Rails is a Ruby framework that employs the Model-View-Controller architecture for web application development, integrating databases like MySQL and PostgreSQL and web servers such as Apache and NGINX. This guide illustrates how to use Datadog for monitoring a Rails application running on Passenger, Apache, and MySQL by collecting metrics, request traces, and logs. The process involves installing the Datadog Agent, configuring log collection for different components, and setting up Rails application performance monitoring using the ddtrace gem. Datadog's APM provides insights into service-level performance by tracing requests across services, automatically generating dashboards for key metrics. Additionally, Datadog allows log collection from various sources, supports JSON-formatted logs through the Lograge gem, and enables custom dashboards and alerts for comprehensive monitoring. The guide also details enabling Datadog’s Apache and MySQL integrations for metrics and logs collection, facilitating efficient infrastructure monitoring and troubleshooting through Datadog's customizable tools.