When do you need a Web application server instead of a Web server?

By Michael Machado
Network World, 4/13/98

Standard Web servers such as Apache, Netscape Communication Corp. Enterprise Server and Microsoft Corp. Internet Information Server provide support for Web applications with simple database access, custom scripting, common gateway interface (CGI) and plug-in extension capabilities.

But mission-critical enterprise Web application development and operation requirements go far beyond these basic features. To support high-end needs, a Web application server has to have built-in redundancy, monitors for high-availability, high-performance distributed application services and support for complex database access.

High availability typically involves providing failover support and automated restart. Netscape Application Server ensures high availability through the use of system monitors, or watchdog processes that start the server's processes and perform regular heartbeat monitoring. When the monitors detect lockups or crashes in a server process, they eliminate the offending process from the available server pool and direct incoming requests to other processes on the same machine or on other servers. System monitors can send warning messages to administrators when processes go down and can automatically restart servers.

To ensure good performance, Netscape Application Server uses dynamic load balancing, which involves spreading incoming requests across a pool of available servers. The product also keeps session information for clients synchronized across the load-balanced pool, allowing Web applications to keep track of session information such as current shopping cart contents even when mulitple servers are involved in handling a transaction.

A Web application server uses caching to speed up system response time to frequently accessed information and resources. Many database interfaces have long connect times, so caching both the connections and frequently requested results can dramatically improve performance. Netscape Application Server can deliver fresh results when needed and cached results when possible.

Most standard Web servers allow you to substitute data into HTML templates via simple data reference tags. Netscape Application Server provides the simple template data reference mechanisms usually found in standard Web servers, but also the ability to reference hierarchical result sets such as products grouped by category and manufacturer.