Использую функцию поддержки DNS от masterhost где вписаны записи A на сервер c IP к примеру 1.2.3.4 на котором стоит nginx, который обрабатывает и проксирует запросы пользователей на сервер с ип 4.3.2.1 на котором стоит сервер apache. Все порты на INPUT коннекты блокируются по средству iptables. ServerName в конфиге apache прописан, в nginx server_name тоже прописан. И при нажатии некоторых ссылок к примеру:
http://домен/forum1/showthread.php?goto=newpost&t=1
http://домен/forum1/member.php?find=lastposter&f=2
http://домен/forum1/forumdisplay.php?do=markread
они преобразуются в IP
http://1.2.3.4/forum1/showthread.php?goto=newpost&t=1
http://1.2.3.4/forum1/member.php?find=lastposter&f=2
http://1.2.3.4/forum1/forumdisplay.php?do=markread

В настройках форума адрес с доменом прописан?

fdeadalf, конфиги апача и nginx'a в студию, телепатов тут нет

Конфиг nginx

#user nobody;
worker_processes 1;

#error_log logs/error.log;
#error_log logs/error.log notice;
#error_log logs/error.log info;

#pid logs/nginx.pid;


events {
worker_connections 1024;
}


http {
include mime.types;
default_type application/octet-stream;

#log_format main '$remote_addr - $remote_user [$time_local] "$request" '
# '$status $body_bytes_sent "$http_referer" '
# '"$http_user_agent" "$http_x_forwarded_for"';

#access_log logs/access.log main;

sendfile on;
#tcp_nopush on;

#keepalive_timeout 0;
keepalive_timeout 65;

#gzip on;

server {
listen 80;
server_name домен;

#charset koi8-r;

#access_log logs/host.access.log main;

location / {
#root html;
index index.html index.htm index.php;
}

#error_page 404 /404.html;

# redirect server error pages to the static page /50x.html
#
error_page 500 502 503 504 /50x.html;
location = /50x.html {
root html;
}

# proxy the PHP scripts to Apache listening on 127.0.0.1:80
#
location ~ \.php$ {
proxy_pass http://1.2.3.4:80;
}

# pass the PHP scripts to FastCGI server listening on 127.0.0.1:9000
#
#location ~ \.php$ {
# root html;
# fastcgi_pass 127.0.0.1:9000;
# fastcgi_index index.php;
# fastcgi_param SCRIPT_FILENAME /scripts$fastcgi_script_name;
# include fastcgi_params;
#}

# deny access to .htaccess files, if Apache's document root
# concurs with nginx's one
#
#location ~ /\.ht {
# deny all;
#}
}


# another virtual host using mix of IP-, name-, and port-based configuration
#
#server {
# listen 8000;
# listen somename:8080;
# server_name somename alias another.alias;

# location / {
# root html;
# index index.html index.htm;
# }
#}


# HTTPS server
#
#server {
# listen 443;
# server_name localhost;

# ssl on;
# ssl_certificate cert.pem;
# ssl_certificate_key cert.key;

# ssl_session_timeout 5m;

# ssl_protocols SSLv2 SSLv3 TLSv1;
# ssl_ciphers ALL:!ADH:!EXPORT56:RC4+RSA:+HIGH:+MEDIUM:+LOW:+SSLv2:+EXP;
# ssl_prefer_server_ciphers on;

# location / {
# root html;
# index index.html index.htm;
# }
#}

}

Конфиг apache

#
# Based upon the NCSA server configuration files originally by Rob McCool.
#
# This is the main Apache server configuration file. It contains the
# configuration directives that give the server its instructions.
# See http://httpd.apache.org/docs/2.2/ for detailed information about
# the directives.
#
# Do NOT simply read the instructions in here without understanding
# what they do. They're here only as hints or reminders. If you are unsure
# consult the online docs. You have been warned.
#
# The configuration directives are grouped into three basic sections:
# 1. Directives that control the operation of the Apache server process as a
# whole (the 'global environment').
# 2. Directives that define the parameters of the 'main' or 'default' server,
# which responds to requests that aren't handled by a virtual host.
# These directives also provide default values for the settings
# of all virtual hosts.
# 3. Settings for virtual hosts, which allow Web requests to be sent to
# different IP addresses or hostnames and have them handled by the
# same Apache server process.
#
# Configuration and logfile names: If the filenames you specify for many
# of the server's control files begin with "/" (or "drive:/" for Win32), the
# server will use that explicit path. If the filenames do *not* begin
# with "/", the value of ServerRoot is prepended -- so "/var/log/apache2/foo.log"
# with ServerRoot set to "" will be interpreted by the
# server as "//var/log/apache2/foo.log".
#

