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mod_proxy.html
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mod_proxy.html
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<!DOCTYPE html>
<html>
<head>
<title>ProFTPD module mod_proxy</title>
</head>
<body bgcolor=white>
<hr>
<center>
<h2><b>ProFTPD module <code>mod_proxy</code></b></h2>
</center>
<hr><br>
<p>
The purpose of the <code>mod_proxy</code> module is to provide FTP proxying
capabilities in <code>proftpd</code>, both <em>reverse</em> (or "gateway")
proxying and <em>forward</em> proxying.
<p>
Installation instructions are discussed <a href="#Installation">here</a>.
<b>Note</b> that <code>mod_proxy</code> requires ProFTPD 1.3.6rc2 or later.
Detailed notes on best practices for using this module are
<a href="#Usage">here</a>.
<p>
This product includes software developed by the OpenSSL Project for use in the OpenSSL Toolkit (http://www.openssl.org/).
<p>
This product includes cryptographic software written by Eric Young (eay@cryptsoft.com).
<p>
The most current version of <code>mod_proxy</code> can be found at:
<pre>
<a href="https://github.com/Castaglia/proftpd-mod_proxy.git">https://github.com/Castaglia/proftpd-mod_proxy.git</a>
</pre>
<h2>Author</h2>
<p>
Please contact TJ Saunders <tj <i>at</i> castaglia.org> with any
questions, concerns, or suggestions regarding this module.
<h2>Thanks</h2>
<p>
<i>2015-08-24</i>: Thanks to Michael Toth <mtoth <i>at</i> queldor.net>
for helping test multiple iterations of <code>mod_proxy</code> with IIS
servers.
<h2>Directives</h2>
<ul>
<li><a href="#ProxyDataTransferPolicy">ProxyDataTransferPolicy</a>
<li><a href="#ProxyDatastore">ProxyDatastore</a>
<li><a href="#ProxyDirectoryListPolicy">ProxyDirectoryListPolicy</a>
<li><a href="#ProxyEngine">ProxyEngine</a>
<li><a href="#ProxyForwardEnabled">ProxyForwardEnabled</a>
<li><a href="#ProxyForwardMethod">ProxyForwardMethod</a>
<li><a href="#ProxyForwardTo">ProxyForwardTo</a>
<li><a href="#ProxyLog">ProxyLog</a>
<li><a href="#ProxyOptions">ProxyOptions</a>
<li><a href="#ProxyReverseConnectPolicy">ProxyReverseConnectPolicy</a>
<li><a href="#ProxyReverseServers">ProxyReverseServers</a>
<li><a href="#ProxyRetryCount">ProxyRetryCount</a>
<li><a href="#ProxyRole">ProxyRole</a>
<li><a href="#ProxySFTPCiphers">ProxySFTPCiphers</a>
<li><a href="#ProxySFTPCompression">ProxySFTPCompression</a>
<li><a href="#ProxySFTPDigests">ProxySFTPDigests</a>
<li><a href="#ProxySFTPHostKey">ProxySFTPHostKey</a>
<li><a href="#ProxySFTPKeyExchanges">ProxySFTPKeyExchanges</a>
<li><a href="#ProxySFTPOptions">ProxySFTPOptions</a>
<li><a href="#ProxySFTPPassPhraseProvider">ProxySFTPPassPhraseProvider</a>
<li><a href="#ProxySFTPServerAlive">ProxySFTPServerAlive</a>
<li><a href="#ProxySFTPServerMatch">ProxySFTPServerMatch</a>
<li><a href="#ProxySFTPVerifyServer">ProxySFTPVerifyServer</a>
<li><a href="#ProxySourceAddress">ProxySourceAddress</a>
<li><a href="#ProxyTables">ProxyTables</a>
<li><a href="#ProxyTimeoutConnect">ProxyTimeoutConnect</a>
<li><a href="#ProxyTimeoutLinger">ProxyTimeoutLinger</a>
<li><a href="#ProxyTLSCACertificateFile">ProxyTLSCACertificateFile</a>
<li><a href="#ProxyTLSCACertificatePath">ProxyTLSCACertificatePath</a>
<li><a href="#ProxyTLSCARevocationFile">ProxyTLSCARevocationFile</a>
<li><a href="#ProxyTLSCARevocationPath">ProxyTLSCARevocationPath</a>
<li><a href="#ProxyTLSCertificateFile">ProxyTLSCertificateFile</a>
<li><a href="#ProxyTLSCertificateKeyFile">ProxyTLSCertificateKeyFile</a>
<li><a href="#ProxyTLSCipherSuite">ProxyTLSCipherSuite</a>
<li><a href="#ProxyTLSEngine">ProxyTLSEngine</a>
<li><a href="#ProxyTLSOptions">ProxyTLSOptions</a>
<li><a href="#ProxyTLSPreSharedKey">ProxyTLSPreSharedKey</a>
<li><a href="#ProxyTLSProtocol">ProxyTLSProtocol</a>
<li><a href="#ProxyTLSTimeoutHandshake">ProxyTLSTimeoutHandshake</a>
