Apache Eagle is a distributed real-time monitoring and alerting engine for Hadoop created by eBay to address limitations of existing tools in handling large volumes of metrics and logs from Hadoop clusters. It provides data activity monitoring, job performance monitoring, and unified monitoring. Eagle detects anomalies using machine learning algorithms and notifies users through alerts. It has been deployed across multiple eBay clusters with over 10,000 nodes and processes hundreds of thousands of events per day.