X-Powered-By' from the HTTP headers. When using Nginx, it can be using a simple setting. The setting has to be in http section and it takes the following form.
For example, if it is a FastCGI server the configuration setting will be as follows:
If you are using Nginx as a load balancer, the configuration setting will be as follows:
Unfortunately this configuration setting is not available yet in Passenger because Passenger is a thord party module and they have not implemented it yet.