Nginx url GET parameter with proxy

i url in nginx server:

http://mynginx.com/proxy?url=http://target.com

and want proxy through nginx server, retrieves http://target.com

i using in nginx configuration:

location /proxy { proxy_pass $arg_url proxy_set_header host $host; }

for reason response "502 bad gateway"

can tell appropiate configuration problem?

and why nginx response 502 error?

thanks in advance.

my bad, not using resolver in configuration:

location /proxy { resolver 8.8.8.8; proxy_pass $arg_url proxy_set_header host $host; }

url nginx proxy get

Three