<li><a href="#ProxyTLSTransferProtectionPolicy">ProxyTLSTransferProtectionPolicy</a>
<li><a href="#ProxyTLSVerifyServer">ProxyTLSVerifyServer</a>
</ul>
<p>
<hr>
<h3><a name="ProxyDataTransferPolicy">ProxyDataTransferPolicy</a></h3>
<strong>Syntax:</strong> ProxyDataTransferPolicy <em>client|active|passive|pasv|epsv|port|eprt</em><br>
<strong>Default:</strong> ProxyDataTransferPolicy client<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyDataTransferPolicy</code> directive configures the data
transfer <em>policy</em> that <code>mod_proxy</code> uses when performing
data transfers (<i>e.g.</i> file uploads/downloads, directory listings) with
the backend/destination server.
<p>
The currently supported policies are:
<ul>
<li><code>client</code>
<p>
This policy indicates that <code>mod_proxy</code> will use whatever
the connected client uses. Thus if the client sends <code>PORT</code>,
<code>mod_proxy</code> will send <code>PORT</code> to the
backend/destination server.
<p>
This is the <em>recommended policy</em> in most cases.
</li>
<p>
<li><code>active</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <em>active</em> data transfers (<i>i.e.</i> using
<code>PORT</code> commands) with the backend/destination server.
</li>
<p>
<li><code>passive</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <em>passive</em> data transfers (<i>i.e.</i> using
<code>PASV</code> commands) with the backend/destination server.
</li>
<p>
<li><code>PASV</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <code>PASV</code> commands with the backend/destination
server.
</li>
<p>
<li><code>PORT</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <code>PORT</code> commands with the backend/destination
server.
</li>
<p>
<li><code>EPSV</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <code>EPSV</code> commands with the backend/destination
server.
</li>
<p>
<li><code>EPRT</code>
<p>
Regardless of the commands sent by the client, <code>mod_proxy</code>
will use only <code>EPRT</code> commands with the backend/destination
server.
</li>
</ul>
<p>
<hr>
<h3><a name="ProxyDatastore">ProxyDatastore</a></h3>
<strong>Syntax:</strong> ProxyDatastore <em>type [info]</em><br>
<strong>Default:</strong> ProxyDatastore SQLite<br>
<strong>Context:</strong> server config<br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyDatastore</code> directive configures the <em>type</em> of
datastore that <code>mod_proxy</code> uses for persistence. The currently
supported datastore <em>types</em> are:
<ul>
<li>Redis
<li>SQLite
</ul>
<p>
<b>Note</b> that the Redis <em>type</em> also requires the <em>info</em>
parameter, namely a prefix for all of the Redis keys. This prefix <b>must</b>
be different/unique among all of your <code>mod_proxy</code> servers using
that Redis server/cluster; the prefix is used to keep all of the data
<i>for this server</i> separate from all other servers. For example:
<pre>
<IfModule mod_proxy.c>
...
<IfModule mod_redis.c>
# Use our IP address as our prefix
ProxyDatastore Redis 1.2.3.4.
</IfModule>
</IfModule>
</pre>
<p>
<hr>
<h3><a name="ProxyDirectoryListPolicy">ProxyDirectoryListPolicy</a></h3>
<strong>Syntax:</strong> ProxyDirectoryListPolicy <em>client|"LIST" [opt1 ...]</em><br>
<strong>Default:</strong> ProxyDirectoryListPolicy client<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyDirectoryListPolicy</code> directive configures the directory
list <em>policy</em> that <code>mod_proxy</code> uses when performing
directory lists with the backend/destination server.
<p>
The currently supported policies are:
<ul>
<li><code>client</code>
<p>
This policy indicates that <code>mod_proxy</code> will use whatever
the connected client uses. Thus if the client sends <code>MLSD</code>,
<code>mod_proxy</code> will send <code>MLSD</code> to the
backend/destination server.
