IAS installs into an application server and runs as a hosted application. IAS supports both WebLogic Server and Jetty Web server.
You typically install IAS into WebLogic Server in scenarios where your other Endeca products are also running in WebLogic Server and in production environments. For example, you might have IAS, Integrator ETL, Studio, and Endeca Server running as applications in WebLogic Server. Note however, IAS does not require many features provided by WebLogic, so this installation approach is primarily for ease of administration when hosting the entire Endeca stack.
You typically install IAS into Jetty in scenarios where you want a light-weight Web server to host IAS while you perform data development work in a development environment.