Simple Sample

This is a Sample Java Application for OpenShift JBoss cartridges, that is used to demonstrate some of the OpenShift basics.

This uses the OpenShift jbosseap cartridge. Documentation on the cartridge can be found at: https://github.com/openshift/origin-server/tree/master/cartridges/openshift-origin-cartridge-jbosseap/README.md

To use this set of examles create a Java Application following the online examples or with:

rhc create-app -a jbossexamples -t jbosseap-6

Following this you can pull in the code from these examples by using:

git remote add examples https://github.com/gssOpenShiftsupportExamples/JavaSample.git
git fetch examples
git checkout master; git merge --strategy=recursive -X theirs examples/master
git push

• Note: Then change in the merge strategy is so you can avoid conflicts.

You can then navigate to http://APP_NAME-NAMESPACE.rhcloud.com/example/ to see this samle in action.

What this example demonstrates

The objectives of this example are fairly simple, and are designed as a starting point for most new developers or individuals who are simply new to OpenShift.

• Demonstrate how to create an Application (shown above)
• Demonstrate how to pull in code from an exsisting repository with git remotes (shown above)
• Demonstrate how to push code to your gear and do a maven build (explained below; shown above)
• Demonstrate how to change the version of Java that the container used (explained in the war)
• Demonstrate how to deploy a binary artificat (explained in the war)

Of the item that are not already covered (above) this example contains a simple servelet that is maped to ExampleServlet when the examle.war is deployed. This servelet is simply used demonstrate the basics to creating custom java code and how to place that with in a WAR. This example (if you use the links provided) can also show you how to wire up servelet maps so that HTTP request made to the container can be serviced by the servelet.

The example.war can be build from scratch using maven and the openshift profile. The reason this is demonstrated in this manner is so that you can see the differenc between an example build from source vs an example deployed as a binary (thus demonstrating 2 of the above objectives).

For more information on this see the deployed war at: http://APP_NAME-NAMESPACE.rhcloud.com/example/ as it explains how to continue this example and deploy a binary artifact.

To see what maven will do when you push the code to the gear (or to simply test code modifications localy) simply run (the following) at the root of your git repository. It will simulate what happens on a git push or what happens when a build is done.

mvn -e clean package -Popenshift -DskipTests

The maven command (as demonstraged above) simply builds the java code (the example servelet and bundles up the other resources) to create the example.war file. It then places this war file into the deployments direcory of your git repository on the gear, completing the build.

• Note: The built war file is not checked-in or commited to the git repository.

In addition to providing you with a simple build and demonstraing how the WAR maps to the Sample Servlet this example also provide you a demonstration on how the WAR can be marked as a clustered application.

When an application is marked in this way the container can be clustered with other containers to handle more request or provide fail over functionality.

To see this in action you would want to create a clustered JBoss application:

rhc create-app -a jbossexamples -t jbosseap-6 -s

By default OpenShift scales applicatoins based on load (so unless you are generating a large amount of load you will need to disable this feature and manualy scale your application).

You can Disable Auto Scaling by completing the following in your git repo:

touch .openshift/markers/disable_auto_scaling  
git add .openshift/markers/disable_auto_scaling  
git commit -m "Disabling Auto Scaling, Switching to Manual Scaling"  
git push  

You can then Manually Scale your GEAR by running the following commands:

rhc ssh APPNAME  
rhc cartridge scale jbosseap-6 -a APP_NAME NUMBER_OF_GEARS

Once you have scaled your app you can see how many gears are active by running the following:

rhc app show $APP_NAME --gears | tail -3

You can also see what GEAR you get serviced by (by looking at the Servlet). Simply look at the IP value on the Clustered Servlet: http://app_name-namespace-rhcloud.com/example/ExampleServlet

To kill the JBoss Server that serviced your request you can run (be sure to fill in the APP_NAME and IP place holders:

IP="xxx.xxx.xxx"; APP_NAME="NAME"; for x in $(rhc app show $APP_NAME --gears | tail -3 | awk '{print $7}'); do ssh $x "if [[ $IP == \$OPENSHIFT_JBOSSEAP_IP ]]; then pkill java;fi;"; done;

By simply refresshing the Clustered Servlet: http://app_name-namespace-rhcloud.com/example/ExampleServlet you can see that the SessionID stays the same but the IP changes to one of your other JBoss gears. This demonstrates that the refreshed request was serviced by another JBoss sever hower the content of your session was maintain.