<p>
This is the <em>recommended policy</em> in most cases.
</li>
<p>
<li><code>LIST</code>
<p>
This policy instructs <code>mod_proxy</code> to use the <code>LIST</code>
command with the backend/destination server, regardless of the command
used by the client. The <code>mod_proxy</code> module then handles any
reformatting of the <code>LIST</code> response into the response needed
by the client. For example, if the client sends <code>MLSD</code> but the
backend/destination server does not support this command,
<code>mod_proxy</code> will send <code>LIST</code> instead, and translate
the backend format into the client-requested format.
<p>
The current implementation of this policy handles <code>LIST-<MLSD</code>
translations only.
</li>
</ul>
You may also provide <em>options</em>; the currently implemented
<em>options</em> are:
<ul>
<li><code>UseSlink</code><br>
<p>
Use this option to have <code>mod_proxy</code> use the <i>broken</i>
"OS.unix=slink" syntax, preferred by FTP clients such as FileZilla, for
indicating symlinks, rather than the more correct "OS.unix=symlink"
syntax. See
<a href="http://bugs.proftpd.org/show_bug.cgi?id=3318">Bug#3318</a> for
a more detailed discussion.
</li>
</ul>
<p>
<hr>
<h3><a name="ProxyEngine">ProxyEngine</a></h3>
<strong>Syntax:</strong> ProxyEngine <em>on|off</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyEngine</code> directive toggles the support for proxying by
<code>mod_proxy</code>. This is usually used inside a
<code><VirtualHost></code> section to enable proxying of FTP sessions for
a particular virtual host. By default <code>mod_proxy</code> is disabled for
both the main server and all configured virtual hosts.
<p>
<hr>
<h3><a name="ProxyForwardEnabled">ProxyForwardEnabled</a></h3>
<strong>Syntax:</strong> ProxyForwardEnabled <em>on|off</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> <code><Class></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc2 and later
<p>
The <code>ProxyForwardEnabled</code> directive determines whether a client
can use <code>mod_proxy</code> for forward proxying, based on that client's
<a href="http://www.proftpd.org/docs/howto/Classes.html">class</a>.
<p>
By default, <code>mod_proxy</code> rejects any forward proxy request from
<b>any</b> client, with the exception of clients connecting from
<a href="http://www.faqs.org/rfcs/rfc1918.html">RFC 1918</a> addresses:
<pre>
192.168.0.0/16
172.16.0.0/12
10.0.0.0/8
</pre>
This is done as a security measure: <b>open/unrestricted proxy servers are
dangerous both to your network and to the Internet at large</b>. Thus to make
it possible for clients to use your server for forward proxying, they <b>must
be explicitly</b> enabled to do so.
<p>
Example:
<pre>
<Class forward-proxy>
From 1.2.3.4/12
# Allow clients from this class to use FTP forward proxying
ProxyForwardEnabled on
</Class>
</pre>
<p>
See also: <a href="#ProxyForwardTo"><code>ProxyForwardTo</code></a>
<p>
<hr>
<h3><a name="ProxyForwardMethod">ProxyForwardMethod</a></h3>
<strong>Syntax:</strong> ProxyForwardMethod <em>method</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyForwardMethod</code> directive configures the <em>method</em>
that clients can use for requesting forward proxying. Some methods require
that the client authenticate <em>to the proxy first</em>, and then separately
authenticate to the destination server; these methods differ on just when
the client specifies the destination server. Other methods do not require
proxy authentication. There are many variations on a theme with these methods.
<p>
The currently supported methods are:
<ul>
<li><code>proxyuser,user@host</code>
<p>
This method indicates that proxy authentication is <b>required</b>. The
client first authenticates to the proxy via <code>USER/PASS</code> commands:
<pre>
USER <em>proxy-user</em>
PASS <em>proxy-passwd</em>
</pre>
Then the client authenticates <i>again</i>, this time including the
address (and optionally port) of the destination server as part of the
second <code>USER</code> command:
<pre>
USER <em>real-user</em>@ftp.example.com
PASS <em>real-passwd</em>
</pre>
The <code>mod_proxy</code> module will remove the destination address
portion of the second <code>USER</code> command before proxying it to
the destination server.
