UPDATE: Not applicable to LiveRebel version 2.x and later
It’s been a busy summer so far with LiveRebel – previously we looked at LiveRebel’s command line interface (CLI), something we hope more people learn about, and scripting Java EE hot updates using LiveRebel and Bash. You may have already checked out our LiveRebel Amazon AMI for really quick LiveRebel testing, and we’ve whipped up a really tasty Chef LiveRebel Recipe, a single-command LiveRebel installation.
I’ve spent some time recently getting funky with GlassFish clusters using LiveRebel, our recently-released Java-Hot-Update-Done-Right tool that allows you to do fully automated hot updates to a running application without downtime.
Most recently, we added support for GlassFish application servers, so I figured it was about time to show how LiveRebel could be used to roll updates to an application that runs in a Glassfish cluster. In this post we show how to configure a basic GlassFish cluster and how to connect the nodes to LiveRebel and run hot updates for your application.
Configuring a Glassfish cluster
We will be using a GlassFish Server 3.1 Open Source Edition Full Platform version, which is available from java.net. After downloading and extracting the archive we have everything ready to start our first GlassFish instance. We are going to create a cluster that consists of two instances, running on the same node. To do that, we need to follow a procedure described in a tutorial video by an Oracle employee. Later, we will change the configuration of our cluster, but for now, it is sufficient. To create a cluster using the GlassFish web-console, follow these steps.
glassfish3/glassfish/asadmin start-domain --verbose.
- Navigate to localhost:4848 and log into GlassFish console.
- Click Cluster menu item,
New...specify cluster name (we will use RebelCluster) and create two new server instances. It is important to select Make a Copy of the Selected Configuration, because later we will change that and we don’t want to change the default configuration file.
- Start the cluster using the start cluster button.
Now we can check if the cluster is alive. Select menu Clusters->ClusterName in the GlassFish web-console, choose the Instances tab. Both instances should have Running status.
Cool. We have a healthy cluster of GlassFish servers up. Now we can proceed with deploying an application there.
Deploying an Application to Your GlassFish cluster
We need to perform an initial deploy of the application. Before we deploy an application, we need to supply it with a
liverebel.xml file which serves as a marker for LiveRebel that this application can be managed by LiveRebel.
If you manage your application with maven, you don’t even need to write this file by hand — see how to generate this with maven automatically.
If you do not manage your application with maven,
liverebel.xml is a small file that specifies the application name and its version. Here we will use RebelChat demo application, the
liverebel.xml file for version 1.0, which looks like this:
<?xml version="1.0" encoding="UTF-8"?> <application> <name>RebelChat</name> <version>1.0</version> </application>
liverebel.xml file should be put into
WEB-INF/classes directory of your WAR. If you want to run your tests with prepackaged WAR files, then consider using our rebel-chat demo versions:
Now we have an application ready to be deployed. Select the Applications tab in your cluster menu. Click the
Deploy... button, specify the path to the WAR file, context path and application name. Also, make sure that Selected Targets where you deploy this application contains your cluster. In our case, it looks like this:
OK and in a few seconds your application is deployed. We can check it by navigating to:
Port values 28080 and 28081 are defaults, where GlassFish cluster instances serve http requests. You can check if these are correct by exploring your cluster Instances tab and clicking on the instance name. You are interested in the middle of the HTTP ports, i.e. 28081 in the following image:
Note that in a real-life situation, you will have a load balancer in front of the GlassFish cluster, so there will be no need to specify ports or jump from one port to another if we want to check both servers. But for our purposes, it is enough. Now go and check that RebelChat is indeed deployed.
We can see that despite the fact that RebelChat application doesn’t use all the features offered by clustering, both instances in RebelCluster are running the chat.
Now it’s time to get the LiveRebel Command Center running and investigate what features it offers you.
Configuring LiveRebel Command Center
It’s time to set up the LiveRebel Command Center web-console, which we will use later to modify GlassFish cluster configurations.
Now you need to download the LiveRebel archive if you haven’t already. We are currently providing everyone with a three-month evaluation license, which is more than enough for the purposes of this, and all the other, LiveRebel How-tos. Unzip the archive and you will see the following directory layout:
Start the LiveRebel Command Center by running
lr-command-center.cmd on Windows) script from the
bin folder. The initial configuration of the LiveRebel Command Center includes registration of LiveRebel (as a product) and user profile creation. Rest assured, both processes are trivial form submissions and are described in the LiveRebel walkthrough. By now, you should have the LiveRebel Command Center running and configured. Next, it’s time to configure your servers and applications.
Click on the Add Server button, and download
lr-agent.jar to some location. This jar is a –
javaagent file that can be attached to an application server and managed from the LiveRebel Command Center. To attach it to GlassFish instances that form our cluster, we need to modify their configuration.
Go back to the GlassFish web-console, open Configurations » YourClusterName-config menu. This item was created when we specified it to copy the default configuration at cluster creation time. We need to add two JVM options, so open the JVM settings menu item, then JVM Options tab. Using the Add JVM Option button, add the following options:
-javaagent will tell GlassFish, where to find LiveRebel agent and
-Xverify:none allows us to make the necessary bytecode operations for updating application versions.
Save this configuration change. Notice how the GlassFish web-console notifies us, that we need to restart cluster instances. Stop and start these instances using the buttons on GlassFish web-console.
Now we go back to the LiveRebel Command Center and see that LiveRebel took up – you can see that the RebelChat application deployed on two servers.
Next, we show how to update an application version from the LiveRebel Command Center.
Updating an Application with LiveRebel
Updating clustered application with LiveRebel is done in the same manner as for a usual application. This process is described in detail in LiveRebel Installation and configuration walkthrough. But we also briefly describe it here.
When you open the LiveRebel Command Center, you see a list of all the applications managed by LiveRebel. Currently, we see that RebelChat is deployed on two servers. Click on the application name, which is RebelChat at the moment.
Click the Upload new version button and proceed with uploading
rebel-chat-1.1.war. LiveRebel takes us back to the Show all deployments screen. Here, we select both servers, as we want to update the application in both of them, and click Prepare Update.
We proceed with checking compatibility between currently deployed 1.0 version of RebelChat and version 1.1, to which we want to update. Expectedly, these versions are compatible with warnings, which means that we can proceed with update.
Click Proceed with update and Update buttons, as we are quite happy with default configuration for current update. LiveRebel Command Center sends series of commands to both GlassFish servers and shows us a short log of what has been done.
As we see Version updated successfully, we go to the browser, where chats are open to check that.
Yay! Both chats are updated. Both preserved previous states. And it is equally easy to revert the application to version 1.0 from LiveRebel Command Center or to proceed with updating to a version 1.2.
This wraps up a guide about how to configure a GlassFish cluster to work with LiveRebel. Happy updating!