Nginx how to change the backend server by incoming parameters?

Question

Nginx

There is a server with nginx up.
How to redirect a request to another backend server (located in the same locale) by incoming parameters.
For example, we have the following request:
site.com/?event=show
server 192.168.0.1
should process this request But this request:
site.com/?event=write
another server should process it ( 192.168.0.2 )
Parameters are passed not only in get parameters, but also in post.
In what direction can you dig to deal with this?

Answer 1

if ($arg_event = show) {
  proxy_pass http://192.168.0.1;
}
if ($arg_event = write) {
  proxy_pass http://192.168.0.2;
}