Nginxでディレクトリでサブドメインを切りながら共通エラーページを制御します．

fastcgi.conf

:
error_page                        404 = @404;
error_page                        500 = @500;
error_page                        502 = @502;
:

nginx.conf

http {
  :
  upstream  404 { server  localhost:404; }
  upstream  500 { server  localhost:500; }
  upstream  502 { server  localhost:502; }
  :
}

server.conf

# ------------ #
# DOMAINS      #
# ------------ #
server {
  listen       80;
  charset      UTF-8;
  server_name  example.com
               example.net;
  rewrite      ^  http://www.$host;
}

# ------------ #
# SUBDOMAINS   #
# ------------ #
server {
  listen       80;
  charset      UTF-8;
  server_name  ~^(.+)\.(example\.com)$
               ~^(.+)\.(example\.net)$;
  set          $subdomain $1;
  set          $hostbase  $2;
  root         /var/www/domains/$hostbase/$subdomain/web;
  # IF www.example.com THEN ROOT IS /var/www/domain/example.com/www/web/index.php
  # IF app.example.net THEN ROOT IS /var/www/domain/example.net/app/web/index.php
  access_log   /var/log/nginx/domains.a.log;
  error_log    /var/log/nginx/domains.e.log;
  location / {
    index  index.php index.html;
    if (-f $request_filename) {
      #expires  7d;
      break;
    }
    if (-f $request_filename/index.php) {
      rewrite  ^(.*) $uri/index.php last;
      break;
    }
    if (-f $document_root/index.php) {
      rewrite  ^(.*) /index.php last;
      break;
    }
  }
  location @404 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://404;
  }
  location @500 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://500;
  }
  location @502 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://502;
  }
  location ~* \.php$ {
    fastcgi_pass   localhost:9000;
    include        /etc/nginx/conf.d/fastcgi.conf;
  }
}

# ------------ #
# NODE SERVER  #
# ------------ #
upstream node {
  server  localhost:3000;
}
server {
  listen       80;   
  charset      UTF-8;
  server_name  node.example.com;
  location @404 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://404;
  }
  location @500 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://500;
  }
  location @502 {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://502;
  }
  location / {
    include     /etc/nginx/conf.d/proxy.conf;
    proxy_pass  http://node;
  }
}

# ------------ #
# ERROR SERVER #
# ------------ #
server {
  listen       404;
  listen       500;
  listen       502;
  root         /var/www/apps/error;
  location / {
    index  index.php;
    if ($server_port = 404) {
      rewrite  ^.* /index.php?e=404 last;
      return 404;
    }
    if ($server_port = 500) {
      rewrite  ^.* /index.php?e=500 last;
      return 500;
    }
    if ($server_port = 502) {
      rewrite  ^.* /index.php?e=502 last;
      return 502;
    }
  }
  location ~* \.php$ {
    fastcgi_pass   localhost:9000;
    include        /etc/nginx/conf.d/fastcgi.conf;
  }
}