December 11, 2006

Core and Render Services

While implementing software systems you have two different major issues.
  • Implementing Core Functions: Can be considered as commit transactions( Insert records, transfer files to legacy systems, batch imports) . These methods are atomic and can change the entire data for the whole system.
  • Rendering data as Human Readable Form. All Forms, lists, Reports can be considered in this case. There is no data change in background system but only export of this system.
When you distinguish these two system you can separate the implementation of these functionality. CoreService,RenderService.

  • CoreService: have transactional service methods. Each method is a atomic unit and as a whole the services capture whole system functions.So they are reusable
  • RenderService: Can be implemented depending on the domain. Either Web Technologies, reporting or desktop applications. Each domain have its own constraints so unlike CoreService these methods are hardly reusable.
Here is sample Dependency Diagram.

Sample Flow would be like:
  1. User request page with a GET method
  2. Render Service render the html and form.
  3. User fills the forms and POST the data
  4. Core method reads the data from request and commit the transaction
  5. Redirect the request to and URL
  6. Another GET and render Case

With this pattern you support and increase the separation of concern and increase the abstraction layer.

For java web applications, it would be best to use a action oriented framework like Struts suits well for the pattern

November 12, 2006

Load Balance and Cluster Setup for Tomcat via Apache 2.2

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Hello, here I will try to describe a sample configuration of a multiple tomcats and one APACHE for load balancing and identical tomcat server instances. These tomcat instances will be identical since they serve the same application 'medya'. This sample is based on opensuse 10.1 Remastered with apache 2.2 and tomcat 5.5.20. It’s done for a server with 16GB RAM and 4 CPUs and jvm only enable 2 GB heap size

main purpose is using same tomcat-home for diffrent tomcat-bases for identically same tomcat instances

Part I: Tomcat Cluster and Linux Service definitions

First download and extract the tomcat 5.5.x to /usr/tomcat55 this will the unique tomcat home for our tomcat instances. Same tomcat instance count will be 3 (s1,s2,s3). Then replace server.xml with the same file at the attachment. This file contains simple variable configuration like

<Server port="${tomcat.server.port}1" shutdown="SHUTDOWN"> .... <Connector port="${tomcat.server.port}2 ...

variable are given as external jvm parameters for the same configuration file.

tomcat.base: standard tomcat variable for common base jars files names and shell scripts.
tomcat.server.port: used in the configuration file as port prefix
${tomcat.server.port}1: Shutdown port
${tomcat.server.port}2: http connector port
${tomcat.server.port}3: ajp connector

eg:if tomcat.server.port:771 then shutdown port will be 7711, http will be 7712,ajp will be 7713 tomcat server name for load balancing and cluster

and sample tomcat cluster configuration

then create a directory for first tomcat base. /opt/tb55/s1 and link file system to base tomcat instance I do this sample on a single computer and it can be done over a network since the files are only used at startup for very limit size. and copy same base for more

mkdir /opt/tb55
mkdir /opt/tb55/s1
ln /usr/tomcat55/conf /opt/tb55/s1/conf -s
ln /usr/tomcat55/shared /opt/tb55s1/shared -s
mkdir /opt/tb55/s1/logs
mkdir /opt/tb55/s1/temp
cp /usr/tomcat55/webapps /opt/tb55/s1/webapps -R
cp /opt/tb55/s1 /opt/tb55/s2 -R
cp /opt/tb55/s1 /opt/tb55/s3 -R

Up to we build single tomcat home and three tomcat base. these instances have same library with different applcation base(webapps),log and temp directories.

Part II: Defining and starting tomcats as linux service in a cluster structure.

copy the to /usr/tomcat55/bin it will be standard startup script. this script is based upon the script at link. and copy startup script tb-s1,tb-s2,tb-s3 to /etc/init.d for service definition.

content of tb-s1 (tomcat 1 service script)

export CATALINA_PORT=`echo $PP`1
export CATALINA_HOME=/usr/tomcat55
export JAVA_OPTS="-Duser.language=en -Dtomcat.server.port=$PP$CATALINA_NAME"
export JAVA_HOME=/usr/java/jdk1.5.0_05
su $TOMCAT_USER -m -c "/usr/tomcat55/bin/ $1"

As you see this contains variables for server.xml and jvm options you add or remove yours. this service will be run as a system user tomcat.

now you can add this service as system service

chkconfig --add tb-s1
chkconfig --add tb-s2
chkconfig --add tb-s3

Part III: Defining AJP connector ,proxy and load balancer for APACHE

put mod_proxy_balancer.conf to /etc/apache2/conf.d

this file contains all configuration for

proxy_ajp_module: for tomcat ajp connector used by proxy module

proxy_module: used by apache to support for proxy
proxy_balancer_module: used to load balance application context over different tomcat instances

LoadModule proxy_module /usr/lib/apache2/
LoadModule proxy_balancer_module /usr/lib/apache2/
LoadModule proxy_ajp_module /usr/lib/apache2/
<Location /balancer-manager>
SetHandler balancer-manager
<Proxy balancer://medyaCluster>
BalancerMember ajp://localhost:7713 route=s1
BalancerMember ajp://localhost:7723 route=s2
BalancerMember ajp://localhost:7733 route=s3
<Location /medya>
ProxyPass balancer://medyaCluster/medya stickysession=JSESSIONID

and restart apache2 service

Part IV: Deploying Sample application

simple put you application folder to /home/tomcat/medya

and out medya.xml to /usr/tomcat55/conf/Catalina/localhost/medya.xml

<Context docBase="${user.home}/medya" distributable="true" path="/medya"></Context>

I hope you enjoy your application :) .

Sorry for formating :(


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