8. one Apache child must be enough for everyone

(read must be enough for most of the cases)

Why? Because most of the cases = one cpu, one disk and one ram. Running more Apache children on such a machine is just a waste of resources. The cpu or disk can not work better than 100%. Only sw developers can do better then 100% becase they have to! ;-)

The "normal" approach is to fork as many mod_perl Apache childs as the ram allows to be able to handle as many requests as possible. This was due to the fakt that Apache was processing the whole request(s) from client. This includes the connect, receive request, process request and send response. If we could strip this to the "process" step then we need just one process keeping busy all the resources of hw.

The way how to outsource the client communication somewhere else is to have a light weight reverse proxy. ba.pm.org is using nginx to deliver all the static content and proxy to Apache the only dynamic part and that is the feedback form submit processing.

What nginx does is that it fetches all the client request (can be big and long lasting in case of file uploads) and only when it is finished passes it to the Apache. Then when Apache is finished it pass the whole response to nginx and then it's ready to process another request. While nginx (slowly) let the client download the response.

Nginx is made lightweight, fast to deliver either static content or proxy for the dynamic one.

Let's have a look at the nginx config of ba.pm.org:

# bratislava.pm.org
server {
    listen       80;
    server_name  ba.pm.org;

    access_log /var/log/nginx/bratislava.pm-access.log;
	
    location / {
        rewrite  ^(.*)$  http://bratislava.pm.org$1  permanent;
    }		
}
server {
    listen       80;
    server_name  bratislava.pm.org;

    access_log /var/log/nginx/bratislava.pm-access.log;
	
    location / {
        root   /data/www/pm;
        index  index.html index.htm;
    }
	
    location /cgi/cgi-bin/ {
        proxy_pass        http://internal-hostname:81;
        proxy_set_header  X-Real-IP  $remote_addr;
        proxy_set_header Host $http_host;
        proxy_set_header X-Forwarded-Host $http_host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
   }

    location ~* \.(jpg|jpeg|gif|css|png|js|ico|rdf)$ {
        root   /data/www/pm;
        expires           1h;
    }
}

The site is ready to handle 1024 simultaneous connections and to receive a lot of feedback. ;-)

So? If you are not "everyone" and the Perl is doing other things than local IO, one Apache child is not enough. But nginx helps to decrease this number for a low price.