Redmine, Ruby, Passenger-Phusion, and Nginx makes for an extremely confusing situation with dependencies, installation “instructions”, and “mismatching” package versions.
Redmine wants Ruby x, your Linux distribution has Ruby y, Passenger-Phusion only works with Ruby z, and you quite often end up in a loop somewhere. This article will not do anything to help that confusion I’m afraid.
On Passenger-Phusion’s website, there’s an interesting explanation as to why you need to let Passenger-Phusion build Nginx for you, unless you can actually use everything pre-packaged, which you cannot if you want to use Ubuntu 20.04.LTS and Redmine 4.1.
Before you begin, you should know that installing Passenger in its Nginx integration mode involves extending Nginx with code from Passenger. However, Nginx does not support loadable modules. This means that in order to install Passenger’s Nginx integration mode, it is necessary to recompile Nginx from source. And that is exactly what we will do in this installation guide.
Now, if you head on over to the Nginx blog, you can read:
NGINX Open Source 1.11.5 and NGINX Plus Release R11 introduced binary compatibility for dynamic modules. This article explains how to compile third‑party modules for use with NGINX Open Source and NGINX Plus in a development environment.
That statement was made for Nginx 1.11. They are, at the time of this writing, at 1.19.
So basically, if you want to run Redmine 4.1 on Ubuntu 20.04.LTS, which ships with Ruby 2.7, and a Passenger-Phusion module that requires Ruby 2.7, you’re on your own since Redmine 4.1 does not support Ruby 2.7. If you use RVM to installed Ruby 2.6.x, you need to manually handle Passenger-Phusion, which eventually requires re-compiling Nginx, regardless of it supporting “dynamic modules”.
There is one small glimmer of hope:
Installing Passenger as a normal or dynamic Nginx module
Using Ubuntu 18.04.LTS, the included Passenger, Nginx, and Ruby all work with Redmine 4.1.x, so that may be a smoother path to take before this is all “fixed”, if it gets fixed.