The only requirement for the example web app that you use is that it returns something to be displayed in a user's web browser. One page/view with "Hello World" on it is perfectly adequate - this is just a placeholder. We don't want you to have to take the time to write a sample web app yourself.
Here is a list of "Hello World"-style example applications that we've found in various languages and frameworks. Feel free to use one of these, or find (or write, if you really want, though we wouldn't recommend it) one of your own. We haven't tried all of these, nor are they representative of the languages we use, so please keep that in mind.
- Django (Python) - Writing your first Django app, part 1 | Django documentation | Django or Chapter 2: Hello World app | Django For Beginners (code on GitHub)
- Express (Node.js) - Express "Hello World" example - expressjs.com
- Flask (Python) - Flask's QuickStart documentation includes a minimal 6-line Hello World implementation.
- Go - Go Web Examples has a minimal Hello World in Go example. There is also the golang.org Writing Web Applications and a Hello World tutorial with code on Soham Kamani's blog.
- Laravel (PHP) - niwasawa/php-laravel-hello-world: A sample code of PHP with Laravel or the slightly more complicated Basic Task List - Laravel - The PHP Framework For Web Artisans (source code at github.com/laravel/quickstart-basic: A sample task list application.)
- Meteor.js (Node.js) - official tutorials with React, Blaze and Angular as well as finished step-by-step repositories (React, Blaze and Angular). The Beginner's Guide to Meteor by Flavio Copes also has a minimal example.
- Rails (Ruby) - github.com/IBM-Cloud/ruby-rails-helloworld: A simple Ruby on Rails Hello World application or the slightly more involved Getting Started with Rails — Ruby on Rails Guides
- Serverless Framework has Example projects for various infrastructure providers including:
- AWS Lambda Hello World Examples in C#, F#, Go, Node.js, Python, and Ruby.
- Google Cloud Function Hello World Examples in Node.js and Python
- Azure Functions Hello World Example in Node.js
- Many others in github.com/serverless/examples: Serverless Examples – A collection of boilerplates and examples of serverless architectures built with the Serverless Framework on AWS Lambda, Microsoft Azure, Google Cloud Functions, and more.
- SpringBoot (Java) - 11. Developing Your First Spring Boot Application - docs.spring.io
- Symfony (PHP) - github.com/symfony/demo: Symfony Demo Application
- Yii (PHP) - yiisoft/yii2-app-basic: Yii 2.0 Basic Application Template
- Zappa (Python serverless toolkit) - Zappa/example at master · Miserlou/Zappa or a tutorial at Building a Simple API with Amazon Lambda and Zappa | Viget