</li>
<p>
<li><code>proxyuser@host,user</code>
<p>
This method indicates that proxy authentication is <b>required</b>. The
client first authenticates to the proxy via <code>USER/PASS</code> commands;
note that the destination address (and optionally port) is included as part
of the first <code>USER</code> command:
<pre>
USER <em>proxy-user</em>@ftp.example.com
PASS <em>proxy-passwd</em>
</pre>
Then the client authenticates <i>again</i>, this time sending the
<code>USER/PASS</code> commands to authenticate to the destination server:
<pre>
USER <em>real-user</em>
PASS <em>real-passwd</em>
</pre>
</li>
<p>
<li><code>user@host</code>
<p>
This methods indicates that <i>no proxy authentication</i> is used. The
client indicates the destination address (and optionally port) of the
server as part of the <code>USER</code> command:
<pre>
USER <em>real-user</em>@ftp.example.com
PASS <em>real-passwd</em>
</pre>
The <code>mod_proxy</code> module will remove the destination address
portion of the <code>USER</code> command before proxying it to the
destination server.
</li>
<p>
<li><code>user@sni</code>
<p>
This methods indicates that <i>no proxy authentication</i> is used. The
client indicates the destination address (and optionally port) of the
server as part of a TLS SNI (Server Name Indication) portion of a TLS
session:
<pre>
AUTH TLS <em>handshake with SNI</em>
USER <em>real-user</em>
PASS <em>real-passwd</em>
</pre>
</li>
</ul>
<p>
Configuring the FTP client's proxy settings to match the above methods varies
greatly, depending on the FTP client.
<p>
<hr>
<h3><a name="ProxyForwardTo">ProxyForwardTo</a></h3>
<strong>Syntax:</strong> ProxyForwardTo <em>[!]pattern [flags]</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyForwardTo</code> directive is used to restrict which
hosts/domains can be requested for forward proxying. The destination host/port
for forward proxying <b>must</b> match the configured <em>pattern</em>
regular expression, or the forward proxying request will fail.
<p>
The optional <em>flags</em> parameter, if present, modifies how the given
<em>pattern</em> will be evaludated. The supported flags are:
<ul>
<li><b>nocase|NC</b> (<b>n</b>o <b>c</b>ase)<br>
This makes the <em>pattern</em> case-insensitive, <i>i.e.</i> there is
no difference between 'A-Z' and 'a-z' when <em>pattern</em> is matched
against the path
</li>
</ul>
<p>
<code>ProxyForwardTo</code> limits the destination hosts <b>to</b> which
clients can request forward proxying; by contrast,
<a href="#ProxyForwardEnabled"><code>ProxyForwardEnabled</code></a> controls
forward proxying based on where clients connect <b>from</b>.
<p>
Example:
<pre>
# Limit forward proxying to specific host and port
ProxyForwardTo ^ftp.example.com:21$
</pre>
<p>
<hr>
<h3><a name="ProxyLog">ProxyLog</a></h3>
<strong>Syntax:</strong> ProxyLog <em>path|"none"</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyLog</code> directive is used to specify a log file for
<code>mod_proxy</code>'s reporting on a per-server basis. The <em>path</em>
parameter given must be the full path to the file to use for logging.
<p>
Note that this path must <b>not</b> be to a world-writable directory and,
unless <code>AllowLogSymlinks</code> is explicitly set to <em>on</em>
(generally a bad idea), the path must <b>not</b> be a symbolic link.
<p>
<hr>
<h3><a name="ProxyOptions">ProxyOptions</a></h3>
<strong>Syntax:</strong> ProxyOptions <em>opt1 ...</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyOptions</code> directive is used to configure various optional
behavior of <code>mod_proxy</code>. For example:
<pre>
ProxyOptions UseProxyProtocolV1
</pre>
<p>
The currently implemented options are:
<ul>
<li><code>ShowFeatures</code><br>
<p>
When reverse proxying, <code>mod_proxy</code> defaults to not responding to
the FTP <code>FEAT</code> command, which is used to determine the supported
features/capabilities of the FTP server; this is done to prevent leaking
of information about internal FTP servers to the outside world. However,
some clients rely on the <code>FEAT</code> data. For such clients/use
cases, use this option to tell <code>mod_proxy</code> to proxy the
<code>FEAT</code> command/response to the backend server.
