I'm confused what purpose Mongrel2 serves/provides that nginx doesn't already do.
(Yes, I've read the manual but I must to be too much of a noob to understand how it's fundamentally different than nginx)
My current web application stack is:
- nginx: webserver
- Lua: programming language
- FastCGI + LuaJIT: to connect nginx to Lua
- Postgres: database
If you could only name one thing then it would be that Mongrel2 is build around ZeroMQ which means that scaling your web server has never been easier.
If a request comes in, Mongrel2 receives it (nothing unusual here, same as for NginX and any other httpd). Next thing that happens is that Mongrel2 distributes the task of compiling a response to n (ZeroMQ-enabled) backends, waits for them to do the work, receives results, compiles the response and sends it off to the client.
Now, the magic is with the fact that n can be any number and, that each of n can be written in any language as supported by ZeroMQ (20 or so) plus, all goes across the network so each n can be a dedicated box, possibly in another datacenter.
In other words: with NginX and all the rest you have to do scalability in your logic tier, Mongrel2 allows you to start (from a request/response cycle point of view) this right where the request hits your infrastructure, at the httpd rather than letting complexity penetrate down to your logic tier which blows complexity upwards by at least one order of magnitude imo.