When it comes to web app development, Ruby on Rails stands out for its robust features that streamline the development process. One of the top features is the Convention over Configuration principle, which allows developers to focus on writing code rather than configuring files. This principle simplifies the setup and boosts productivity, enabling teams to deploy applications faster. Additionally, Ruby on Rails employs a powerful Active Record feature that simplifies database interactions. It provides an intuitive way to create and manage database records, making it easier to develop applications without needing extensive SQL knowledge.

Another essential feature is the Built-in Testing framework, which allows developers to execute test-driven development (TDD) practices seamlessly. This testing framework encourages writing tests for each piece of code, ensuring high-quality applications with fewer bugs. Furthermore, the framework supports RESTful architecture, making it simple to create applications that follow standard web protocols. Lastly, the extensive gem library expands Ruby on Rails capabilities, allowing developers to easily implement third-party solutions and functionalities, enhancing their web applications with minimal effort.

Scaling your Rails application effectively involves understanding its architecture and optimizing its performance. Start by analyzing the current state of your Rails application to identify bottlenecks. Common areas to examine include database queries, server response times, and background job processing. Utilize tools like New Relic or ScoutAPM to monitor performance metrics and gain insights into where slowdowns occur. After gathering data, consider refactoring your codebase by following best practices such as using the Rails asset pipeline to manage resources and implementing caching strategies with Redis or Memcached.

Once you have optimized your code, it’s essential to focus on your deployment strategy. Ensure your application can handle increased traffic by employing techniques like database sharding or load balancing. You might also want to deploy your application on a scalable platform like AWS or Heroku, which allows for horizontal scaling when necessary. This can be achieved using tools such as Docker for containerization, which simplifies the process of managing dependencies and optimizing performance. Lastly, always perform load testing before going live with your changes to ensure that your application can handle the load efficiently.

Building web applications with Rails can present several common challenges that developers must navigate. One of the most prevalent issues is managing dependencies effectively. With the frequent updates to Ruby and various gems, compatibility can become a significant headache. To tackle this, consider using tools like Bundler to manage gem versions and ensure consistent environments across development, testing, and production. Additionally, regularly updating your dependencies and utilizing tools such as Dependabot can help you stay on top of potential incompatibility issues.

Another challenge in Rails development is performance optimization. As your application scales, you may encounter slow database queries or increased response times. To overcome this, leverage Active Record features like eager loading to reduce the number of database queries. Furthermore, implementing caching strategies such as fragment caching or using tools like Redis can significantly improve your application’s performance. Monitoring your app's performance metrics through tools like New Relic can also help identify and address bottlenecks in real-time.