</li>
<p>
<li><code>UseDirectDataTransfers</code><br>
<p>
The <code>mod_proxy</code> module will, by default, proxy all data transfers
through the proxy server. Some sites may wish to have the FTP data
transfers occur directly between the frontend client and the backend server,
to avoid the latency/overhead of the proxying. Use this option to
enable these direct data transfers (akin to <b>D</b>irect <b>S</b>erver
<b>R</b>eturn, or DSR), for both forward and reverse proxy roles:
<pre>
# Enable data transfers directly from frontend client to/from backend server
ProxyOptions UseDirectDataTransfers
</pre>
</li>
<p>
<li><code>UseProxyProtocolV1</code><br>
<p>
When <code>mod_proxy</code> connects to the backend/destination server,
use the <a href="http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt"><code>PROXY</code></a> V1 protocol, sending the human-readable <code>PROXY</code>
command to the destination server. This allows backend servers to implement
access controls/logging, based on the IP address of the connecting client.
The <a href="https://github.com/Castaglia/proftpd-mod_proxy_protocol"><code>mod_proxy_protocol</code></a>
ProFTPD module can be used to handle the <code>PROXY</code> command on
the receiving side, <i>i.e.</i> when using <code>proftpd</code> as the
backend/destination server.
<p>
<b>Note</b>: do <b>not</b> use this option unless the backend server
<em>does</em> support the <code>PROXY</code> V1 protocol. Otherwise, the
<code>PROXY</code> protocol message will only confuse the backend server,
possibly leading to connection/login failures.
</li>
<p>
<li><code>UseProxyProtocolV2</code><br>
<p>
When <code>mod_proxy</code> connects to the backend/destination server,
use the <a href="http://www.haproxy.org/download/1.8/doc/proxy-protocol.txt"><code>PROXY</code></a> V2 protocol, sending a binary-encoded "PROXY" command
to the destination server. This allows backend servers to implement
access controls/logging, based on the IP address of the connecting client.
The <a href="https://github.com/Castaglia/proftpd-mod_proxy_protocol"><code>mod_proxy_protocol</code></a>
ProFTPD module can be used to handle the "PROXY" command on the receiving
side, <i>i.e.</i> when using <code>proftpd</code> as the
backend/destination server.
<p>
<b>Note</b>: do <b>not</b> use this option unless the backend server
<em>does</em> support the <code>PROXY</code> V2 protocol. Otherwise, the
"PROXY" protocol message will only confuse the backend server, possibly
leading to connection/login failures.
</li>
<p>
<li><code>UseProxyProtocolV2TLVs</code><br>
<p>
When <code>mod_proxy</code> is configured to use the PROXY protocol V2,
via the <code>UseProxyProtocolV2</code> option, this option tells
<code>mod_proxy</code> to send additional data as Type/Length/Value (TLV).
These TLVs include:
<ul>
<li>ALPN (Application Layer Protocol Negotiation)
<li>Authority (Hostname provided by client)
<li>SSL/TLS (whether SSL/TLS is in use at the time of the PROXY protocol)
<li>SSL/TLS protocol version
<li>SSL/TLS cipher
<li>Unique ID (when <a href="http://www.proftpd.org/docs/contrib/mod_unique_id.html"><code>mod_unique_id</code></a> is present/used)
</ul>
<p>
<b>Note</b>: use of the <code>UseProxyProtocolV2</code> option is also
required for the TLVs to be sent.
</li>
<p>
<li><code>UseReverseProxyAuth</code><br>
<p>
When reverse proxying, <code>mod_proxy</code> delegates user authentication
to the selected backend server. However, there are some sites which need
to centralize user authentication in the proxy; use this option to require
proxy authentication for such cases. <b>Note</b> that this option
<b>only</b> pertains to reverse proxy connections; proxy authentication
when forward proxying is determined by the <code>ProxyForwardMethod</code>
directive.
</li>
</ul>
<p>
<hr>
<h3><a name="ProxyRetryCount">ProxyRetryCount</a></h3>
<strong>Syntax:</strong> ProxyRetryCount <em>count</em><br>
<strong>Default:</strong> ProxyRetryCount 5<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyRetryCount</code> directive configures the number of times
<code>mod_proxy</code> will attempt to connect to the backend/destination
server. The default is <em>5</em> attempts.
<p>
<hr>
<h3><a name="ProxyReverseConnectPolicy">ProxyReverseConnectPolicy</a></h3>
<strong>Syntax:</strong> ProxyReverseConnectPolicy <em>policy</em><br>
<strong>Default:</strong> RoundRobin<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyReverseConnectPolicy</code> directive configures the
<em>policy</em> that <code>mod_proxy</code> will use for selecting the backend
server when reverse proxying.
<p>
The currently supported policies are:
<ul>
<li><code>LeastConns</code>
<p>
Select the backend server with the lowest number of proxied connections.
