Configuring Apache HTTP Reverse-Proxy

Exposing OpenKM directly from Tomcat can be risky if you need the application to be accessed from the Internet (for example https://issues.jboss.org/browse/JBAS-3861). It could be infected by PerlBot. Port 8080 may be blocked by a firewall; for this reason, it is recommended to expose your OpenKM installation through the standard web port 80. In the following steps we explain how to configure Apache to handle these requests and forward them to the Tomcat application server using the AJP13 protocol.

From the Apache documentation: The AJP13 protocol is packet-oriented. A binary format was presumably chosen over the more readable plain text for performance reasons. The web server communicates with the servlet container over TCP connections. To cut down on the expensive process of socket creation, the web server will attempt to maintain persistent TCP connections to the servlet container, and to reuse a connection for multiple request/response cycles.

Internal IP vs external IP

Your OpenKM can be accessed from two different zones: Internet and LAN. This means that to access this server you need to use two IPs: external IP (Internet) and internal IP (LAN).

The internal IP address (also known as “local IP address”) is the address that is assigned by your local network router, which often begins with 192.168.x.x. These IP addresses can only be seen by other computers in your local network (LAN) and not by any computers connected in an external network such as the Internet.

To reach the Internet or a computer in another network your computer is often assigned an external IP address, which can then be used to refer to the computer in your local network.

In the above picture, there are three computers in the local network that have each been assigned their own internal IP address by the router. The ISP is connected to the router and gives the router an external IP address that allows it to communicate with the Internet. On the Internet everyone sees your external IP address, but any information coming from the router is “converted” from the external IP address to the internal IP address.

So if you want your OpenKM installation accessible from both LAN and the Internet, the trick here is to configure the client computers to resolve your internal IP (192.168.0.50) if they are inside the LAN or the external IP if they are on the Internet. To resolve the Internet IP (67.166.214.148) your computer uses the public DNS. So, you need to configure a DNS server inside the LAN or modify every client’s hosts file to resolve to the internal IP.

Debian and Ubuntu

The first step is to install the required Apache software. On Debian/Ubuntu you can install Apache with a single command:

$ sudo apt-get install apache2

Edit the file named /etc/apache2/apache2.conf and configure a ServerName to prevent warnings in the Apache startup process:

$ vim /etc/apache2/apache2.conf

ServerRoot "/etc/apache2"
ServerName "localhost"

Note

Editing apache2.conf is optional but sometimes necessary because of the default server name.

Enable the proxy module:

$ sudo a2enmod proxy_ajp
$ sudo a2enmod proxy_wstunnel

Caution

To get WebSocket working you also need Tomcat 8.5.95 or later. Note that the proxy_wstunnel module requires Apache 2.4.5 or later. Please refer to Apache module documentation.

Create the configuration file /etc/apache2/sites-available/openkm.conf with this content:

$ vim /etc/apache2/sites-available/openkm.conf

<VirtualHost *:80>
  ServerName openkm.your-domain.com
  RedirectMatch ^/$ /openkm  # WebSocket support - needs proxy-wstunnel
  ProxyPass /openkm/webSocket ws://127.0.0.1:8080/openkm/webSocket
  ProxyPassReverse /openkm/webSocket ws://127.0.0.1:8080/openkm/webSocket
  ProxyPass /openkm ajp://127.0.0.1:8009/openkm keepalive=On
  ProxyPassReverse /openkm http://openkm.your-domain.com/openkm
  ErrorLog /var/log/apache2/openkm-error.log
  CustomLog /var/log/apache2/openkm-access.log combined
</VirtualHost>

Note

Change openkm.your-domain.com to your server IP or your domain.

The VirtualHost ServerName must be different from the ServerName in the main Apache configuration. Enable this site configuration:

$ cd /etc/apache2/sites-available/
$ sudo a2ensite openkm.conf

You have to explicitly enable proxy access by editing the Apache configuration file /etc/apache2/mods-available/proxy.conf:

$ vim /etc/apache2/mods-available/proxy.conf

<IfModule mod_proxy.c>
  #turning ProxyRequests on and allowing proxying from all may allow
  #spammers to use your proxy to send email.

