Image section.

3.2 To use your own setup, create a Dockerfile with this content:
FROM ubi9/ruby-30

USER 0
ADD app-src ./
RUN bundle install --path ./bundle

CMD bundle exec "rackup -P /tmp/rack.pid --host 0.0.0.0 --port 8080"

4. Build a new image from a Dockerfile prepared in the previous step

podman build -t ruby-app .

5. Run the resulting image with final application

podman run -d ruby-app

Environment variables

To set these environment variables, you can place them as a key value pair into a .s2i/environment file inside your source code repository.

  • RACK_ENV

    This variable specifies the environment where the Ruby application will be deployed (unless overwritten) - production, development, test. Each level has different behaviors in terms of logging verbosity, error pages, ruby gem installation, etc.

    Note: Application assets will be compiled only if the RACK_ENV is set to production

  • DISABLE_ASSET_COMPILATION

    This variable set to true indicates that the asset compilation process will be skipped. Since this only takes place when the application is run in the production environment, it should only be used when assets are already compiled.

  • PUMA_MIN_THREADS, PUMA_MAX_THREADS

    These variables indicate the minimum and maximum threads that will be available in Puma's thread pool.

  • PUMA_WORKERS

    This variable indicate the number of worker processes that will be launched. See documentation on Puma's clustered mode.

  • RUBYGEM_MIRROR

    Set this variable to use a custom RubyGems mirror URL to download required gem packages during build process.

Hot deploy

In order to dynamically pick up changes made in your application source code, you need to make following steps:

  • For Ruby on Rails applications

    Run the built Rails image with the RAILS_ENV=development environment variable passed to the podman -e run flag:

    $ podman run -e RAILS_ENV=development -p 8080:8080 rails-app

  • For other types of Ruby applications (Sinatra, Padrino, etc.)

    Your application needs to be built with one of gems that reloads the server every time changes in source code are done inside the running container. Those gems are:

    Please note that in order to be able to run your application in development mode, you need to modify the S2I run script, so the web server is launched by the chosen gem, which checks for changes in the source code.

    After you built your application image with your version of S2I run script, run the image with the RACK_ENV=development environment variable passed to the podman -e run flag:

    $ podman run -e RACK_ENV=development -p 8080:8080 sinatra-app

To change your source code in running container, use Podman's exec command:

$ podman exec -it <CONTAINER_ID> /bin/bash

After you podman exec into the running container, your current directory is set to /opt/app-root/src, where the source code is located.

Performance tuning

You can tune the number of threads per worker using the PUMA_MIN_THREADS and PUMA_MAX_THREADS environment variables. Additionally, the number of worker processes is determined by the number of CPU cores that the container has available, as recommended by Puma's documentation. This is determined using the cgroup cpusets subsystem. You can specify the cores that the container is allowed to use by passing the --cpuset-cpus parameter to the podman run command:

$ podman run -e PUMA_MAX_THREADS=32 --cpuset-cpus='0-2,3,5' -p 8080:8080 sinatra-app

The number of workers is also limited by the memory limit that is enforced using cgroups. The builder image assumes that you will need 50 MiB as a base and another 15 MiB for every worker process plus 128 KiB for each thread. Note that each worker has its own threads, so the total memory required for the whole container is computed using the following formula:

50 + 15 * WORKERS + 0.125 * WORKERS * PUMA_MAX_THREADS

You can specify a memory limit using the --memory flag:

$ podman run -e PUMA_MAX_THREADS=32 --memory=300m -p 8080:8080 sinatra-app

If memory is more limiting then the number of available cores, the number of workers is scaled down accordingly to fit the above formula. The number of workers can also be set explicitly by setting PUMA_WORKERS.

See also

Dockerfile and other sources are available on https://github.com/sclorg/s2i-ruby-container. In that repository you also can find another versions of Ruby environment Dockerfiles. Dockerfile for RHEL8 it's Dockerfile.rhel8, for RHEL9 it's Dockerfile.rhel9 and the Fedora Dockerfile is called Dockerfile.fedora.