</li>
<p>
<li><code>LeastResponseTime</code>
<p>
Select the backend server with the least response time; this is determined
based on the connect time to the backend server, and its number of
current connections.
</li>
<p>
<li><code>PerGroup</code>
<p>
Select a backend server based on the primary group of the authenticated
<code>USER</code> name used by the connecting client; any future
connections using that same <code>USER</code> name will be routed to the
same backend server.
<p>
<b>Note</b>: use of this <code>ProxyReverseConnectPolicy</code> also
<b>requires</b> use of the <code>UseReverseProxyAuth</code>
<code>ProxyOption</code>, as authenticating the given <code>USER</code>
name is required for discovering the primary group of that user.
</li>
<p>
<li><code>PerHost</code>
<p>
Select a backend server based on the IP address of the connecting client;
any future connections from that IP address will be routed to the same
backend server.
</li>
<p>
<li><code>PerUser</code>
<p>
Select a backend server based on the <code>USER</code> name used by the
connecting client; any future connections using that same <code>USER</code>
name will be routed to the same backend server.
</li>
<p>
<li><code>Random</code>
<p>
Randomly select any of the backend servers.
</li>
<p>
<li><code>RoundRobin</code>
<p>
Select the next backend server in the list.
</li>
<p>
<li><code>Shuffle</code>
<p>
Similar to the <code>Random</code> policy, except the selection happens
from the not-yet-chosen backend servers. This means that <b>all</b>
backend servers will eventually be used evenly, just in a random order.
</li>
</ul>
<p>
<hr>
<h3><a name="ProxyReverseServers">ProxyReverseServers</a></h3>
<strong>Syntax:</strong> ProxyReverseServers <em>servers</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyReverseServers</code> directive configures the list of servers
to be used as the backend servers for reverse proxying.
<p>
Each server <b>must</b> be configured as a <i>URL</i>. Only the "ftp" and
"ftps" schemes are currently supported. If not specified, the port will be
21. IPv6 addresses <b>must</b> be enclosed within square brackets. Thus, for
example, the following are all valid URLs:
<pre>
ftp://<em>ftp1.example.com:2121</em>
ftp://<em>1.2.3.4</em>
ftp://<em>[::ffff:6.7.8.9]:2121</em>
ftps://<em>ftp2.example.com</em>
ftps://<em>ftp3.example.com:990</em>
</pre>
And using them all in the configuration would look like:
<pre>
ProxyReverseServers ftp://ftp1.example.com:2121 ftps://1.2.3.4 ftp://[::ffff:6.7.8.9]:2121
</pre>
<p>
The backend servers can also be discovered via DNS <code>SRV</code> or <code>TXT</code> records, using <code>SRV/TXT</code> URL scheme variants, <i>e.g.</i>:
<pre>
# Discover backend addresses via DNS SRV records
ftp+srv://_ftp._tcp.castaglia.org
# Discover backend addresses via DNS TXT records (which must be an FTP URL)
ftp+txt://castaglia.org
</pre>
These <code>SRV/TXT</code> URL scheme variations also apply to FTPS URLs.
<b>Note</b> that any explicit port numbers provided in URLs using these
<code>SRV/TXT</code> scheme variants <i>will be ignored</i>; the actual port
numbers to use will be discovered from the <code>SRV</code> and <code>TXT</code>
DNS records.
<p>
The backend servers can <i>also</i> be contained in a list in a JSON file,
<i>e.g.</i>:
<pre>
[
"ftp://ftp1.example.com:2121",
"ftp://[::ffff:6.7.8.9]:2121"
]
</pre>
You then only need to configure the path to that JSON file:
<pre>
ProxyReverseServers file:/path/to/backends.json
</pre>
<p>
<b>Note</b> that <code>mod_proxy</code> has strict requirements for the
permissions on <code>ProxyReverseServers</code> files. The configured file
<em>must not be world-writable</em>, since that would allow <i>any user</i>
on the system to modify the file, directing proxied connections anywhere else.