  ProxyRequests Off

  <Proxy *>
    AddDefaultCharset off
    Order deny,allow
    Allow from all
    Deny from all
    #Allow from .example.com
  </Proxy>

  # Enable/disable the handling of HTTP/1.1 "Via:" headers.
  # ("Full" adds the server version; "Block" removes all outgoing Via: headers)
  # Set to one of: Off | On | Full | Block

  ProxyVia On
</IfModule>

Tip

For security reasons, you might be interested in removing the default Apache configuration:

$ a2dissite 000-default.conf

Check the configuration

Restart Apache:

$ sudo /etc/init.d/apache2 restart

Check access to your OpenKM installation at http://openkm.your-domain.com/.

Tip

Another advantage of using Apache is that you can log OpenKM access and generate web statistics.

Note

To check the configuration files, execute the command:

/usr/sbin/apache2 -t

Red Hat and CentOS

Use the yum application manager to install Apache:

$ sudo yum install httpd

Enable it at boot:

$ sudo chkconfig httpd --level 2345 on

Now create the file /etc/httpd/conf.d/openkm.conf with this content:

$ vim /etc/httpd/conf.d/openkm.conf

<VirtualHost *:80>
  ServerName openkm.your-domain.com
  RedirectMatch ^/$ /openkm  # WebSocket support  ProxyPass /openkm/webSocket ws://127.0.0.1:8080/openkm/webSocket  ProxyPassReverse /openkm/webSocket ws://127.0.0.1:8080/openkm/webSocket  ProxyPass /openkm ajp://127.0.0.1:8009/openkm keepalive=On  ProxyPassReverse /openkm http://openkm.your-domain.com/openkm
  ErrorLog /var/log/httpd/openkm-error.log
  CustomLog /var/log/httpd/openkm-access.log combined
</VirtualHost>

Note

Change openkm.your-domain.com to your server IP or your domain.

Check the configuration

Restart Apache:

$ sudo /etc/init.d/httpd restart

If this command fails, try with:

$ sudo systemctl restart httpd

Check access to your OpenKM installation at http://openkm.your-domain.com/.

Tip

Another advantage of using Apache is that you can log OpenKM access and generate web statistics.

Error Permission denied: proxy: AJP: attempt to connect

If an error like Permission denied: proxy: AJP: attempt to connect appears in the log, solve it by executing the following command:

$ /usr/sbin/setsebool httpd_can_network_connect 1

If it works, then make the configuration permanent to persist across reboots:

$ /usr/sbin/setsebool -P httpd_can_network_connect 1

Troubleshooting

If you see an error message like:

Danger

Invalid command ‘RewriteEngine’, perhaps misspelled or defined by a module not included in the server configuration

You need to enable these Apache modules:

$ sudo a2enmod rewrite
$ sudo a2enmod proxy_http
$ sudo a2enmod headers

If you see errors like these:

[proxy_ajp:error] [pid 27579:tid 140057021224704] (70007)The timeout specified has expired: AH01030: ajp_ilink_receive() can't receive header
[proxy_ajp:error] [pid 27579:tid 140057021224704] [client xxx.xxx.xxx.xxx:60526] AH00992: ajp_read_header: ajp_ilink_receive failed
[proxy_ajp:error] [pid 27579:tid 140057021224704] (70007)The timeout specified has expired: [client xxx.xxx.xxx.xxx:60526] AH00878: read response failed from 127.0.0.1:8009 (127.0.0.1)

It is possible that Tomcat is not accepting AJP connections. Please uncomment these lines in $TOMCAT_HOME/conf/server.xml

<!-- Define an AJP 1.3 Connector on port 8009 -->
<Connector protocol="AJP/1.3" address="127.0.0.1"
           port="8009" redirectPort="8443" secretRequired="false" />

The secretRequired parameter is important, and if it’s not present you need to add it.

More info at Apache Tomcat 8 Configuration Reference.

Additional information

• Apache Module mod_proxy
• Apache Module mod_proxy_ajp
• Apache Module mod_rewrite
• mod_rewrite, a beginner’s guide
• Using Apache Virtual Hosts and ProxyPass Together