upstream keepalive connections for all servers or each server?

[fengx]

Hi 

As known, the keepalive directive can activate the connections cache for
upstream servers. I know the connection pool is in each worker process. But
I'ms confused that the connection number is for each upstream server or is
shared for all servers? It's documented at
http://nginx.org/en/docs/http/ngx_http_upstream_module.html#keepalive 

Thanks
Xiaofeng

Posted at Nginx Forum: https://forum.nginx.org/read.php?2,274098,274098#msg-274098