Whatever their purpose, such server-side programs generate a response, most often in HTML, for viewing in a Web browser.
Understand that a Web server’s delegation model is fairly simple. When a request comes into the Web server, the Web server simply passes the request to the program best able to handle it.
The Web server doesn’t provide any functionality beyond simply providing an environment in which the server-side program can execute and pass back the generated responses. The server-side program usually provides for itself such functions as transaction processing, database connectivity, and messaging.
While a Web server may not itself support transactions or database connection pooling, it may employ various strategies for fault tolerance and scalability such as load balancing, caching, and clustering features oftentimes erroneously assigned as features reserved only for application servers.