### Section 1: Global Environment
#
# The directives in this section affect the overall operation of Apache,
# such as the number of concurrent requests it can handle or where it
# can find its configuration files.
#

#
# ServerRoot: The top of the directory tree under which the server's
# configuration, error, and log files are kept.
#
# NOTE! If you intend to place this on an NFS (or otherwise network)
# mounted filesystem then please read the LockFile documentation (available
# at <URL:http://httpd.apache.org/docs-2.1/mod/mpm_common.html#lockfile>);
# you will save yourself a lot of trouble.
#
# Do NOT add a slash at the end of the directory path.
#
ServerRoot "/etc/apache2"
ServerName домен


#
# The accept serialization lock file MUST BE STORED ON A LOCAL DISK.
#
#<IfModule !mpm_winnt.c>
#<IfModule !mpm_netware.c>
LockFile /var/lock/apache2/accept.lock
#</IfModule>
#</IfModule>

#
# PidFile: The file in which the server should record its process
# identification number when it starts.
# This needs to be set in /etc/apache2/envvars
#
PidFile ${APACHE_PID_FILE}

#
# Timeout: The number of seconds before receives and sends time out.
#
Timeout 300

#
# KeepAlive: Whether or not to allow persistent connections (more than
# one request per connection). Set to "Off" to deactivate.
#
KeepAlive On

#
# MaxKeepAliveRequests: The maximum number of requests to allow
# during a persistent connection. Set to 0 to allow an unlimited amount.
# We recommend you leave this number high, for maximum performance.
#
MaxKeepAliveRequests 100

#
# KeepAliveTimeout: Number of seconds to wait for the next request from the
# same client on the same connection.
#
KeepAliveTimeout 15

##
## Server-Pool Size Regulation (MPM specific)
##

# prefork MPM
# StartServers: number of server processes to start
# MinSpareServers: minimum number of server processes which are kept spare
# MaxSpareServers: maximum number of server processes which are kept spare
# MaxClients: maximum number of server processes allowed to start
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_prefork_module>
StartServers 5
MinSpareServers 5
MaxSpareServers 10
MaxClients 150
MaxRequestsPerChild 0
</IfModule>

# worker MPM
# StartServers: initial number of server processes to start
# MaxClients: maximum number of simultaneous client connections
# MinSpareThreads: minimum number of worker threads which are kept spare
# MaxSpareThreads: maximum number of worker threads which are kept spare
# ThreadsPerChild: constant number of worker threads in each server process
# MaxRequestsPerChild: maximum number of requests a server process serves
<IfModule mpm_worker_module>
StartServers 2
MaxClients 150
MinSpareThreads 25
MaxSpareThreads 75
ThreadsPerChild 25
MaxRequestsPerChild 0
</IfModule>

# These need to be set in /etc/apache2/envvars
User ${APACHE_RUN_USER}
Group ${APACHE_RUN_GROUP}

#
# AccessFileName: The name of the file to look for in each directory
# for additional configuration directives. See also the AllowOverride
# directive.
#

AccessFileName .htaccess

#
# The following lines prevent .htaccess and .htpasswd files from being
# viewed by Web clients.
#
<Files ~ "^\.ht">
Order allow,deny
Deny from all
</Files>

#
# DefaultType is the default MIME type the server will use for a document
# if it cannot otherwise determine one, such as from filename extensions.
# If your server contains mostly text or HTML documents, "text/plain" is
# a good value. If most of your content is binary, such as applications
# or images, you may want to use "application/octet-stream" instead to
# keep browsers from trying to display binary files as though they are
# text.
#
DefaultType text/plain


