When moving from Passenger to Unicorn, a stale file
/etc/nginx/stack.conf is left behind, causing Passenger to continue running even though all requests are being handled by Unicorn.
The reason is because the recipes for Nginx/Passenger create the
stack.conf file, but there is no mechanism to remove the file when Passenger is no longer in use.
Create a custom Chef script to keep the
stack.conf file empty if you are using Passenger. For more information about using Chef in your environment see:
Customize Your Environment with Chef Recipes
Common Custom Chef Solutions