It's vital to distinguish between these Rack-based application (or "web app") servers and Nginx which acts as the public web front-end for Cloud 66 applications. We usually refer to Nginx as our "web server", but it performs a different task to the Rack-based app servers described in this doc.
Migrating between application servers
You need to choose your web app / Rack server when you first build an application. Changes to or from Passenger will not be applied after your application has initially been built. You can however change freely between other supported servers after build.
Configuring a custom Rack server
If you would like to use a different server, there are some points you'd need to consider for it to work with a Cloud 66 application. These conventions will allow Cloud 66 to redirect traffic to your servers and manage them for availability, memory consumption and restart cycles.
For the traffic to be redirected to your web app server, it should use a Unix socket at
For the web app server to be managed and restarted properly by Cloud 66, it needs to have it's PID file at