#
# HostnameLookups: Log the names of clients or just their IP addresses
# e.g., www.apache.org (on) or 204.62.129.132 (off).
# The default is off because it'd be overall better for the net if people
# had to knowingly turn this feature on, since enabling it means that
# each client request will result in AT LEAST one lookup request to the
# nameserver.
#
HostnameLookups Off

# ErrorLog: The location of the error log file.
# If you do not specify an ErrorLog directive within a <VirtualHost>
# container, error messages relating to that virtual host will be
# logged here. If you *do* define an error logfile for a <VirtualHost>
# container, that host's errors will be logged there and not here.
#
ErrorLog /var/log/apache2/error.log

#
# LogLevel: Control the number of messages logged to the error_log.
# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
#
LogLevel warn

# Include module configuration:
Include /etc/apache2/mods-enabled/*.load
Include /etc/apache2/mods-enabled/*.conf

# Include all the user configurations:
Include /etc/apache2/httpd.conf

# Include ports listing
Include /etc/apache2/ports.conf

#
# The following directives define some format nicknames for use with
# a CustomLog directive (see below).
# If you are behind a reverse proxy, you might want to change %h into %{X-Forwarded-For}i
#
LogFormat "%v:%p %h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" vhost_combined
LogFormat "%h %l %u %t \"%r\" %>s %b \"%{Referer}i\" \"%{User-Agent}i\"" combined
LogFormat "%h %l %u %t \"%r\" %>s %b" common
LogFormat "%{Referer}i -> %U" referer
LogFormat "%{User-agent}i" agent

#
# Define an access log for VirtualHosts that don't define their own logfile
CustomLog /var/log/apache2/other_vhosts_access.log vhost_combined

#
# Customizable error responses come in three flavors:
# 1) plain text 2) local redirects 3) external redirects
#
# Some examples:
#ErrorDocument 500 "The server made a boo boo."
#ErrorDocument 404 /missing.html
#ErrorDocument 404 "/cgi-bin/missing_handler.pl"
#ErrorDocument 402 http://www.example.com/subscription_info.html
#

#
# Putting this all together, we can internationalize error responses.
#
# We use Alias to redirect any /error/HTTP_<error>.html.var response to
# our collection of by-error message multi-language collections. We use
# includes to substitute the appropriate text.
#
# You can modify the messages' appearance without changing any of the
# default HTTP_<error>.html.var files by adding the line:
#
# Alias /error/include/ "/your/include/path/"
#
# which allows you to create your own set of files by starting with the
# /usr/share/apache2/error/include/ files and copying them to /your/include/path/,
# even on a per-VirtualHost basis. The default include files will display
# your Apache version number and your ServerAdmin email address regardless
# of the setting of ServerSignature.
#
# The internationalized error documents require mod_alias, mod_include
# and mod_negotiation. To activate them, uncomment the following 30 lines.

# Alias /error/ "/usr/share/apache2/error/"
#
# <Directory "/usr/share/apache2/error">
# AllowOverride None
# Options IncludesNoExec
# AddOutputFilter Includes html
# AddHandler type-map var
# Order allow,deny
# Allow from all
# LanguagePriority en cs de es fr it nl sv pt-br ro
# ForceLanguagePriority Prefer Fallback
# </Directory>
#
# ErrorDocument 400 /error/HTTP_BAD_REQUEST.html.var
# ErrorDocument 401 /error/HTTP_UNAUTHORIZED.html.var
# ErrorDocument 403 /error/HTTP_FORBIDDEN.html.var
# ErrorDocument 404 /error/HTTP_NOT_FOUND.html.var
# ErrorDocument 405 /error/HTTP_METHOD_NOT_ALLOWED.html.var
# ErrorDocument 408 /error/HTTP_REQUEST_TIME_OUT.html.var
# ErrorDocument 410 /error/HTTP_GONE.html.var
# ErrorDocument 411 /error/HTTP_LENGTH_REQUIRED.html.var
# ErrorDocument 412 /error/HTTP_PRECONDITION_FAILED.html.var
# ErrorDocument 413 /error/HTTP_REQUEST_ENTITY_TOO_LARGE.html.var
# ErrorDocument 414 /error/HTTP_REQUEST_URI_TOO_LARGE.html.var
# ErrorDocument 415 /error/HTTP_UNSUPPORTED_MEDIA_TYPE.html.var
# ErrorDocument 500 /error/HTTP_INTERNAL_SERVER_ERROR.html.var
# ErrorDocument 501 /error/HTTP_NOT_IMPLEMENTED.html.var
# ErrorDocument 502 /error/HTTP_BAD_GATEWAY.html.var
# ErrorDocument 503 /error/HTTP_SERVICE_UNAVAILABLE.html.var
# ErrorDocument 506 /error/HTTP_VARIANT_ALSO_VARIES.html.var