If a world-writable <code>ProxyReverseServers</code> file is found, you will
see the following error message logged:
<pre>
unable to use world-writable ProxyReverseServers '/opt/proxy/reverse.json' (perms 0666): Operation not permitted
</pre>
In addition, the <i>directory</i> containing the
<code>ProxyReverseServers</code> file cannot be world-writable, either. Even
if the file itself is not world-writable, being in a world-writable directory
means that <i>any user</i> on the system can delete that file, and write a new
file. When a world-writable directory is found, the following error is logged:
<pre>
unable to use ProxyReverseServers '/opt/proxy/reverse.json' from world-writable directory '/opt/proxy' (perms 0777): Operation not permitted
</pre>
<p>
The backend servers can <i>also</i> be provided from an external SQL database,
queried by <code>mod_proxy</code> via <a href="http://www.proftpd.org/docs/contrib/mod_sql.html#SQLNamedQuery"><code>SQLNamedQuery</code></a>. For example,
<i>assuming</i> a schema such as this:
<pre>
CREATE TABLE proxy_user_servers (
user_name TEXT,
url TEXT
);
CREATE INDEX proxy_user_servers_name_idx ON proxy_user_servers (user_name);
</pre>
where <em>url</em> contains URLs, <i>e.g.</i> "ftp://1.2.3.4:21". Then you
would configure <code>mod_proxy</code> to query for those per-user backend URLs
using <code>ProxyReverseServers</code> like this:
<pre>
<IfModule mod_sql.c>
...
SQLNamedQuery get-user-servers SELECT "url FROM proxy_user_servers WHERE user_name = %{0}"
</IfModule>
ProxyRole reverse
ProxyReverseConnectPolicy PerUser
ProxyReverseServers sql:/get-user-servers
</pre>
<p>
Given that <code>mod_proxy</code> uses SQLite, does that mean that the table
used for storing these per-user URLs <b>must</b> be SQLite? <b>No</b>. The
use of <code>SQLNamedQuery</code> means that <b>any database</b>, supported
by <code>mod_sql</code>, can be used.
<p>
<hr>
<h3><a name="ProxyRole">ProxyRole</a></h3>
<strong>Syntax:</strong> ProxyRole <em>role</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.6rc1 and later
<p>
The <code>ProxyRole</code> directive configures whether <code>mod_proxy</code>
will perform forward or reverse proxying. The list of supported <em>roles</em>
are thus:
<ul>
<li><code>forward</code>
<p>
Perform forward proxying.
</li>
<p>
<li><code>reverse</code>
<p>
Perform reverse proxying.
</li>
</ul>
<p>
<b>Note</b> that the <code>ProxyRole</code> directive is <b>required</b>
for <code>mod_proxy</code> to function. If this directive is not configured,
connections to <code>mod_proxy</code> will fail.
<p>
<hr>
<h3><a name="ProxySFTPCiphers">ProxySFTPCiphers</a></h3>
<strong>Syntax:</strong> ProxySFTPCiphers <em>algo1 ...</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.8rc3 and later
<p>
The <code>ProxySFTPCiphers</code> directive is used to specify the list of
cipher algorithms that <code>mod_proxy</code> should use when connecting to
backend SSH servers. The current list of supported cipher algorithms is, in
the default order of preference:
<ul>
<li>aes256-ctr
<li>aes192-ctr
<li>aes128-ctr
<li>aes256-gcm@openssh.com
<li>aes128-gcm@openssh.com
<li>aes256-cbc
<li>aes192-cbc
<li>aes128-cbc
<li>cast128-cbc
<li>3des-ctr
<li>3des-cbc
</ul>
By default, all of the above cipher algorithms are presented to the server,
in the above order, during the key exchange.
<p>
The "none" cipher (<i>i.e.</i> no encryption) will <b>not</b> be presented to
the server by default; any sites which wish to use "none" will have to
explicitly configure it via <code>ProxySFTPCiphers</code>.
<p>
Note that CTR mode ciphers (<i>e.g.</i> the <code>aes128-ctr</code>,
<code>aes192-ctr</code>, and <code>aes256-ctr</code> ciphers) are recommended.
Any CBC mode cipher allows for the possibility of an attack which causes
several bits of plaintext to be leaked; the attack is described
<a href="http://www.cpni.gov.uk/Docs/Vulnerability_Advisory_SSH.txt">here</a>.
This attack is on the SSH2 protocol design itself; any SSH2 implementation
which conforms to the RFCs will have this weakness.
<p>
In general, there is no need to use this directive unless only one specific
cipher must be used.
<p>
<hr>
<h3><a name="ProxySFTPCompression">ProxySFTPCompression</a></h3>
<strong>Syntax:</strong> ProxySFTPCompression <em>on|off|delayed</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.8rc3 and later
<p>
The <code>ProxySFTPCompression</code> directive enables the use of zlib
compression of the payload of SSH2 packets. This can make for smaller packets,
but require more CPU time to compress/uncompress the data.
