<?xml version="1.0" encoding="UTF-8"?>
<chapter xml:id="proxying-guacamole" xmlns="http://docbook.org/ns/docbook" version="5.0"
    xml:lang="en" xmlns:xl="http://www.w3.org/1999/xlink" xmlns:xi="http://www.w3.org/2001/XInclude">
    <title>Proxying Guacamole</title>
    <para>Like most web applications, Guacamole can be placed behind a reverse proxy. For production
        deployments of Guacamole, this is <emphasis>highly recommended</emphasis>. It provides
        flexibility and, if your proxy is properly configured for SSL, encryption.</para>
    <para>Proxying isolates privileged operations within native applications that can safely drop
        those privileges when no longer needed, using Java only for unprivileged tasks. On Linux and
        UNIX systems, a process must be running with root privileges to listen on any port under
        1024, including the standard HTTP and HTTPS ports (80 and 443 respectively). If the servlet
        container instead listens on a higher port, such as the default port 8080, it can run as a
        reduced-privilege user, allowing the reverse proxy to bear the burden of root privileges. As
        a native application, the reverse proxy can make system calls to safely drop root privileges
        once the port is open; a Java application like Tomcat cannot do this.</para>
    <section xml:id="preparing-servlet-container">
        <title>Preparing your servlet container</title>
        <para>Your servlet container is most likely already configured to listen for HTTP
            connections on port 8080 as this is the default. If this is the case, and you can
            already access Guacamole over port 8080 from a web browser, you need not make any
            further changes to its configuration.</para>
        <para>If you <emphasis>have</emphasis> changed this, perhaps with the intent of proxying
            Guacamole over AJP, <emphasis>change it back</emphasis>. Using Guacamole over AJP is
            unsupported as it is known to cause problems, namely:</para>
        <orderedlist>
            <listitem>
                <para>WebSocket will not work over AJP, forcing Guacamole to fallback to HTTP,
                    possibly resulting in reduced performance.</para>
            </listitem>
            <listitem>
                <para>Apache 2.4.3 and older does not support the HTTP PATCH method over AJP,
                    preventing the Guacamole management interface from functioning properly.</para>
            </listitem>
        </orderedlist>
        <para>The connector entry within <filename>conf/server.xml</filename> should look like
            this:</para>
        <informalexample>
            <programlisting>&lt;Connector port="8080" protocol="HTTP/1.1" 
           connectionTimeout="20000"
           URIEncoding="UTF-8"
           redirectPort="8443" /></programlisting>
        </informalexample>
        <para>Be sure to specify the <code>URIEncoding="UTF-8"</code> attribute as above to ensure
            that connection names, user names, etc. are properly received by the web application. If
            you will be creating connections that have Cyrillic, Chinese, Japanese, or other
            non-Latin characters in their names or parameter values, this attribute is
            required.</para>
        <section xml:id="tomcat-remote-ip">
            <title>Setting up the Remote IP Valve</title>
            <para>By default, when Tomcat is behind a reverse proxy, the remote IP address of the
                client that it sees is that of the proxy rather than the original client.  In order
                to allow applications hosted within Tomcat, like Guacamole, to see the actual IP
                address of the client, you have to configure both the reverse proxy and Tomcat.</para>
            <para>Because the remote IP address in Guacamole is used for auditing of user logins and
                connections and could potentially be used for authentication, it is important that you
                are either in direct control of the proxy server or you explicitly trust it.  Passing
                the remote IP address is done using the <code>X-Forwarded-For</code> header, and,
                as with most HTTP headers, attackers can attempt to spoof this header in order to
                manipulate the behavior of the web server, gain unauthorized access to the system,
                or attempt to disguise the host or IP address they are coming from.</para>
            <para>One final caveat: This may not work as expected if there are other upstream proxy
                servers between your reverse proxy and the clients access Guacamole.  Other proxies
                or firewalls can mask the IP address of the client, and if the configuration of
                those is not within your control you may end up with multiple clients appearing to
                come from the same IP address or host.  Make sure you take this into account when
                configuring the system and looking at the data provided.</para>
            <para>Configuring Tomcat to pass through the remote IP address provided by the reverse
                proxy in the <code>X-Forwarded-For</code> header requires the configuration of what
                Tomcat calls a Valve.  In this case, it is the <link
                    xl:href="https://tomcat.apache.org/tomcat-8.5-doc/config/valve.html#Remote_IP_Valve">
                    <code>RemoteIpValve</code></link> and is configured in the
                <filename>conf/server.xml</filename> file, in the <code>&lt;Host></code> section:
