Rack Application Behavior on Heroku
Last updated September 17, 2024
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Table of Contents
Rack applications behave like Ruby applications with the following additions.
Auto-Detection
A root-level config.ru file specifies the existence of a Rack application. When Heroku recognizes a deployed app as a Rack application, we respond with -----> Ruby/Rack app detected at deploy time.
$ git push heroku main
-----> Ruby/Rack app detected
Config Vars
We set the following environment variables, in addition to the ones we set for Ruby Application Behavior on all Ruby apps.
RACK_ENV=> “production”
Add-ons
Adds the same add-ons as a pure Ruby app.
Process Types
If you don’t include a Procfile, Rack apps define a web process type at deploy time:
web: bundle exec rackup config.ru -p $PORT
On Heroku, we recommend Puma as the webserver. Regardless of the webserver you choose, always specify the webserver explicitly in the Procfile on production apps.
As a special case to assist in migration from Bamboo, Ruby apps that bundle the thin gem get this web process type:
web: bundle exec thin start -R config.ru -e $RACK_ENV -p $PORT