<p>
The <em>delayed</em> parameter tells <code>mod_proxy</code> to support a custom
extension used by OpenSSH, where compression is not actually enabled until
after the client has successfully authenticated.
<p>
<hr>
<h3><a name="ProxySFTPDigests">ProxySFTPDigests</a></h3>
<strong>Syntax:</strong> ProxySFTPDigests <em>algo1 ...</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.8rc3 and later
<p>
The <code>ProxySFTPDigests</code> directive is used to specify the list of
MAC digest algorithms that <code>mod_proxy</code> should use when connecting to
backend SSH servers. The current list of supported MAC algorithms is:
<ul>
<li>hmac-sha2-256
<li>hmac-sha2-256-etm@openssh.com
<li>hmac-sha2-512
<li>hmac-sha2-512-etm@openssh.com
<li>hmac-sha1
<li>hmac-sha1-etm@openssh.com
<li>hmac-sha1-96
<li>hmac-sha1-96-etm@openssh.com
<li>umac-64@openssh.com
<li>umac-64-etm@openssh.com
<li>umac-128@openssh.com
<li>umac-128-etm@openssh.com
</ul>
By default, all of the above MAC algorithms are presented to the server,
in the above order, during the key exchange. <b>Note</b> that some algorithms
(<i>e.g.</i> the SHA256 and SHA512 algorithms) may not be supported by
the version of OpenSSL used; this will be automatically detected.
<p>
The following list of algorithms are <em>supported</em>, but <b>not</b>
presented to servers by default. These algorithms must be <em>explicitly</em>
configured via <code>ProxySFTPDigests</code> to be available for use by servers:
<ul>
<li>hmac-md5
<li>hmac-md5-etm@openssh.com
<li>hmac-md5-96
<li>hmac-md5-96-etm@openssh.com
<li>hmac-ripemd160
</ul>
<p>
The "none" MAC (<i>i.e.</i> no MAC) will <b>not</b> be presented to the server
by default; any sites which wish to use "none" will have to explicitly
configure it via <code>ProxySFTPDigests</code>.
<p>
In general, there is no need to use this directive unless only one specific
MAC algorithm must be used.
<p>
<hr>
<h3><a name="ProxySFTPHostKey">ProxySFTPHostKey</a></h3>
<strong>Syntax:</strong> ProxySFTPHostKey <em>file</em>|agent:<em>/path</em><br>
<strong>Default:</strong> None<br>
<strong>Context:</strong> server config, <code><VirtualHost></code>, <code><Global></code><br>
<strong>Module:</strong> mod_proxy<br>
<strong>Compatibility:</strong> 1.3.8rc3 and later
<p>
The <code>ProxySFTPHostKey</code> directive configures the path to a host key
file. The <code>mod_proxy</code> module uses the keys thus configured for
"hostbased" user authentication to backend SSH servers.
<p>
You can use either an RSA key, a DSA key, and/or ECDSA keys. These <i>could</i>
be the exact same host key files as used by your SSH server, <i>e.g.</i>:
<pre>
<IfModule mod_sftp.c>
...
SFTPHostKey /etc/ssh_host_dsa_key
SFTPHostKey /etc/ssh_host_rsa_key
SFTPHostKey /etc/ssh_host_ecdsa_key
SFTPHostKey /etc/ssh_host_ed25519_key
</IfModule>
<IfModule mod_proxy.c>
ProxyEngine on
..
ProxySFTPHostKey /etc/ssh_host_dsa_key
ProxySFTPHostKey /etc/ssh_host_rsa_key
ProxySFTPHostKey /etc/ssh_host_ecdsa_key
ProxySFTPHostKey /etc/ssh_host_ed25519_key
</IfModule>
</pre>
<p>
The <code>ProxySFTPHostKey</code> directive can also be used to load host keys
from an SSH agent such as OpenSSH's <code>ssh-agent</code>. For example:
<pre>
# Load all of the keys from the ssh-agent configured for proxy use
ProxySFTPHostKey agent:%{env:SSH_AUTH_SOCK}
</pre>
Using an SSH agent for storing host keys allows for configurations where
the host keys are not stored on files on the server system, <i>e.g.</i>
the keys can be loaded into the SSH agent from a PKCS#11 token.
<p>
<hr>
<h3><a name="ProxySFTPKeyExchanges">ProxySFTPKeyExchanges</a></h3>
<strong>Syntax:</strong> ProxySFTPKeyExchanges <em>algo1 ...</em><br>