NAME
   Net::DNAT - Psuedo Layer7 Packet Processer

SYNOPSIS
     use Net::DNAT;

     run Net::DNAT <settings...>;

DESCRIPTION
   This module is intended to be used for testing applications designed for
   load balancing systems. It listens on specified ports and forwards the
   incoming connections to the appropriate remote applications. The remote
   application can be on a separate machine or on the same machine
   listening on a different port and/or address.

SETTINGS
 port

   Specify which port or ports to listen on. See the Net::Server manpage
   for more details on the port setting and other Net::Server settings
   which may also be used with Net::DNAT.

    Example: port => 80

 user

   User to switch to once the server starts. (Just used by Net::Server)

    Example: user => "nobody"

 group

   Group to switch to once the server starts. (Just used by Net::Server)

    Example: group => "nobody"

 pools

   Supply a hash ref of pool definitions. The key in the hash is the pool
   name. Its value is either one destination scalar or an array ref of one
   or more destinations. If you just specify the destination value instead
   of a hash ref, it will assume it is for the "default" pool and will also
   be used as "default_pool". Each destination may be an IP address, a
   single host, or a hostname of a round robin dns to several IP addresses.
   Each destination may be followed by an optional :port to specify which
   port to connect to. The default is http (port 80) if none is specified.

    Example: pools => {
       www => "web.server.com",
       dev => "dev.server.com",
     }

    Example: pools => "web.server.com"

 default_pool

   Specify which key in the pools hash ref should be used if no specific
   pool could be determined based on the request information. If only one
   pool is specified in the pools hash, that pool is assumed to be the
   default_pool.

    Example: default_pool => www

 host_switch_table

   Specify which hosts go to which pools.

    Example: host_switch_table => {
       "server.com" => "www",
       "test.com" => "dev",
     }

 switch_filters

   Supply special header modifications or provide ability to compute
   destination pool based on arbitrary code. It takes an array ref of
   destination pairs. The first in the pair is either a regex or a code
   ref. The second of the pair is the destination pool name from the pools
   setting. If a regex is used, the pool is determined if the regex passes
   when filtered through the header request block. If a code ref is used,
   $_ will contain the request header block. If executing the code ref
   returns a true value, its corresponding pool with be used. This is meant
   to be thought of as a hash ref, but the order must be preserved, and
   refs do not work very well as hash keys, so it uses an array ref
   instead. Be aware that any modifications to $_ will also be passed on to
   the destination regardless of whether the code ref returned a true value
   or not. Also, the switch_filters are run before to the
   host_switch_table.

    Example: switch_filters => [
       qr%^Cookie:.*magic%im => "dev",
       sub { s/^(Host: )www\.%$1%im; 0; } => "dev",
     ]

 connect_timeout

   Specify the maximum number of seconds that a destination node can take
   before it will be considered down. The default is 3 seconds.

    Example: connect_timeout => 10

 check_for_dequeue

   Net::DNAT can periodically perform service checks on the destination
   node of each pool. This setting specifies this interval in seconds. To
   disable these checks, set this to 0. The default is 60 seconds.

    Example: check_for_dequeue => 30

PEER SOCKET SPOOF
   This implementation does not actually translate the destination address
   in the packet headers and resend the packet, like true DNAT does. It is
   implemented like a port forwarding proxy. When a client connects, a new
   socket is made to the remote application and the connection is tunnelled
   to/from the client. This causes the peer side of the socket to appear to
   the remote application like it is coming from the Net::DNAT box instead
   of the real client. This peer modification side effect is usually fine
   for testing and developmental purposes, though.

HTTP
   If you do not care about where the hits on your web server are coming
   from, then you do not need to worry about this section. If the remote
   application is the Apache 1.3.x web server, ( see
   http://httpd.apache.org/ ), then the Apache::DNAT module can be used to
   correctly and seemlessly UnDNATify this peer munging described above. If
   mod_perl is enabled for Apache, then add this line to its httpd.conf:

     PerlModule Apache::DNAT
     PerlInitHandler Apache::DNAT

   If you cannot do this, (because it is a web server other than Apache, or
   you do not have mod_perl enabled, or you do not have access to the web
   server, or you just do not want the CPU overhead to fix the peer back to
   normal, or for whatever reason), then it will still function fine. Just
   the server logs will be inaccurate and the CGI programs will run with
   the wrong environment variables pertaining to the peer (i.e.,
   REMOTE_ADDR and REMOTE_PORT).

INSTALL
   See INSTALL document.

EXAMPLES
   See demo/* from the distribution for some working examples.

TODO
     Test suite example using server and client though Net::DNAT.
     Test suite example using client and pool of servers.
     Test suite example using Apache::DNAT.
     Support for HTTP/1.1 protocol conversion to 1.0 protocol and back again.
     Support for HTTP/1.1 KeepAlive timeout and KeepAliveRequests.
     Support for SSL conversion to plain text and back (IO::Multiplex).
     Support for html error pages for internal errors like Server outages.
     Support for error logs.
     Support for access logs.
     Support for CVS protocol.
     Support for FTP protocol.
     Support for OOB channel data correctly.
     Support for DNS protocol.

LAYER
     More information on network layers:

     http://uwsg.iu.edu/usail/network/nfs/network_layers.html

COPYRIGHT
     Copyright (C) 2002-2003,
     Rob Brown, [email protected]

     This package may be distributed under the same terms as Perl itself.

     All rights reserved.

SEE ALSO
    L<Apache::DNAT>,
    L<Net::Server>,
    L<IO::Multiplex>

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