About Rama Krishnan

Ramki is a Application Developer working in the C-DAC, Pune. He has Extensive Design and Development experience in Java, Java Server Faces, Servlets, Java Persistent API (Hibernate), CDI, EJB and experience in applying Design Patterns of JavaEE Architecture.

Virtual Host + Apache httpd server + Tomcat + mod_jk connector

In my last post (Virtual Host in Tomcat) we discussed about how setup the virtual host in Tomcat. Its cost effective technique because only one public IP is enough to host multiple domain. If we have big organization and each department want to host their website in locally in different machine. then how to achieve the virtual host concept?. In this post we will see the how we do this.

Problem Scenario: In big organization they have multiple department, each department want to host their website in different machine. so these websites are accessed locally with different local IP address.

When we mapping to public address then we face the problem. We have two choice either purchase as many public address or Put one server front and delegate these request.

We going to use 2nd option. we put Apache httpd web server in front of all department servers. so only one public IP is enough. All domain DNS entries are pointed to Apache httpd server. Then Apache server delegates these request to corresponding tomcat server. This process is completely transparent from users(browser) perspective.

Outline Structure of Virtual Host Implementation

How Apache httpd web server communicate to Tomcat server

Before we going to detail about how communication happen between httpd server and tomcat

How many ports are bind when we start single tomcat?

  • shutdown port 
  • http connector port 
  • https connector port (optional) 
  • ajp port

The port configuration are stored in $CATALINA_HOME/conf/server.xml file. we can change the ports when its necessary.

Here AJP (Apache JServ Protocol) is a binary protocol that can proxy inbound requests from a web server through to an application server that sits behind the web server.

Apache httpd webserver communicate to Tomcat sever through AJP protocol.

When we install Apache httpd server, It doesn’t have inbuilt capability to support ajp protocol. so we need mod_jk module. Its add the ajp support to Apache httpd server.

Steps to Implement Virtual Host Concept in this Scenario:

  1. Install Apache httpd Web Server 
  2. Install mod_jk connector 
  3. Configure JK Connector 
  4. Configure Apache httpd server, apply virtual host concepts

Prerequisite: We already installed Tomcat in different departments and deployed the application and works fine.

Install Apache httpd web server

We can install Apache web server in two ways:

  1. Binary module
  2. From Source

We can install Apache httpd server from distribution package manager (either apt-get or yum). Or we can download the source code and then compile and install.

We use the second option. First download the httpd server source code from here . then extract it and install

./configure --prefix=/usr/local/apache    --enable-rewrite=shared  --enable-proxy=shared
make
sudo make install

Here –prefix option to mention where the location we going to install Apache httpd server. –enable-rewrite and –enable-proxy options to enable these module in shared mode. These modules are not needed now. but we used in future for rewrite the URL before handover to next chain of servers and load-balancing support.

Install mod_jk connector

Now Apache httpd server is ready. we need to add ajp support to server. download the mod_jk connector module from here, extract it and install it

cd native
./configure    --with-apxs=/usr/local/apache/bin/apxs

make
sudo make install

Here –with-apxs option to specify where apxs module is located. so we need to give Apache httpd server location. Now mod_jk.so files is created on modules directory in apache installed location (/usr/local/apache/modules)

Configure mod_jk connector

This step have 2 sub step:

  1. Create workers.properties file 
  2. Load and configure the JK connector module in apache httpd.conf file 

Create workers.properties file

mod_jk connector is ready. but this connector is works based on configuration file. so we need to create configuration file called workers.properties file

This file syntax is key=value pair, here we define the workers. i.e all department tomcat hosts IP address and ajp port for corressponding tomcat.

Here entry format is look like:

worker.<name>.property=<value>

For example:

worker.<name>.type=ajp13
worker.<name>.port=<ajp port>
worker.<name>.host=<tomcat ip addr>
worker.list=<name>

Here:

  • worker.list key have all workers name separated by comma
  • type = here type of the worker. we use ajp13 version 
  • port= we specify the ajp port (not http port ) of that server
  • host= IP address or host name of tomcat server

workers.properties

worker.list=department1,department2,department3

worker.department1.type=ajp13
worker.department1.port=5000
worker.department1.host=192.168.5.10

worker.department2.type=ajp13
worker.department2.port=5000
worker.department2.host=192.168.6.10

worker.department3.type=ajp13
worker.department3.port=5000
worker.department3.host=192.168.7.10

Add Entry in httpd.conf

Apache httpd server is installed. mod_jk module is installed and workers.properties file is created. but these 3 are isolated. we put together,we need to configure the httpd server.

