What is it about? In-Stream Event Processing is a new approach for building near real time big data systems with rapidly growing user base and applications like clickstream analytics, preventive maintenance or fraud detection. Maturity of some open source projects enables building an enterprise grade In-Stream Processing service in-house. However the open source world comprises of many competing projects of different maturity, having different perspectives so the task to select effective and efficient projects is not straightforward. In the talk I’ll present a blueprint of an In-Stream Processing Service, enterprise grade reliable and scalable, cloud ready, build from 100% open source components.