Public | Automated Build

Last pushed: 9 months ago
Short Description
This container for building various versions of the Ruby application using source-to-image.
Full Description

Ruby Docker image

This repository contains the source for building various versions of
the Ruby application as a reproducible Docker image using
The resulting image can be run using Docker.


To build a simple ruby-sample-app application
using standalone S2I and then run the
resulting image with Docker execute:

  • For CentOS based image
     $ s2i build --context-dir=2.4/test/puma-test-app/ thedigitalgarage/s2i-ruby:2.4 ruby-sample-app
     $ docker run -p 8080:8080 ruby-sample-app

Accessing the application:

$ curl

Repository organization

  • <ruby-version>

    • Dockerfile

      CentOS based Dockerfile.

    • s2i/bin/

      This folder contains scripts that are run by S2I:

      • assemble

        Used to install the sources into the location where the application
        will be run and prepare the application for deployment (eg. installing
        modules using bundler, etc.)

      • run

        This script is responsible for running the application by using the
        application web server.

      • usage*

        This script prints the usage of this image.

    • contrib/

      This folder contains a file with commonly used modules.

    • test/

      This folder contains a S2I
      test framework with a simple Rack server.

      • puma-test-app/

        Simple Puma web server used for testing purposes by the S2I test framework.

      • rack-test-app/

        Simple Rack web server used for testing purposes by the S2I test framework.

      • run

        Script that runs the S2I test framework.

Environment variables

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


    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


    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.


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


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


    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 Docker -e run flag:

     $ docker 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:

    • Shotgun
    • Rerun
    • Rack-livereload

      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 Docker -e run flag:

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

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

docker exec -it <CONTAINER_ID> /bin/bash

After you Docker 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 Docker run command:

$ docker 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:


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

$ docker 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.

Docker Pull Command
Source Repository