# Include of directories ignores editors' and dpkg's backup files,
# see README.Debian for details.

# Include generic snippets of statements
Include /etc/apache2/conf.d/

# Include the virtual host configurations:
Include /etc/apache2/sites-enabled/

Виртуалхосты апатча

<VirtualHost *:80>
ServerAdmin webmaster@localhost
ServerName домен
ServerAlias домены

DocumentRoot /var/www/
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www/>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>

ScriptAlias /cgi-bin/ /usr/lib/cgi-bin/
<Directory "/usr/lib/cgi-bin">
AllowOverride None
Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
Order allow,deny
Allow from all
</Directory>

ErrorLog /var/log/apache2/error.log

# Possible values include: debug, info, notice, warn, error, crit,
# alert, emerg.
LogLevel warn

CustomLog /var/log/apache2/access.log combined

Alias /doc/ "/usr/share/doc/"
<Directory "/usr/share/doc/">
Options Indexes MultiViews FollowSymLinks
AllowOverride None
Order deny,allow
Deny from all
Allow from 127.0.0.0/255.0.0.0 ::1/128
</Directory>

</VirtualHost>

fdeadalf, хм. Я бы сделал бы вот так, nginx.conf

location ~\.php($|\/) {
           try_files $uri @apache;
           }

location @apache {
           internal;
           proxy_pass http://127.0.0.1:8080;
           proxy_set_header Host $host;
           proxy_set_header X-Real-IP $remote_addr;
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           client_max_body_size 20M;
           proxy_connect_timeout 90;
           proxy_send_timeout 90;
           proxy_read_timeout 90;
           proxy_send_lowat 12000;
           proxy_buffer_size 8k;
           proxy_buffers  32 64k;
           proxy_busy_buffers_size 64k;
           proxy_temp_file_write_size 64k;
           proxy_temp_path /var/tmp/nginx;
           }

Принцип прост и банален - локейшены (а они могут быть и вложенными, к примеру, после проверки доступа к adminpanel) при совпадении условия отправляют запрос на именованный локейшен @apache, а дальше на проксю.
Если у меня такое условие одно, то мне нет смысла заморачиваться на именованные локейшены и конфиг упрощается до такого

location ~\.php($|\/) {
           proxy_pass http://127.0.0.1:8080;
           proxy_set_header Host $host;
           proxy_set_header X-Real-IP $remote_addr;
           proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
           client_max_body_size 20M;
           proxy_connect_timeout 90;
           proxy_send_timeout 90;
           proxy_read_timeout 90;
           proxy_send_lowat 12000;
           proxy_buffer_size 8k;
           proxy_buffers  32 64k;
           proxy_busy_buffers_size 64k;
           proxy_temp_file_write_size 64k;
           proxy_temp_path /var/tmp/nginx;
           }

Есно, чт это кусок конфига, для понимания сути, а не бездумного копирования.

В апаче же нужно проверить, установлен ли mod_rpaf, и если нужно - установить и настроить (всего пять строк конфига)

LoadModule rpaf_module        libexec/apache22/mod_rpaf.so

RPAFenable On
RPAFsethostname On
RPAFproxy_ips 127.0.0.1
RPAFheader X-Forwarded-For

Вроде все.

PS: .htaccess и прочее рекомендую все же закрывать. Делается примерно так

location ~ /(\.ht|\.ft|\.svn) {
	deny  all;
	}