Design an application performance monitoring system.

Focus on the key components that make up an effective application performance monitoring (APM) system. Discuss the types of metrics you would track, such as response times, error rates, and resource utilization. Consider how you would implement real-time monitoring and alerting mechanisms to detect performance issues as they arise. Address the importance of user experience in your design, including how you would visualize data for different stakeholders. Finally, think about scalability and how your system could adapt to varying loads and environments.