Nginx websocket proxy - regex

Question

I'm trying to use nginx to proxy websocket requests using a regularexpression as follows:
server {
listen 9092;
server_name ~^(?<pc_name>.*)\.(.*)$;
location / {
include proxy_params;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_pass http://$pc_name:9092;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;
}
}
map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}
and it's not working like that, i'm getting errors about not being able to resolve the host if i try to access pc-addr.localhost:9092 i get the error:
2017/08/07 08:42:37 [error] 22021#22021: *2 no resolver defined to resolve pc-addr, client: 127.0.0.1, server: ~^(?<pc_name>.*)\.(.*)$, request: "GET / HTTP/1.1", host: "pc-addr.localhost:9092"
However, if I replace the variable name with with pc-addr directly (i.e. all requests will be forwarded to pc-add:9092) it works fine and the requests are proxied as expected
server {
listen 9092;
server_name ~^(?<pc_name>.*)\.(.*)$;
location / {
include proxy_params;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header X-Forwarded-Proto $scheme;
proxy_pass http://pc-addr:9092;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection $connection_upgrade;
}
}
map $http_upgrade $connection_upgrade {
default upgrade;
'' close;
}