Find the conf/httpd.conf file in Apache installed location and add these following entries to it

LoadModule    jk_module  modules/mod_jk.so

JkWorkersFile conf/workers.properties

JkLogFile     logs/mod_jk.log
JkLogLevel    emerg
JkLogStampFormat "[%a %b %d %H:%M:%S %Y] "
JkOptions     +ForwardKeySize +ForwardURICompat -ForwardDirectories
JkRequestLogFormat     "%w %V %T"

Here:

  • LoadModule – Load mod_jk shared module to Apache httpd server (enable the mod_jk module) 
  • JkWorkersFile – Specify the workers.properties file location 
  • all others are logging system of mod_jk. Its boilerplate code just copy and paste.

Delegate httpd to Tomcat

Now we inform to Apache httpd server how delegate the request to corresponding server.

JkMount  /department1* department1
JkMount  /department2* department2
JkMount  /department3* department3

Here:

  • JkMount – specify the if URL have /department1* pattern then that request delegate to department1 
  • worker. that worker IP address and port is specified in workers.properties file.

We changed /etc/hosts file like last post all web site domain pointed to apache httpd web server.

If we access http://www.ramki.com/department1/index.html how Apache httpd server process the request

Its perfectly called correct tomcat server and we got right response.

But we have 2 problems
1.I don’t want the my URL like this http://www.ramki.com/department1/index.html
i want the my URL like this http://www.ramki.com/index.html

Remove the department1 from my URL. but department1 string is very important in URL because JkMount is works based on this matching string only.

2. http://www.ramki.com/department1/index.html is for first tomcat and second department have domain http://www.krishnan.com then access second tomcat we use URL : http://www.krishnan.com/department2/index.html but same time when we use URL http://www.krishnan.com/department1/index.html then we access first tomcat data
(i.e )
http://www.ramki.com/department1/index.html == http://www.krishnan.com/department1/index.html because both these URL have department1 key word.. so JkMount is works based on these keyword. As the Result wrong interpretation. How to solve this Issue?.

Virtual Host in Apache httpd Server

We need add conditional JkMount. for example ramki.com domain asks the whereare paths like department1,department2 we need to search in that tomcat only. not other place. to add this conditioned we add virtual host entries.

Add virtual host entry in httpd.conf file

Listen 80
NameVirtualHost *:80

<VirtualHost *:80>
    ServerName www.ramki.com
    JkMount  /department1* department1
</VirtualHost>

<VirtualHost *:80>
    ServerName www.krishnan.com
    JkMount  /department2* department1
</VirtualHost>

Here
ServerName – domain name of the server

If http://www.krishnan.com/department1/index.html URL is like this now. server matches the Server Name. here its matches 2nd virtual host entry. There are single JkMount entry is there in 2nd Virtual-Host. and there no matching department1 string.

JkMount  /department2* department1

As the result 404 error page is responded. Its works good.

Now everythig works fine. Now my URL is http://www.ramki.com/department1/index.html here i don’t want department1 path in my URL. I want simply http://www.ramki.com/index.html then we use mod_rewrite engine

Listen 80
NameVirtualHost *:80

<VirtualHost *:80>
     ServerName www.ramki.com
     RewriteEngine on 
     RewriteLog logs/apache-mod_rewrite
     RewriteRule ^/(.*)$ /department1/$1 [L,PT]
     JkMount  /* <dept_name>
</VirtualHost>

Here:

  • RewriteEngine on – Turn on the Rewrite module 
  • RewriteRule ^/(.*)$ /department1/$1 [L,PT] – here ^/(.*)$ its matches any string it capture the value to $1 and change the URL to /department1/$1

i.e

http://www.ramki.com/index.html here ^/(.*)$ its matches index.html it capture to $1 and replaced to /department1/$1 ==> /department1/index.html

Rewrite happens before delegate the request to Tomcat. so we change the URL transparently to browser. Now client (browser) just send http://www.ramki.com is enough to access the Department 1 Tomcat.

Sreen Cast

Reference: Virtual Host + Apache httpd server + Tomcat + mod_jk connector from our JCG partner Rama Krishnan at the Ramki Java Blog blog.

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