When doing a customer demo, I often need a simple app. Generally I am discussing the infrastructure – Elastic Load Balancer, API Gateway, etc – and the application is unimportant. I have found that phpinfo is a great sample application because it shows the headers received by the server. This allows me to see x-forwarded-for headers, etc. On Windows, ASP.NET Tracing provides similar results. Keep in mind that these utilities expose a lot of info about your environment so use them wisely.