            </para>
            <informalexample>
                <programlisting>&lt;Valve className="org.apache.catalina.valves.RemoteIpValve"
               internalProxies="127.0.0.1"
               remoteIpHeader="x-forwarded-for"
               remoteIpProxiesHeader="x-forwarded-by"
               protocolHeader="x-forwarded-proto" /></programlisting>
            </informalexample>
            <para>The <parameter>internalProxies</parameter> value should be set to the IP address
                or addresses of any and all reverse proxy servers that will be accessing this Tomcat
                instance directly.  Often it is run on the same system that runs Tomcat, but in other
                cases (for example, when running Docker), it may be on a different system/container and
                may need to be set to the actual IP address of the reverse proxy system.  Only proxy
                servers listed in the <parameter>internalProxies</parameter> or
                <parameter>trustedProxies</parameter> parameters will be allowed to manipulate the
                remote IP address information.  The other parameters in this configuration line allow
                you to control which headers coming from the proxy server(s) are used for various
                remote host information.  They are as follows:
            </para>
            <informaltable frame="all">
                <tgroup cols="2">
                    <colspec colname="c1" colnum="1" colwidth="1*"/>
                    <colspec colname="c2" colnum="2" colwidth="3.55*"/>
                    <thead>
                        <row>
                            <entry>Parameter name</entry>
                            <entry>Description</entry>
                        </row>
                    </thead>
                    <tbody>
                        <row>
                            <entry><parameter>remoteIpHeader</parameter></entry>
                            <entry>
                                <para>The header that is queried to learn the client IP address
                                    of the client that originated the request.  The standard
                                    value is <code>X-Forwarded-For</code>, but can
                                    be configured to any header you like.  The IP address in this
                                    header will be available to Java applications in the
                                    <code>request.getRemoteAddr()</code> method.</para>
                            </entry>
                        </row>
                        <row>
                            <entry><parameter>remoteIpProxiesHeader</parameter></entry>
                            <entry>
                                <para>The header that is queried to learn the IP address of the
                                    proxy server that forwarded the request.  The default value
                                    is <code>X-Forwarded-By</code>, but can be configured to
                                    any header that fits your environment.  This value will only
                                    be allowed by the valve if the proxy used is listed in the
                                    <parameter>trustedProxies</parameter> parameter.  Otherwise
                                    this header will not be available.</para>
                            </entry>
                        </row>
                        <row>
                            <entry><parameter>protocolHeader</parameter></entry>
                            <entry>
                                <para>The header that is queried to determine the protocol
                                    that the client used to connect to the service.  The default
                                    value is <code>X-Forwarded-Proto</code>, but can be
                                    configured to fit your environment.</para>
                            </entry>
                        </row>
                    </tbody>
                </tgroup>
            </informaltable>
            <para>In addition to configuring Tomcat to properly handle these headers, you also may
                need to configure your reverse proxy appropriately to send the headers.  You can
                find instructions for this in <xref linkend="nginx"/> - the Apache web server
                passes it through by default.</para>
        </section>
    </section>
    <section xml:id="nginx">
        <title>Nginx</title>
        <para>Nginx can be used as a reverse proxy, and supports WebSocket out-of-the-box <link
                xl:href="http://nginx.com/blog/websocket-nginx/">since version 1.3</link>. Both
            Apache and Nginx require some additional configuration for proxying of WebSocket to work
            properly.</para>
        <section xml:id="proxying-with-nginx">
            <title>Proxying Guacamole</title>
            <para>Nginx does support WebSocket for proxying, but requires that the "Connection" and
                "Upgrade" HTTP headers are set explicitly due to the nature of the WebSocket
                protocol. From the Nginx documentation:</para>
            <blockquote>
                <para>NGINX supports WebSocket by allowing a tunnel to be set up between a client
                    and a back-end server. For NGINX to send the Upgrade request from the client to
                    the back-end server, Upgrade and Connection headers must be set explicitly.
