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Chapter 11

Configuring Multiple Servers

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

The following topics are included in this chapter:


The Web Connector in a Multiple-Server Enterprise
The web connector plug-in directs users' requests to applications on your Netscape Application Server (NAS) machine. In a multiple-server enterprise, you can specify the application server where the web connector connects and logs web server requests. The application server you specify is the default server where the web connector exchanges requests and other application information. When the load balancer plug-in does not specify an alternate application server where application requests are forwarded, application requests are sent to this default server.

You can also specify the application server where the web connector sends the application request information for logging.

Configuring the Web Connector for Multiple Servers When you use multiple NAS machines to support your enterprise application or applications, you must choose how to configure the web server to forward requests to NAS. These configuration options are provided by the web connector plug-in. Use the configuration scenarios described in the following table to help you decide how best to configure the web connector plug-in for your enterprise:

Configuration scenarios
What to do
One web server supporting multiple NAS machines without load balancing
It is assumed that the application is partitioned. Configure the web plug-in to forward requests to the application server that hosts the application objects that process the initial requests from the web browser. Use the other NAS machines to host the application components invoked by the objects on the first server.
Multiple web servers supporting multiple NAS machines without load balancing
If the application is not partitioned, configure each plug-in to forward requests to each appropriate NAS machine.
If the application is partitioned, configure each plug-in to forward requests to a NAS machine that hosts the components that process the initial web browser requests. You can have multiple plug-ins connect to a single NAS machine.
One web server supporting multiple NAS machines with load balancing
The load balancing plug-in forwards application requests to the appropriate NAS machine.
As a default, configure the web connector plug-in to forward requests to a NAS machine that either performs the best or hosts the application components that process the initial web browser requests.
Multiple web servers supporting multiple NAS machines with load balancing
The load balancing plug-in forwards application requests to the appropriate NAS machine.
As a default, configure the web connector plug-ins to forward requests to each NAS machine, or to the NAS machine that either performs the best or hosts the application components that process the initial web browser requests.

When you balance application loads, the web connector plug-in works with the load balancer plug-in to automatically distribute requests across multiple NAS machines. This prevents all requests from going to one NAS machine.

If you are not balancing application loads, you must determine where a web server forwards application requests.

Specifying the Application Server Where Requests Are Sent In a multiple application server enterprise, you can specify where the web connector sends application requests.

If you have enabled load balancing, the load balancer plug-in first dictates where the request is forwarded. However, if you have not configured the load balancer plug-in to decide where to send the request, the web connector forwards the request to the NAS machine you specify.

To specify the NAS machine to which the web server connects, perform the following steps:

  1. Open the Netscape Registry Editor by typing kregedit at the command line.

  2. Open the following key:

  3. Double-click the GXIP String value.

  4. For the value data, enter the host IP address for the default NAS machine and click OK.
Specifying the Application Server Responsible for Logging In a multiple-server enterprise, you can specify the application server used for web server logging.

In a single-server enterprise, the single server is the NAS machine where the web connector forwards application requests by default. For single-server enterprises, this value should not be changed.

In a multiple-server enterprise, the logging application server is the same server where the web connector sends application requests by default.

To specify the NAS machine responsible for logging, perform the following steps:

  1. Open the Netscape Registry Editor by typing kregedit at the command line.

  2. Open the following key:

  3. Double-click the Host String value.

  4. For the value data, enter the host IP address for the application server you want to perform web server logging and click OK.

  5. Double-click the Port DWORD value.

  6. For the value data, enter the port number for the Executive Server process of the same application server and click OK.

  7. Close the editor tool.

Distributed Data Synchronization and Load Balancing
When you create a multiple application server enterprise, you must know if you want to enable load balancing across those servers. Applications that are distributed for load balancing might have dependencies on the distributed sychronization service of the application server if those applications require state and session management.

Distributed data synchronization is configured when you install Netscape Application Server (NAS). The installation script asks whether the server will participate in distributed data synchronization, as well as the host name and port number of the primary server. For more information about distributed data synchronization, see About Distributed Data Synchronization.

Configuring a Distributed Data Synchronization Environment Once you install NAS on multiple machines, you must update the cluster keys of the servers participating in distributed data synchronization. This is done using the Netscape Registry Editor.

Updating the keys of servers in a cluster ensures that each server has the same information about the primary server, the immediate backups, and the priority in which other servers might become a primary server in the event of a server failure.

To configure a distributed data synchronization environment, see Managing Distributed Data Synchronization.


Multicast Communication
In a multiple-server enterprise, application servers communicate with each other, for purposes of load balancing and administration, using a multicast wide area network (WAN) service. The multicast service provides a virtual server to which all messages can be posted and distributed. The application servers use an N-Way multicast configuration that allows each server to send or receive the broadcast information. The following illustration shows how this network looks:

Multicast services are handled by the network hardware for all servers within a local area network (LAN). For these servers, you do not have to register or change the default multicast address. When you are implementing an enterprise in a wide area network, you should use a publicly registered multicast address that allows only your NAS machines to communicate with each other.

How Multicast Services Apply to Load Balancing For load balancing, you can have all servers communicate with each other, or you can create islands of servers that only balance application loads between themselves. For example, an application in New York does not need to load balance with the same application in Los Angeles. However, an application in Cupertino, Sunnyvale, and Santa Clara probably would share load responsibilities for all the users in the San Jose area.

For load balancing, multicast communication is determined by the Executive Server multicast address.

 

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