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Chapter 12

Administering Multi-Server Applications

This chapter describes how to administer applications on multiple Netscape Application Server (NAS) machines using NAS Administrator.

The following topics are included in this chapter:

Netscape Application Server (NAS) Administrator allows you to simultaneously administer applications that are stored on multiple servers. Settings made to application components, such as Enterprise Java Beans (EJBs), distributed across multiple application servers are automatically updated across those servers. In addition, settings made to one NAS machine can be copied and applied to the other NAS machines in a group or the entire enterprise.

Using the administrator tool, you can view each NAS machine in the enterprise and make changes to one or more servers at the same time.

To host applications on multiple Netscape Application Server (NAS) machines, you can perform either of the following tasks:

The more servers you have to work with, the greater your choice of application hosting configurations.

The following table describes three common ways to host an application on multiple NAS machines:

Hosting configuration
Description
Local
The application is installed on each NAS machine and uses multiple web servers to traffic requests to each server. The NAS machines do not communicate with each other.
Partitioned
Parts of the application are hosted on different NAS machines. Each server knows where the application components of the application are hosted on other servers and forwards requests to the appropriate server.
Distributed for load balancing
Parts or all of the application are duplicated on two or more NAS machines. You can then configure the servers to balance application-request loads.


Hosting Applications Locally on Multiple Servers
Hosting applications locally on multiple servers is the simplest of the three most common server configurations. In this configuration, you deploy the complete application on each NAS machine. If the application is already installed on a NAS machine, you can use the Deployment Manager to deploy the application to other servers.

Supporting applications locally on multiple servers means that each server stands alone. That is, the two or more NAS machines in the configuration do not communicate with each other. You must have at least one web server for each NAS machine. The following illustration depicts a local hosting configuration

Local hosting requires that you configure each web connector plug-in to forward requests to the appropriate NAS machine.


Hosting Partitioned Applications on Multiple Servers
To partition an application, you must divide up the application components that make up an application. Application components are then hosted by separate NAS machines. Partitioning applications allows you to specialize the type of processing each NAS machine is performing.

For example, servlets responsible primarily for data access are I/O-intensive, while servlets responsible for performing calculations are CPU and active-memory intensive. To maximize your application's overall performance, you can partition the application to host these different types of servlets on separate NAS machines.

To configure a partitioned application, perform the following steps:

  1. Deploy the complete application to all participating NAS machines using the Deployment Manager.

  2. Enable load balancing, which will allow each server to find application components hosted on other servers.

  3. Disable specific application components on a server-by-server basis, leaving no component enabled on more than one server.
Alternately, if you want to allow load balancing for specific application components, you can leave them enabled on more than one server.

To partition an application, perform the following steps:

  1. Launch the Deployment Manager.

  2. Deploy the JAR files containing the application components you want to load balance to each application server participating in load balancing.

  3. Open the Application window of NAS Administrator.

  4. In the left pane of the Application window, click the server whose application components you want to partition.

    1. Select an application component in the right pane of the Application window.

    2. Click the Application Component Properties button.

    1. Click OK to dismiss the dialog box.

  5. Click Apply Changes for each NAS machine to which you make changes.
Disabling and Enabling Application Components Disabling a component of your application (such as a servlet) stops users from accessing that component. Current requests are allowed to finish when a component is disabled, but no new requests are accepted until the component is reenabled.

To disable an application component, perform the following steps:

  1. On the NAS Administrator toolbar, click the Application button to open the Application window.

  2. In the left pane of the Application window, double-click the server where the application to be upgraded resides.

  3. Select the folder containing the application components to disable.

    4.

  4. In the right pane of the Application window, select the component to disable.

  5. Click the Enabled checkbox to deselect and disable it.

  6. Repeat steps 2 through 5 for each application component you want to disable.

  7. Click Toggle Enabled if you want to disable all the application components in a group.

  8. Click Apply Changes to save your changes to your NAS machine.

Hosting and Deploying Applications for Load Balancing
Balancing application-request loads, or load balancing, differs from partitioning applications. Load balancing requires you to place one or more copies of an application component on multiple NAS machines rather than simply dividing an application's components among multiple servers (or partitioning the application). You then configure each server, allowing it to find application components on other servers.

When you deploy an application, you must decide if you want to configure the application for load balancing and, if so, how you will configure it. Choose among the following load balancing configurations:

Select the configuration that is most useful for your current scenario; for example, you might have three NAS machines used for testing applications. Your production environment, where users' requests are actually processed, also consists of three NAS machines. Because the application components could be different between the two groups of servers, you do not want to enable application load balancing. Therefore, when you deploy an application from the test servers to the production servers, you should choose only to balance the loads between the destination servers.

Later, should you scale the enterprise to include three more NAS machines in the production group, you can join all the servers in that group when deploying the applications from one of the existing production servers to the new servers. The application loads are then balanced between the existing servers and the new servers.

The following illustration depicts a load-balancing distribution among the destination servers only:

The next illustration depicts a joining of servers when adding new servers to a group and deploying an application to those servers with the join option.

If you choose a local distribution during deployment, no application-request load balancing occurs between any of the servers.


Changing Attributes of Distributed Application Components
When you change such attributes as enabled sticky load balancing for an application component that is distributed across multiple servers, those changes replicate themselves on the servers where that component is hosted. Changing the distribution level of installed application components is useful if you previously installed an application locally, but now want to distribute the application for load balancing. You can also disable load balancing by changing a distributed application to a local configuration on the specified server.

If you change a component from a distributed state to a local state on one server, each server that hosts that component ceases to balance loads with the server where the distribution was set to local.

For example, an application component called ShopCart is distributed across servers A, B, and C. Should you decide to run ShopCart locally on server A, but continue to allow it to run in a distributed state across servers B and C, each server (A, B, and C) is automatically updated so that requests for ShopCart are no longer passed to server A from servers B and C. Instead, requests for ShopCart made to servers B or C are passed only between those two servers. All requests for ShopCart made to server A are processed only by server A.

To change the distribution level for an application component, perform the following steps:

  1. Open the Application window of NAS Administrator.

  2. In the left pane of the Application window, double-click the server for which you want to change application settings.

  3. Select the group of application components you want to modify.

    4.

  4. In the right pane of the Application window, select each application component for which you want to change the distribution level.

  5. In the Mode column, change the distribution level.

  6. In the left pane, under Registered Servers, choose which NAS machines will participate in load balancing of the selected application component. The application component must be installed on each NAS machine participating in load balancing.

  7. If you need to register additional application servers, go to the File menu and choose New, then choose Server.

  8. Repeat these steps for each application component.

  9. Click Apply Changes to save your changes to the NAS machine.
 

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