                    ...</para>
            </blockquote>
            <para>The proxy configuration belongs within a dedicated <link
                    xl:href="http://nginx.org/en/docs/http/ngx_http_core_module.html#location"
                        ><code>location</code></link> block, declaring the backend hosting Guacamole
                and explicitly specifying the "Connection" and "Upgrade" headers mentioned
                earlier:</para>
            <informalexample>
                <programlisting>location /guacamole/ {
    proxy_pass http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/;
    proxy_buffering off;
    proxy_http_version 1.1;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $http_connection;
    access_log off;
}</programlisting>
            </informalexample>
            <para>Here, <replaceable>HOSTNAME</replaceable> is the hostname or IP address of the
                machine hosting your servlet container, and <replaceable>8080</replaceable> is the
                port that servlet container is configured to use. You will need to replace these
                values with the correct values for your server.</para>
            <para>Related to the RemoteIpValve configuration for tomcat, documented in
                <xref linkend="tomcat-remote-ip"/>, the
                <code>proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;</code> line is
                important if you want the <code>X-Forwarded-For</code> header to be passed through
                to the web application server and available to applications running inside it.</para>
            <important>
                <para><emphasis>Do not forget to specify "<code>proxy_buffering
                        off</code>".</emphasis></para>
                <para>Most proxies, including Nginx, will buffer all data sent over the connection,
                    waiting until the connection is closed before sending that data to the client.
                    As Guacamole's HTTP tunnel relies on streaming data to the client over an open
                    connection, excessive buffering will effectively block Guacamole connections,
                    rendering Guacamole useless.</para>
                <para><emphasis>If the option "<code>proxy_buffering off</code>" is not specified,
                        Guacamole may not work</emphasis>.</para>
            </important>
        </section>
        <section xml:id="changing-path-with-nginx">
            <title>Changing the path</title>
            <para>If you wish to serve Guacamole through Nginx under a path other than
                    <uri>/guacamole/</uri>, the configuration will need to be altered slightly to
                take cookies into account. Although Guacamole does not rely on receipt of cookies in
                general, cookies are required for the proper operation of the HTTP tunnel. If the
                HTTP tunnel is used, and cookies cannot be set, users may be unexpectedly denied
                access to their connections.</para>
            <para>Regardless of the location specified for the proxy, cookies set by Guacamole will
                be set using its own absolute path within the backend (<uri>/guacamole/</uri>). If
                this path differs from that used by Nginx, the path in the cookie needs to be
                modified using <code>proxy_cookie_path</code>:</para>
            <informalexample>
                <programlisting>location /<replaceable>new-path/</replaceable> {
    proxy_pass http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/;
    proxy_buffering off;
    proxy_http_version 1.1;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection $http_connection;
    <emphasis>proxy_cookie_path /guacamole/ /<replaceable>new-path/</replaceable>;</emphasis>
    access_log off;
}</programlisting>
            </informalexample>
        </section>
    </section>
    <section xml:id="apache">
        <title>Apache and <package>mod_proxy</package></title>
        <para>Apache supports reverse proxy configurations through <link
                xl:href="http://httpd.apache.org/docs/2.4/mod/mod_proxy.html"
                    ><package>mod_proxy</package></link>. Apache 2.4.5 and later also support
            proxying of WebSocket through a sub-module called <link
                xl:href="http://httpd.apache.org/docs/2.4/mod/mod_proxy_wstunnel.html"
                    ><package>mod_proxy_wstunnel</package></link>. Both of these modules will need
            to be enabled for proxying of Guacamole to work properly.</para>
        <para>Lacking <package>mod_proxy_wstunnel</package>, it is still possible to proxy
            Guacamole, but Guacamole will be unable to use WebSocket. It will instead fallback to
            using the HTTP tunnel, resulting in reduced performance.</para>
        <section xml:id="proxying-with-apache">
            <title>Proxying Guacamole</title>
            <para>Configuring Apache to proxy HTTP requests requires using the
                    <parameter>ProxyPass</parameter> and <parameter>ProxyPassReverse</parameter>
                directives, which are provided by the <package>mod_proxy</package> module. These
                directives describe how HTTP traffic should be routed to the web server behind the
                proxy:</para>
            <informalexample>
                <programlisting>&lt;Location /guacamole/>
    Order allow,deny
    Allow from all
    ProxyPass http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/ flushpackets=on
    ProxyPassReverse http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/
&lt;/Location></programlisting>
            </informalexample>
            <para>Here, <replaceable>HOSTNAME</replaceable> is the hostname or IP address of the
                machine hosting your servlet container, and <replaceable>8080</replaceable> is the
                port that servlet container is configured to use. You will need to replace these
                values with the correct values for your server.</para>
            <important>
                <para><emphasis>Do not forget the <option>flushpackets=on</option>
                        option.</emphasis></para>
                <para>Most proxies, including <package>mod_proxy</package>, will buffer all data
                    sent over the connection, waiting until the connection is closed before sending
                    that data to the client. As Guacamole's HTTP tunnel relies on streaming data to
                    the client over an open connection, excessive buffering will effectively block
                    Guacamole connections, rendering Guacamole useless.</para>
                <para><emphasis>If the option <option>flushpackets=on</option> is not specified,
                        Guacamole may not work</emphasis>.</para>
            </important>
        </section>
        <section xml:id="websocket-and-apache">
            <title>Proxying the WebSocket tunnel</title>
            <para>Apache will not automatically proxy WebSocket connections, but you can proxy them
                separately with Apache 2.4.5 and later using <package>mod_proxy_wstunnel</package>.
