Using the Ruby Runtime with Serverless Functions

The Ruby Runtime is used by Vercel to compile Ruby Serverless Functions that define a singular HTTP handler from .rb files within an /api directory at your project's root.

Ruby files must have one of the following variables defined:

• Handler proc that matches the do |request, response| signature.
• Handler class that inherits from the WEBrick::HTTPServlet::AbstractServlet class.

For example, define a index.rb file inside a /api directory as follows:

require 'cowsay'
 
Handler = Proc.new do |request, response|
  name = request.query['name'] || 'World'
 
  response.status = 200
  response['Content-Type'] = 'text/text; charset=utf-8'
  response.body = Cowsay.say("Hello #{name}", 'cow')
end

An example index.rb file inside an /api directory.

Inside a Gemfile define:

source "https://rubygems.org"
 
gem "cowsay", "~> 0.3.0"

An example Gemfile file that defines cowsay as a dependency.

New deployments use Ruby 2.7.x as the default version.

You can specify the version of Ruby by defining ruby in a Gemfile, like so:

source "https://rubygems.org"
ruby "~> 2.7.x"

When defining a Ruby version, the following Ruby versions can be selected:

• 2.7.x (default)
• 2.5.x (disabled since November 30th 2021)

This Runtime supports installing dependencies defined in the Gemfile. Alternatively, dependencies can be vendored with the bundler install --deployment command (useful for gems that require native extensions). In this case, dependencies are not built on deployment.