Ruby

Railpack builds and deploys Ruby applications with support for several language-specific tools and frameworks.

Detection

Your project is detected as a Ruby application if a Gemfile is present in the root directory.

Versions

The Ruby version is determined in the following order:

• Set via the RAILPACK_RUBY_VERSION environment variable
• Read from the .ruby-version file
• Read from the Gemfile file
• Read from mise-compatible version files (.tool-versions, mise.toml)
• Defaults to 3.4.6

Runtime Variables

These variables are available at runtime:

BUNDLE_GEMFILE="/app/Gemfile"
GEM_PATH="/usr/local/bundle"
GEM_HOME= "/usr/local/bundle"
MALLOC_ARENA_MAX="2"

Configuration

Railpack builds your Ruby application based on your project structure. The build process:

• Installs Ruby and required system dependencies
• Installs project dependencies
• Configures the Ruby environment for production

The start command is determined by:

1. Framework-specific start command (see below)
2. config/environment.rb file
3. config.ru file
4. Rakefile file

Config Variables

Variable	Description	Example
RAILPACK_RUBY_VERSION	Override the Ruby version	3.4.2

Framework Support

Railpack detects and configures caches and commands for popular frameworks:

Rails

Railpack detects Rails projects by:

• Presence of config/application.rb

Databases

Railpack automatically installs system dependencies for common databases:

• PostgreSQL: Installs libpq-dev
• MySQL: Installs default-libmysqlclient-dev
• Magick: Installs imagemagick
• Vips: Installs libvips-dev
• Charlock Holmes: Installs libicu-dev