                After enabling <package>mod_proxy_wstunnel</package> a secondary
                    <code>Location</code> section can be added which explicitly proxies the
                Guacamole WebSocket tunnel, located at
                <uri>/guacamole/websocket-tunnel</uri>:</para>
            <informalexample>
                <programlisting>&lt;Location /guacamole/websocket-tunnel>
    Order allow,deny
    Allow from all
    ProxyPass ws://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/websocket-tunnel
    ProxyPassReverse ws://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/websocket-tunnel
&lt;/Location></programlisting>
            </informalexample>
            <para>Lacking this, Guacamole will still work by using normal HTTP, but network latency
                will be more pronounced with respect to user input, and performance may be
                lower.</para>
            <important>
                <para>The <code>Location</code> section for <uri>/guacamole/websocket-tunnel</uri>
                    must be placed after the <code>Location</code> section for the rest of
                    Guacamole.</para>
                <para>Apache evaluates all Location sections, giving priority to the last section
                    that matches. If the <uri>/guacamole/websocket-tunnel</uri> section comes first,
                    the section for <uri>/guacamole/</uri> will match instead, and WebSocket will
                    not be proxied correctly.</para>
            </important>
        </section>
        <section xml:id="changing-path-with-apache">
            <title>Changing the path</title>
            <para>If you wish to serve Guacamole through Apache under a path other than
                    <uri>/guacamole/</uri>, the configuration required for Apache will be slightly
                different than the examples above due to cookies.</para>
            <para>Guacamole does not rely on receipt of cookies for tracking whether a user is
                logged in, but cookies are required for the proper operation of the HTTP tunnel. If
                the HTTP tunnel is used, and cookies cannot be set, users will be unexpectedly
                denied access to connections they legitimately should have access to.</para>
            <para>Cookies are set using the absolute path of the web application
                    (<uri>/guacamole/</uri>). If this path differs from that used by Apache, the
                path in the cookie needs to be modified using the
                    <parameter>ProxyPassReverseCookiePath</parameter> directive:</para>
            <informalexample>
                <programlisting>&lt;Location /<replaceable>new-path/</replaceable>>
    Order allow,deny
    Allow from all
    ProxyPass http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/ flushpackets=on
    ProxyPassReverse http://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/
    <emphasis>ProxyPassReverseCookiePath /guacamole/ /<replaceable>new-path/</replaceable></emphasis>
&lt;/Location>

&lt;Location /<replaceable>new-path</replaceable>/websocket-tunnel>
    Order allow,deny
    Allow from all
    ProxyPass ws://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/websocket-tunnel
    ProxyPassReverse ws://<replaceable>HOSTNAME</replaceable>:<replaceable>8080</replaceable>/guacamole/websocket-tunnel
&lt;/Location></programlisting>
            </informalexample>
            <para>This directive is not needed for the WebSocket section, as it is not applicable.
                Cookies are only used by Guacamole within the HTTP tunnel.</para>
        </section>
        <section xml:id="disable-tunnel-logging">
            <title>Disabling logging of tunnel requests</title>
            <para>If WebSocket is unavailable, Guacamole will fallback to using an HTTP-based
                tunnel. The Guacamole HTTP tunnel works by transferring a continuous stream of data
                over multiple short-lived streams, each associated with a separate HTTP request. By
                default, Apache will log each of these requests, resulting in a rather bloated
                access log.</para>
            <para>There is little value in a log file filled with identical tunnel requests, so it
                is recommended to explicitly disable logging of those requests. Apache does provide
                a means of matching URL patterns and setting environment variables based on whether
                the URL matches. Logging can then be restricted to requests which lack this
                environment variable:</para>
            <informalexample>
                <programlisting>SetEnvIf Request_URI "^<replaceable>/guacamole</replaceable>/tunnel" dontlog
CustomLog  <replaceable>/var/log/apache2/guac.log</replaceable> common env=!dontlog</programlisting>
            </informalexample>
            <para>Note that if you are serving Guacamole under a path different from
                    <uri>/guacamole/</uri>, you will need to change the value of
                    <parameter>Request_URI</parameter> above accordingly.</para>
        </section>
    </section>
</chapter>