Nginx: cache only specific urls and named location - nginx

Question

I have rails application. There are parts of nginx config of it:
upstream app_server {
server unix:/var/www/app/shared/unicorn.sock fail_timeout=0;
}
server {
listen 80;
server_name app hostname;
keepalive_timeout 5;
root /var/www/app/current/public;
try_files $uri/index.html $uri.html $uri #app;
location #app {
proxy_pass http://app_server;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $http_host;
proxy_redirect off;
proxy_cache off;
}
location ~ /assets/*\.(png|gif|jpg|jpeg|css|js|swf|ico|gz)(\?[0-9]+)?$ {
access_log off;
}
}
I want to cache several pages of my apps (for example all *.json urls). How I can do that?
According to nginx docs I can't:
use nested location in named location
use proxy_cache in if block

Answer 1

You can get away with adding Json to the extensions in the static file block if they are not virtual URLs.
If they are, you need to either setup differently by forwarding everything to your app by default and making exceptions, so you avoid having to use named locations. Or you can set variables based on if statements inside the named location:
location #app {
set $proxy_cache_cfg "off";
if($request_uri ~ \.json$) {
set $proxy_cache_cfg "json_zone";
}
}
Untested, not sure if "off" should be quoted and whether it even would work here. If this won't work, you can always use the reverse approach and set proxy_no_cache based on a variable, since that is in effect for anything non-empty and non-zero.