The document discusses building an IoT infrastructure on the edge with .NET that connects devices like Raspberry Pis and ESP32s to Azure. It describes setting up a network of Raspberry Pi devices running .NET Core and connecting sensors to collect data and send events to an Apache Kafka cluster. The events are then aggregated using Apache Spark on another Raspberry Pi and the results routed to the cloud. Issues encountered include Kafka's Java dependencies, Spark's complex processing model, and lack of documentation around integrating Pi, Kafka and Spark. While the technologies work individually, configuring and integrating them presented challenges at the edge.